1. health and fitness
2. disease

Antivirals, Herpes Simplex Virus (HSV)
Therapeutic Class Review (TCR)
February 23, 2012
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Page 1 of 17
February 2012
Antivirals, Herpes Simplex Virus (HSV) Review
FDA-APPROVED INDICATIONS
Drug
acyclovir (Zovirax )
Manufacturer
1
famciclovir (Famvir )
generic
2
generic
FDA-Approved Indications







valacyclovir (Valtrex )
3
generic




Treatment of herpes zoster (shingles)
Treatment of varicella (chickenpox) in patients > two years old
Treatment of genital herpes simplex (initial and recurrent episodes)
Treatment of herpes zoster (shingles)
Treatment and suppression of recurrent genital herpes in
immunocompetent adults
Treatment of recurrent episodes of orolabial or genital herpes
infections in HIV-infected patients
Treatment of recurrent herpes simplex labialis (cold sores) in
immunocompetent adults
Treatment of herpes zoster (shingles)
Treatment of genital herpes
Immunocompetent patients with initial or recurrent episode
Suppression in immunocompetent or HIV-infected patients
Reducing heterosexual transmission to susceptible partners
Treatment of herpes labialis (cold sores) in patients ≥12 years old)
Treatment of varicella (chickenpox) in immunocompetent patients two
to 18 years old
OVERVIEW
In 2010 The Centers for Disease Control and Prevention (CDC) estimated that there are 19 million new
sexually transmitted disease infections every year in the United States.,4. Herpes simplex virus type-2
(HSV-2) infections are the most common cause of genital ulceration in the United States with a
seroprevalence of approximately 16% or 17% nationwide HSV-2 seroprevalence is more common in
women and non-hispanic blacks.5 HSV is most often transmitted by people unaware they have
infection and/or are asymptomatic. HSV shedding can occur when the patient is asymptomatic. There
are two types of herpes simplex virus, HSV-1 and HSV-2. HSV-1 usually establishes latency in the
trigeminal ganglion and produces lesions on the lower lip or face. HSV-2 resides in the sacral ganglion
at the base of the spine and produces lesions and/or viral shedding in the genital area. It is possible to
have either virus affecting either region as well as other areas. HSV-2, by causing genital ulcerations,
has been found to increase the risk of acquiring human immunodeficiency virus (HIV). 6
HSV infections are chronic, life-long infections. Management of genital herpes includes counseling and
methods to reduce transmission such as use of condoms, avoidance of sexual activity during infection
recurrences, and suppressive antiviral therapy. Antivirals do not eradicate HSV. Antivirals partially
control the signs and symptoms of infection and are used for treatment of initial and recurrent herpes
episodes and as daily suppressive therapy to reduce the frequency of episodes.
The 2010 Centers for Disease Control and Prevention (CDC) Sexually Transmitted Diseases (STD)
recommendations for genital herpes either for initial or recurrent episodes indicate no preference for
any one of these three oral agents.7 Chronic suppressive therapy for patients with frequent
recurrences may include any one of the three oral agents according to the CDC STD guidelines. Oral
antiviral therapy is preferred over topical antiviral therapy. Topical treatment with antivirals offers
minimal clinical benefit, and its use is discouraged.
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February 2012
Antivirals, Herpes Simplex Virus (HSV) Review
Varicella-zoster virus (VZV) causes an acute, localized infection commonly known as chickenpox, and
then VZV lies dormant in the dorsal root ganglia for many years before potentially re-emerging to
cause herpes zoster, commonly known as shingles. Approximately one in three persons will develop
herpes zoster during their lifetime, resulting in an estimated one million episodes in the United States
annually. The risk of post-herpetic neuralgia in patients with herpes zoster is 10 to 18 percent.
Reactivation of VZV may be due to aging, stress, or immunosuppression. The virus spreads along nerve
tracts, causing pain or a burning sensation followed by a painful, blistering rash. The infection may
spontaneously disappear after two to three weeks and rarely recurs. Relief of pain may be all that is
required. In severe cases of shingles, nerve palsy, continued neuralgia, or blindness as a result of eye
lesions caused by VZV, may persist after the acute infection disappears. The goal of treatment of
herpes zoster is to reduce pain in immunocompetent patients and stop viral replication in
immunocompromised patients and those with ophthalmic herpes zoster.8 Antivirals reduce the
duration of viral shedding, new lesion formation, and healing of the rash. The effect of antivirals on the
development of postherpetic neuralgia are less clear; however, several meta-analyses and clinical trials
have demonstrated that antivirals significantly reduce the duration or incidence of prolonged
pain.9,10,11,12 Risk factors for postherpetic neuralgia include older age, female gender, presence of
prodromal symptoms, greater rash severity, and greater acute pain severity.13 The 2007 guidelines for
the management of herpes zoster support the use of any of the three agents for first line therapy. 14
The Advisory Committee on Immunization Practices (ACIP) recommends the use of a live attenuated
vaccine for persons 60 years and older for the prevention of herpes zoster. 15
PHARMACOLOGY
Drug
acyclovir (Zovirax)
Mechanism of Action
16


famciclovir
17
(Famvir)
valacyclovir
18
(Valtrex)



Acyclovir is an acyclic analogue of the natural nucleoside, guanosine. It is activated via
monophosphorylation by HSV-induced thymidine kinase. Selective affinity results in the
activation and concentration of acyclovir in virus-infected cells over normal cells. Two additional
phosphorylations result in acyclovir triphosphate, a substrate for and preferential inhibitor of
viral, rather than cellular, DNA polymerase. It binds to HSV DNA polymerase, is incorporated into
viral DNA, and thereby inhibits viral DNA replication.
Acyclovir has in vitro inhibitory activity against HSV-1, HSV-2, VZV, Epstein-Barr virus (EBV), and
cytomegalovirus (CMV).
Famciclovir is a pro-drug; it is the diacetyl 6-deoxy analog of the active antiviral compound,
penciclovir. Penciclovir is phosphorylated into a monophosphate form that is converted into
penciclovir triphosphate. Viral DNA synthesis and replication are inhibited by penciclovir.
Famciclovir has inhibitory activity against HSV-1, HSV-2, VZV, and EBV.
Valacyclovir is the L-valyl ester prodrug of acyclovir and is rapidly converted to acyclovir, which
has affinity for the viral enzyme thymidine kinase encoded by HSV and VZV. Therefore,
valacyclovir has similar viral inhibitory activity as acyclovir.
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February 2012
Antivirals, Herpes Simplex Virus (HSV) Review
PHARMACOKINETICS
Drug
acyclovir (Zovirax)
Bioavailability
(%)
Half-Life
(hr)
Metabolism
Excretion
(%)
10-20
2.5-3.3
At least one metabolite
Renal: 62-91
Fecal: minimal
77
2.3 for
penciclovir
One active – penciclovir;
three inactive
Renal:
Fecal:
73
27
55
2.5-3.3
Rapidly converted to
acyclovir
Renal:
Fecal:
46
47
19
famciclovir (Famvir)
20
valacyclovir (Valtrex)
21
CONTRAINDICATIONS/WARNINGS22,23,24
Acyclovir (Zovirax) and valacyclovir (Valtrex) are contraindicated in patients with hypersensitivity to
acyclovir. Famciclovir (Famvir) is contraindicated in patients with known hypersensitivity to the
product, its components or penciclovir cream (Denavir®).
Renal failure, in some cases resulting in death, has been observed with acyclovir and valacyclovir
therapy. Thrombocytopenic purpura/hemolytic uremic syndrome (TTP/HUS), which has resulted in
death, has occurred in immunocompromised patients receiving acyclovir or valacyclovir including
patients with advanced HIV disease, patients having undergone allogenic bone marrow transplant, and
renal transplant. Cases of acute renal failure have been reported in patients with underlying renal
disease who have received inappropriately high doses of famciclovir for their level of renal function.
Dosage reduction is recommended when administering famciclovir to patients with renal impairment.
Central nervous system adverse effects such as agitation, hallucinations, confusion, and
encephalopathy may occur in elderly patients (with or without reduced renal function) and in patients
with underlying renal disease who receive higher than recommended doses of valacyclovir for their
level of renal function. Use with caution in elderly patients and reduce dosage in patients with renal
impairment. Valacyclovir should be discontinued if CNS adverse effects occur.
Caution should also be exercised when administering acyclovir to patients receiving potentially
nephrotoxic agents since this may increase the risk of renal dysfunction and/or the risk of reversible
central nervous system symptoms such as those that have been reported in patients treated with
intravenous acyclovir. Adequate hydration should be maintained.
DRUG INTERACTIONS25,26,27
Coadministration of probenecid with intravenous acyclovir (Zovirax) has been shown to increase the
mean acyclovir half-life and the area under the concentration-time curve. Urinary excretion and renal
clearance were correspondingly reduced.
Concurrent use with probenecid or other drugs significantly eliminated by active renal tubular
secretion may result in increased plasma concentrations of penciclovir, the active metabolite of
famciclovir.
No clinically significant drug interactions have been observed with valacyclovir (Valtrex).
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Antivirals, Herpes Simplex Virus (HSV) Review
ADVERSE EFFECTS
Drug
Headache
Nausea
Dizziness
Abd. Pain
 AST
Diarrhea
reported
(2.2)
4.8
(2.4)
reported
nr
reported
2.4
(2.7)
13.5-22.7
(5.4-17.8)
2.5-12.5
(3.6-11.6)
nr
0-1.1
(1.2-3.4)
2.3
(1.2)
4.9-7.7
(1.2-4.8)
11-38
(8-14)
4-15
(5-8)
2-4
(1-2)
3-11
(2-6)
1-4.1
(0-3)
nr
28
acyclovir (Zovirax)
400 mg twice daily
n=586 continuous treatment
(n=589 intermittent treatment
of occurrences)
29
famciclovir (Famvir)
125 mg daily to 1 gm twice daily
30
valacyclovir (Valtrex)
500 mg twice daily to
1 gm three times daily
Adverse effects are reported as a percentage. Adverse effects data are obtained from prescribing information and are not
meant to be comparative or all inclusive. Incidences for the placebo group are indicated in parentheses. nr = not reported.
AST = aspartate aminotransferase
In clinical studies for the treatment of herpes labialis in adolescents with valacyclovir, the adverse
effects most commonly reported were headache (17 percent) and nausea (eight percent). In pediatric
patients (ages one month to 12 years of age), adverse effects reported in pharmacokinetic and safety
studies of valacyclovir included diarrhea (five percent), pyrexia (four percent), dehydration (two
percent), herpes simplex (two percent), and rhinorrhea (two percent).
SPECIAL POPULATIONS31,32,33
Pediatrics
Herpes infections
Intravenous acyclovir (Zovirax) has been shown to be safe in pediatric patients, but safety and
effectiveness of oral formulations of acyclovir in children less than two years of age have not been
established.34 Safety and efficacy in children less than 18 years of age have not been established for
famciclovir (Famvir).
Valacyclovir (Valtrex) is approved for the treatment of herpes labialis episodes in children 12 years of
age and older.
Varicella infections
Acyclovir is approved for treatment of varicella in children two years of age and older. The use of
acyclovir for the treatment of varicella in children has decreased since the arrival of the varicella
vaccine for the prevention of varicella infections in children.
Valacyclovir is approved for the treatment of chickenpox in children ages two to 18 years of age.
Valacyclovir oral suspension (25 mg/mL or 50 mg/mL) can be prepared from the 500 mg caplets;
acyclovir is available as an oral suspension.
Acyclovir has been shown to be effective in the treatment of chickenpox in at least two double-blind
placebo-controlled studies in normal children ages two to 16 years that were performed in the early
1990’s prior to the availability of the varicella vaccine for children.35,36 Treatment in both studies began
within 24 hours of rash onset and was given as acyclovir 20 mg/kg four times daily for five to seven
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Antivirals, Herpes Simplex Virus (HSV) Review
days. Children ages 12 to 16 years received 10 mg/kg four times daily orally for five to seven days.
Beneficial effects of acyclovir included earlier defervescence, fewer varicella lesions, absence of new
lesions after three days of acyclovir, and accelerated crusting and healed stages. No differences in
disease complications were noted in either study. Acyclovir was well tolerated in the children with no
serious adverse effects reported.
Pregnancy
Acyclovir, famciclovir, and valacyclovir are Pregnancy Category B.
Prevention of neonatal exposure to herpes requires the avoidance of contracting genital HSV during
the third trimester and avoidance of exposure of the infant to active herpetic lesions during delivery.37
Safety data for agents in this category are not robust; the majority of data are with acyclovir.
HIV-positive patients
Patients with HIV may have severe and prolonged episodes of HSV lesions. 38 In general, HSV shedding
is more common in patients with HIV. The CDC recommends any one of the three agents for daily
suppressive therapy in patients infected with HIV. Resistance of HSV to all of these drugs is higher in
immunocompromised patients (six to seven percent) than in immunocompetent patients (<0.5
percent).39,40,41
Renal Impairment
All products in this category require dose and/or interval adjustments for renal impairment.
Elderly
Elderly patients are more likely to have reduced renal function and require dose reduction. Elderly
patients are also more likely to have increased renal or CNS adverse events with valacyclovir and
acyclovir. In clinical studies accessing the efficacy of famciclovir in treating herpes zoster; there were
no differences in overall adverse effects between younger and older patients. Thus, there are no
suggested dosage adjustments in geriatric patients treated with famciclovir. Yet, caution should be
taken when administering all HSV agents to elderly patients due to decrease renal function associated
with age.
African American patients
A double blind placebo controlled study with 299 patients showed similar efficacy and tolerability of
one day treatment with famciclovir 1,000 mg twice daily compared to placebo in immunocompetent
Black adults with recurrent genital herpes. Further understanding of the efficacy of antiherpes therapy
in Black patients with recurrent genital herpes may be warranted.42
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Antivirals, Herpes Simplex Virus (HSV) Review
DOSAGES
FDA-Approved Dosages
Drug/
Dosage Forms
acyclovir (Zovirax)
200 mg capsule;
400, 800 mg
tablets;
200 mg/5 mL
suspension
Initial
genital
herpes
Recurrent
genital herpes
Chronic
suppressive
genital herpes
Herpes
zoster
800 mg
200 mg
200 mg
400 mg twice daily five times
five times
five times per
for up to 12
per day for
per day for
day for five days
months
seven to ten
10 days
days
Herpes labialis
(cold sores)
--
Varicella
2 years and
older:
Less than
40 kg:
20 mg/kg per
dose orally 4
times daily for
five days
40 kg and up: 800
mg four times a
day for five days
famciclovir (Famvir)
125, 250, 500 mg
tablets
1 gm twice daily
for one day
--
valacyclovir
(Valtrex)
500, 1,000 mg
caplets
1,500 mg as a
single dose
250 mg twice daily
For HIV+
for up to 12
patients, 500 mg
months
twice daily for
seven days for
genital herpes
500 mg three
For HIV+
times daily
patients,
500 mg
for seven
twice
daily
for
days
seven days for
orolabial herpes
500 mg – 1 gm
daily
1 gm twice
daily for
ten days
500 mg twice
daily for three
days
For HIV-infected
patients,
500 mg twice daily
For reduction of
heterosexual
transmission: 500
mg daily
1 gm three
times daily
for seven
days
--
Ages 2 to <18
years:
≥ 12 years:
20 mg/kg three
2 gm every
times daily for
twelve hours for
five days; not to
one day
exceed 1 gm
three times daily
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Antivirals, Herpes Simplex Virus (HSV) Review
Dosages (continued)
CDC Recommended Dosages for Genital HSV infections43
Drug
acyclovir (Zovirax)
famciclovir (Famvir)
Initial genital herpes
200 mg
five times per day for
7 to 10 days
OR
400 mg three times daily
for 7 to 10 days
250 mg three times daily
for 7 to 10 days
valacyclovir (Valtrex) 1 gm twice daily for
7 to 10 days
Recurrent genital herpes
Chronic suppressive genital
herpes
400 mg three times daily for
five days
OR
800 mg twice daily for five days
OR
800 mg three times daily for
two days
400 mg twice daily
For HIV-positive patients:
400 mg three times daily for
5 to 10 days
For HIV-positive patients:
400 to 800 mg twice to three times
daily
125 mg twice daily for five days
OR
1 gm twice daily for one day
OR
500 mg for 1 dose, then 250 mg
twice daily for two days
250 mg twice daily
For HIV-positive patients:
500 mg twice daily for 5 to 10
days
For HIV+ patients:
500 mg twice daily
500 mg twice daily for three days
OR
1 gm once daily for five days
500 mg* – 1 gm daily
For HIV-positive patients:
For HIV-positive patients:
1 gm twice daily for five to 10 days 500 mg twice daily
* Valacyclovir 500 mg daily for suppressive therapy may be less effective than other regimens in patients with high
frequency recurrences (>10 episodes per year).
CLINICAL TRIALS
Search Strategy
Studies were identified through searches performed on PubMed and review of information sent by
manufacturers. Search strategy included the FDA-approved use of all drugs in this class. Randomized,
comparative, controlled trials performed in the United States comparing oral agents within this class in
an outpatient setting for the approved indications are considered the most relevant in this category.
Studies included for analysis in the review were published in English, performed with human
participants, and randomly allocated participants to comparison groups. In addition, studies must
contain clearly stated, predetermined outcome measure(s) of known or probable clinical importance,
use data analysis techniques consistent with the study question, and include follow-up (endpoint
assessment) of at least 80 percent of participants entering the investigation. Despite some inherent
bias found in all studies, including those sponsored and/or funded by pharmaceutical manufacturers,
the studies in this therapeutic class review were determined to have results or conclusions that do not
suggest systematic error in their experimental study design. While the potential influence of
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Antivirals, Herpes Simplex Virus (HSV) Review
manufacturer sponsorship/funding must be considered, the studies in this review have also been
evaluated for validity and importance.
Herpes Zoster - uncomplicated
acyclovir (Zovirax) versus famciclovir (Famvir)
In a double-blind, parallel-group study, 55 immunocompetent adults with acute uncomplicated herpes
zoster were randomized to treatment with famciclovir 250 mg three times daily or acyclovir 800 mg
five times daily.44 This study compared the clinical efficacy of acyclovir and famciclovir in the treatment
of acute uncomplicated herpes zoster. Treatment was initiated within 72 hours of onset of the zoster
rash and was continued for seven days. Famciclovir was as effective as acyclovir for healing the
cutaneous lesion, as indicated by the time to full crusting (11 days with famciclovir, 10 days with
acyclovir; p=0.761) and loss of acute phase pain (famciclovir 20 days, acyclovir 27 days; p=0.683). Both
groups experienced loss of vesicles on day six. Loss of ulcers occurred in one day in both groups. Loss
of crusts were similar between the two groups (acyclovir 27 days; famciclovir 20 days; p=0.558).
Famciclovir was well tolerated and had a more favorable adverse event profile compared to acyclovir.
Constipation, hematuria, and glycosuria were the most commonly reported adverse events. The dose
of famciclovir used in this study is 50 percent lower than the approved dosage for this indication.
Another double-blind study compared the clinical efficacy of acyclovir 800 mg five times daily and
famciclovir 750 mg once daily, 500 mg twice daily, or 250 mg three times daily in the treatment of
acute uncomplicated herpes zoster in immunocompetent adults.45 Patients (n=559) presented within
72 hours after rash onset and were randomized to famciclovir 750 mg daily, 500 mg twice daily, or 250
mg three times daily or acyclovir 800 mg five times daily. All patients were given treatment for seven
days. Complete healing was assessed at four weeks or whenever completed healing occurred. Healing
was defined as time to full crusting of lesions, loss of vesicles, cessation of new lesion formation, and a
50 percent reduction in affected skin. Healing and loss of acute pain were similar among the four
groups. The development of postherpetic neuralgia was not assessed in this study. Headache was the
most commonly reported adverse effect. Five discontinuations were reported with both famciclovir
and acyclovir. The doses of famciclovir used in this study are one-third to one-half lower than the dose
recommended for this indication.
acyclovir (Zovirax) versus valacyclovir (Valtrex)
A randomized, double-blind, multicenter trial evaluated the safety and efficacy of acyclovir and
valacyclovir in the treatment of herpes zoster in 1,141 immunocompetent adults.46 Patients presented
within 72 hours of onset of rash. Patients were randomized to one of three groups: valacyclovir 1 gm
three times daily for seven or 14 days or acyclovir 800 mg five times daily for seven days. The primary
outcome parameters were the succession of pain, time to cessation of new lesion formation and/or
increase in lesion area, and time to greater than 50 percent crusting or healed rash. Valacyclovir
treatment for seven or 14 days significantly accelerated the resolution of pain (p=0.001 and p=0.03,
respectively) compared with acyclovir treatment. Median cessation of pain was 38 and 44 days,
respectively, with valacyclovir seven- or 14-day treatments compared to 51 days with acyclovir. No
significant differences in time to cessation of new lesions and or increase in lesion area were reported
among the groups [valacyclovir seven-day versus acyclovir [HR=1.03 (95% CI, 0.89-1.20)]; valacyclovir
14-day versus acyclovir [HR=0.99 (95% CI, 0.85-1.14)]; valacyclovir seven- versus 14-day [HR=1.05 (95%
CI, 0.91-1.21)]. No significant differences in the time to greater than 50 percent crusting or healing
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Antivirals, Herpes Simplex Virus (HSV) Review
lesions were reported among the groups {valacyclovir seven-day versus acyclovir [HR=1.00 (95% CI,
0.87-1.16)]; valacyclovir 14-day versus acyclovir [HR=1.02 (95% CI, 0.88-1.18)]; valacyclovir sevenversus 14-day [HR=0.98 (95% CI, 0.85-1.14)]}. Valacyclovir 14-day group had a shorter duration of
abnormal sensations compared to acyclovir [HR=1.27 (95% CI, 1.07-1.52)]. All other groups were
similar. No significant differences in pain intensity, quality of life or unpleasantness were reported
among the groups. Valacyclovir seven- and 14-day groups had a similar percentage of patients
reporting pain after six months (19.9 and 18.6 percent, respectively) that was significantly lower than
the percent reporting the same in the acyclovir group (25.7 percent; valacyclovir versus acyclovir,
p=0.02). No differences in adverse drug events were observed among the groups.
famciclovir (Famvir) versus valacyclovir (Valtrex)
A study compared the clinical efficacy of valacyclovir 1 gm three times per day to famciclovir 500 mg
three times a day for seven days in the treatment of acute uncomplicated herpes zoster. 47 A total of
597 outpatients, aged 50 years and older, who had herpes zoster were enrolled in a double-blind,
randomized trial. The primary outcome was complete cessation of zoster-related pain. The occurrence
of postherpetic neuralgia was also assessed. Secondary endpoints included time to cessation of zosterassociated abnormal sensations, pain intensity, rash healing, and lesion dissemination. No difference in
resolution of zoster related pain were seen in this comparison of valacyclovir (42 days) and famciclovir
[49 days; HR=1.02 (95% CI, 0.84-1.23)]. Postherpetic neuralgia was similar in both groups [HR=1.01
(95% CI, 0.84-1.23)]. No differences were reported with any of the secondary endpoints including time
to cessation of zoster-associated abnormal sensations, pain intensity, rash healing (p=0.26), and lesion
dissemination. Headache and nausea were the most common events reported for each agent.
Herpes zoster – immunocompromised patients
acyclovir (Zovirax) versus famciclovir (Famvir)
In a randomized, double-blind, multicenter study, 148 patients (ages 12 years and older) with clinical
evidence of localized herpes zoster received either oral famciclovir 500 mg three times daily or
acyclovir 800 mg five times daily for ten days.48 The efficacy and safety of famciclovir were evaluated
for the treatment of herpes zoster in patients who were immunocompromised following bone marrow
(BMT) or solid organ transplantation or oncology treatment. An equivalent percentage of patients in
the famciclovir and acyclovir groups, 77 and 73 percent, respectively, reported new lesion formation
while on therapy. The median time to cessation of new lesions was three days with acyclovir and four
days with famciclovir. The median time to full crusting was eight days for famciclovir and nine days for
acyclovir [HR=1.26 (95% CI, 0.88-1.82)]. The median time to complete healing was 20 days with
famciclovir and 21 days with acyclovir [HR=0.98 (95% CI, 0.67-1.42). The median time to loss of acute
pain was 14 and 17 days for famciclovir and acyclovir, respectively [HR=0.71 (95% CI, 0.71-1.75)]. In
summary, there were no significant differences between the groups in the median time to cessation of
new lesion formation, full crusting, complete healing of lesions, or loss of acute phase pain. Treatment
with famciclovir was well tolerated with a safety profile comparable to that of acyclovir.
Herpes Zoster - ophthalmic
acyclovir (Zovirax) versus famciclovir (Famvir)
Famciclovir and acyclovir were compared in a randomized, double-blind trial with 454 patients with
ophthalmic herpes zoster involving the trigeminal nerve.49 Therapy was famciclovir 500 mg three times
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Antivirals, Herpes Simplex Virus (HSV) Review
daily or acyclovir 800 mg five times daily for seven days. Ocular manifestations of ophthalmic zoster
were similar in the two groups (famciclovir, 58 percent versus acyclovir, 58.2 percent). There was no
difference in visual acuity loss either. Both therapies were well tolerated.
acyclovir (Zovirax) versus valacyclovir (Valtrex)
A multicenter, double-blind study enrolled 110 immunocompetent patients with ophthalmic herpes
zoster diagnosed within 72 hours of skin eruption.50 Patients were randomized to treatment with
valacyclovir 1 gm three times daily or acyclovir 800 mg five times daily, each with matching placebo
control. Ocular complications of ophthalmic herpes zoster were similar in the valacyclovir and acyclovir
treatment groups with the main complications being conjunctivitis (54 and 52 percent), superficial
keratitis, stromal keratitis (both 13 percent), and uveitis (13 and 17 percent). Pain duration and
severity and outcome of skin lesions were similar between groups. Pain was reported after one month
in 25 percent of the valacyclovir group and 31 percent in the acyclovir group. Three percent of each
group reported pain at week 24. Both valacyclovir and acyclovir produced similar outcome for skin
lesions. Total healing (100 percent) was reported in 83 and 87 percent of the valacyclovir and acyclovir
groups, respectively, at day 14. The most frequent adverse events were vomiting and edema of the
eyelids or face, which occurred in three to five percent of patients.
Genital Herpes Simplex – initial episode
acyclovir (Zovirax) versus valacyclovir (Valtrex)
A multicenter, randomized, double-blind clinical trial compared ten-day regimens of valacyclovir 1 gm
twice daily and acyclovir 200 mg five times daily in the treatment of 643 healthy adults with firstepisode genital herpes.51 Patients were enrolled if symptoms had presented in less than 72 hours prior
to enrollment. Patients received the randomized therapy plus a matching placebo. Patients (n=24) who
had antibodies to HSV-1 and HSV-2 were excluded from the analysis since this represented a recurrent
infection. Time to healing of all lesions and the duration of viral shedding were the primary outcome
parameters. Valacyclovir and acyclovir did not differ significantly in efficacy with respect to duration of
viral shedding (three days in both groups), portion of patients forming new lesions, duration of pain,
maximum number of lesions, and time to loss of all symptoms. Adverse experiences were generally
infrequent and mild and were comparable in the two treatment groups.
Genital Herpes Simplex - recurrent
acyclovir (Zovirax) versus famciclovir (Famvir)
Two hundred and four patients with recurrent genital herpes were randomized in a double-blind,
double-placebo, parallel-design study to famciclovir 125 mg twice daily or acyclovir 200 mg five times
daily.52 The mean time to complete healing of lesions was 5.1 days for famciclovir and 5.4 days for
acyclovir (p=NS). There were no differences detected in the proportion of patients having complete
healing at the different days of evaluation as well as in the duration until the complete resolution of all
the symptoms. The frequency, nature, and severity of adverse events did not differ between the two
treatment groups.
acyclovir (Zovirax) versus valacyclovir (Valtrex)
In a double-blind study, 739 patients with a history of recurrent genital HSV infection were randomized
to receive either oral valacyclovir 500 mg twice daily or acyclovir 200 mg five times daily for five days
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for treatment of their next recurrent episode.53 Patients self-initiated therapy at the first signs and/or
symptoms of the HSV recurrence, then were assessed in clinic on five occasions over seven days, then
twice weekly thereafter until lesions had healed. The time to healing of all lesions and the duration of
all signs and symptoms were the primary endpoints. Duration of episode which was the time from
treatment initiation to complete resolution of all signs and symptoms was similar between valacyclovir
(4.7 days) and acyclovir [4.6 days (HR=0.93; 95% CI, 0.79-1.08, p=0.34)]. Lesion healing time was similar
between valacyclovir (4.4 days) and acyclovir [4.5 days (HR=0.96; 95% CI, 0.80-1.14)]. Percentages of
patients in whom all HSV cultures were negative were similar in the valacyclovir and acyclovir groups at
59 and 54 percent, respectively. There was no difference in the ability of each drug to prevent the
development of vesicular/ulcerative lesions (HR=1.08, 95% CI, 0.82-1.42). Duration and severity of pain
were similar between the two groups (HR=0.93; 95% CI, 0.78-1.06). The safety profiles of valacyclovir
and acyclovir were comparable with adverse experiences being infrequent and generally mild. In
patient-initiated therapy, acyclovir 200 mg five times daily and valacyclovir 500 mg twice daily provide
similar time to healing all lesions and reduce the development of new lesions in recurrent genital HSV
infections.
In a multicenter, double-blind study, 1,200 people with recurrent genital HSV infections were
randomized to self-initiated oral therapy with valacyclovir 1 gm twice daily, acyclovir 200 mg five times
daily, or placebo for five days.54 The primary endpoints include the length of the episode and time to
lesion healing. Secondary endpoints include duration and severity pain and discomfort, viral shedding,
and proportion of aborted episodes. Valacyclovir [median duration until herpetic resolution 4.8 days,
HR=1.66 (95% CI, 1.33-2.01)] and acyclovir [4.8 days, HR=1.71 (95% CI, 1.41-2.06)] significantly reduced
the length of time of episode compared to placebo (5.9 days). Median healing times were significantly
earlier with valacyclovir [4.8 days, HR=1.88 (95% CI, 1.53 -2.32)] and acyclovir [4.8 days, HR=1.90 (95%
CI, 1.55-2.34)] compared to placebo (6.0 days). Pain duration was shorter in both active treatment
groups (both p<0.05), and viral shedding stopped earlier in patients on active treatment (both
p<0.001). Both active treatments reduced the severity of pain and discomfort compared to placebo on
day three (valacyclovir, p<0.001; acyclovir, p=0.001). Aborted episodes occurred more frequently with
valacyclovir (25.9 percent) and acyclovir (24.8 percent) than placebo (19.8 percent), although this did
not achieve statistical significance. The safety profiles of valacyclovir and acyclovir were comparable.
Valacyclovir and acyclovir reduce the length of a genital HSV episode and reduced the time to healing
compared to placebo. The dose of valacyclovir studied in this trial is twice the dosage recommended by
the CDC for this patient population.55
A study examined the dose-response relationship of valacyclovir given once daily for the suppression of
genital HSV infections in 1,479 immunocompetent patients with frequently recurring infections over 52
weeks.56 Twice-daily acyclovir and valacyclovir were also evaluated. In the randomized, double-blind
study, patients were randomized to valacyclovir 250, 500, or 1,000 mg once daily or 250 mg twice
daily, acyclovir 400 mg twice daily, or placebo for one year. All patients had a history of at least six
recurrences of genital herpes per year. Suppressive therapy was discontinued for at least three months
prior to enrollment. Episodic therapy with valacyclovir was given for five days for recurrences. The
primary endpoint was the time to first recurrence of genital HSV infection which was defined as
number of days since randomization until first onset of lesions. No significant difference between
active treatments for suppression HSV recurrences was demonstrated (all tested comparisons, p=NS);
all were significantly more effective than placebo at suppressing HSV recurrences (all comparisons
versus placebo; p<0.01). All valacyclovir treatment groups had longer time to first recurrence
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Antivirals, Herpes Simplex Virus (HSV) Review
compared to placebo. Acyclovir was not tested versus placebo but numerically looked to favor
acyclovir. The percentage of patients without recurrences were reported as follows: 48 percent of
valacyclovir 1 gm daily group, 40 percent of valacyclovir 500 mg daily group, 50 percent of valacyclovir
250 mg twice daily group, 22 percent of valacyclovir 250 mg daily group, 49 percent acyclovir group,
and five percent of the placebo group. Patients with >10 recurrences had a lower rate of response to
suppression overall. These patients are best treated with valacyclovir 1 gm daily, valacyclovir 250 mg
twice daily, or acyclovir 400 mg twice daily. Patients with <10 recurrences per year had a similar
response rate with valacyclovir 500 mg or 1 gm once daily or 250 mg twice daily or acyclovir 400 mg
twice daily. Adverse events were generally mild, infrequent, and similar in nature to placebo. The most
common adverse event reported in all groups was headache.
In a double-blind, three-period crossover trial, the efficacy in suppression of shedding of genital HSV in
69 immunocompetent patients was compared.57 Patients received valacyclovir 500 mg twice daily,
acyclovir 400 mg twice daily, or placebo for seven-week time periods in random order. Daily genital
mucosal swabs were collected from the patients. HSV was detected at least once in 90 percent of
patients by culture and 98 percent by DNA polymerase chain reaction (PCR). Genital HSV shedding
detected by culture was detected in 86 percent while on placebo, 12 percent while on valacyclovir and
24 percent while on acyclovir (both p<0.01). By PCR detection, HSV shedding was detected in 93, 65,
and 76 percent while on placebo, valacyclovir, and acyclovir, respectively (valacyclovir versus placebo,
p<0.001; acyclovir versus placebo, p=0.01). Antiviral therapy significantly reduced the HSV shedding
compared to placebo by both culture and PCR detection methods with no significant differences in
frequency or quantity of HSV shedding between the two antivirals. The geometric mean number of
HSV DNA detected PCR copies/mL decreased from 105.2 for placebo to 103.9 and 103.6 with valacyclovir
and acyclovir, respectively (both p<0.001 versus placebo). The levels of valacyclovir and acyclovir
suppression of HSV DNA were similar. Valacyclovir was associated with a significant decrease in the
frequency of total HSV shedding by both viral culture [RR=0.03 (95% CI, 0.01–0.07); p<0.001] and PCR
[RR=0.18 (95% CI, 0.12–0.26); p<0.001] compared to placebo. A similar decrease in the frequency of
total HSV shedding was observed with acyclovir compared with placebo [RR=0.05 (95% CI, 0.03–0.10)
for culture and RR=0.20 (95% CI, 0.15– 0.28) for PCR; p<0.001 for both]. Days with genital lesions were
reported in 2.8 percent for valacyclovir (p<0.001), 3.1 percent with acyclovir (p<0.001), and 22.1
percent with placebo.
famciclovir (Famvir) versus valacyclovir (Valtrex)
In a multicenter, multinational, double-blind, parallel-group study, 1,179 adults with a history of
recurrent genital herpes were randomized to receive either single-day famciclovir 1 gm (administered
twice daily) versus three-day valacyclovir 500 mg (administered twice daily).58 Patients initiated
treatment within six hours after a recurrence. Single-day famciclovir therapy was non-inferior to threeday valacyclovir therapy in reducing time to healing of all genital herpes lesions (median time to
healing, 4.25 days versus 4.08 days, respectively). There was no significant difference in time to
resolution of symptoms associated with recurrence. The overall incidence of adverse events was
similar (23.2 percent for the famciclovir group versus 22.3 percent for the valacyclovir group).
Additionally, the median time to next recurrence from treatment initiation was 33.5 days for
famciclovir and 38.0 days for valacyclovir.59 No drug resistance to penciclovir, the active metabolite of
famciclovir, was observed at baseline nor did any develop by the time of the next recurrence. The
study had no placebo arm, typing of viral isolates was not performed, and viral resistance testing was
restricted to penciclovir only.
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Antivirals, Herpes Simplex Virus (HSV) Review
famciclovir (Famvir) versus valacyclovir (Valtrex)
Two randomized, double-blind, placebo-controlled studies comparing daily famciclovir 250 mg bid with
valacyclovir 500 mg daily were performed. Study 1 randomized 320 participants and compared the
clinical effect of the drugs given for 16 weeks, and study 2 enrolled 70 HSV-2 seropositive subjects and
compared the virologic effect of the drugs given for 10 weeks.60 In study 1, the time to first recurrence
was similar in famciclovir and valacyclovir recipients, hazard ratio (HR) 1.17 (95% CI, 0.78-1.76), but
time to first virologically confirmed recurrence was shorter among famciclovir recipients, HR = 2.15
(95% CI, 1.00-4.60). In study 2, HSV was detected on 3.2 percent of days among famciclovir recipients
and 1.3percent of days among valacyclovir recipients relative risk 2.33 (95% CI, 1.18-4.89). Valacyclovir
appear to be somewhat better than famciclovir for suppression of genital herpes and associated
shedding.
Genital Herpes Simplex – reduced transmission
valacyclovir (Valtrex) versus placebo
A randomized, double-blind study evaluated the effectiveness of valacyclovir in reducing the risk of
transmission of genital herpes in heterosexual, monogamous discordant couples (n=1,484 couples). 61
The patients with HSV-2 were randomized to valacyclovir 500 mg once daily or placebo for eight
months. Of the participating couples, 78.1 percent completed the study. Over 70 percent of the source
partners reported taking at least 95 percent of the prescribed doses. Immunocompetent, heterosexual,
monogamous couples with one clinically infected with HSV-2 and the other susceptible to HSV-2 were
eligible for participation. The patient with recurrent genital herpes must have had fewer than 10
episodes per year, over 18 years of age, and use of daily antiviral therapy outside the study protocol
was not permitted. The inclusion criteria for the susceptible partner were an age of 18 years or older
and HSV-2 seronegativity. Both partners were required to be immunocompetent and in good health,
and the couple was required to use effective contraception. Acquisition of HSV-2 infection was defined
as the isolation of HSV-2 in culture, the detection of HSV-2 DNA, or HSV-2 seroconversion in the
susceptible partner during the course of the trial. Clinically symptomatic genital herpes infection in the
susceptible partner was a primary outcome of the study. A total of 41 new HSV-2 and four HSV-1
infections were acquired during the course of the study in the susceptible partners. Of these 45 new
infections, 14 were from sexual partners receiving valacyclovir and 31 were from partners receiving
placebo. Of the 20 symptomatic acquisitions of HSV-2, 16 occurred among the 741 partners of placebo
recipients (2.2 percent), as compared with four among the 743 partners of valacyclovir recipients (0.5
percent) (relative risk, 0.25; 95% CI, 0.08 to 0.74; p=0.01). HSV-2 had been acquired by 27 of the
susceptible partners of placebo recipients (3.6 percent) as compared with 14 of the susceptible
partners of valacyclovir recipients (1.9 percent) (hazard ratio, 0.52; 95% CI, 0.27 to 0.99; p=0.04). HSV-2
shedding occurred on 3.3 percent and 0.9 percent of the days among the valacyclovir-treated women
and men, respectively, as compared with 11.4 percent and 9.2 percent of the days among placebotreated women and men. Adverse effects were similar between the valacyclovir- and placebo-treated
patients. Valacyclovir 500 mg daily reduces the transmission of genital herpes in immunocompetent,
heterosexual, monogamous couples with one clinically infected with HSV-2 and the other susceptible
to HSV-2.
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Antivirals, Herpes Simplex Virus (HSV) Review
Herpes Labialis
There are no direct comparative trials with the oral antivirals for the treatment or prevention of herpes
labialis. All agents in this category have shown to prevent and treat oral HSV lesions in placebocontrolled studies.
The early trials with acyclovir from the 1980’s were generally small populations and open-label.62,63 A
number of other double-blind trials with acyclovir for oral herpes have been completed.64,65
Famciclovir has also been shown to be effective and safe in the prevention and treatment of oral HSV
infections and in the HIV-positive population.66,67,68,69 Valacyclovir has been studied in a variety of
dosage regimens for the treatment of recurring oral HSV infections including a simple two dose
regimen.70,71
META-ANALYSIS
Acyclovir has been shown to reduce fever earlier in acute varicella infection in otherwise healthy
children and adolescents according to a systematic review that included data through June 2005. 72
Studies were randomized controlled studies in children through age 18 years. Three studies were
included. Acyclovir reduced the number of days with fever (-1.1 days, 95% CI, -1.3 to -0.9) and reduced
the maximum number of lesions (-76 lesions, 95% CI, -145 to -8). Complications with chickenpox and
adverse effects were clinically important differences between acyclovir and placebo.
A meta-analysis compared the clinical efficacies of the different oral antiviral drugs prescribed
prophylactically to suppress recurrent genital herpes.73 A total of 14 randomized clinical trials were
selected, including a total of 6,158 patients. The global relative risk of developing at least one
recurrence during the study was reduced by 47 percent (95% CI, 45-49 percent) in antiviral drug groups
compared with the placebo. The best evaluated regimens, with comparable efficacies, were acyclovir
400 mg twice daily, valacyclovir 250 mg twice daily, famciclovir 250 mg twice daily, and valacyclovir
500 mg once daily. The analysis confirmed high clinical efficacy of all agents for the prevention of
recurrent genital herpes.
SUMMARY
The oral agents which are approved for herpes infections include acyclovir (Zovirax), famciclovir
(Famvir), and valacyclovir (Valtrex). Based on available data, all of the agents have similar efficacy and
adverse effects.
The 2010 CDC STD recommendations for genital herpes indicate no preference for any one of these
three agents over another for the treatment of initial or recurrent episodes of genital HSV infection.
Chronic suppressive therapy for patients with frequent recurrences may include any one of the three
agents; however, famciclovir may be slightly less effective for suppression of viral shedding in genital
herpes.
All three agents have similar efficacy for the treatment of herpes zoster, and recent guidelines support
the use of any of the three agents for first line therapy.
Both acyclovir and valacyclovir are approved for the treatment of varicella (chickenpox).
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Antivirals, Herpes Simplex Virus (HSV) Review
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59 Bodsworth N, Fife K, Koltun W, et al. Single-day famciclovir for the treatment of genital herpes: follow-up results of time to next recurrence and
assessment of antiviral resistance. Curr Med Res Opin. 2009; 25(2):483-7.
60 Wald A, Selke S, Warren T, Aoki FY, et al. Comparative efficacy of famciclovir and valacyclovir for suppression of recurrent genital herpes and viral
shedding. Sex Transm Dis. 2006; 33(9):529-33.
61 Corey L, Wald A, Patel R, et al for the Valacyclovir HSV Transmission Study Group. Once-daily valacyclovir to reduce the risk of transmission of genital
herpes. N Engl J Med. 2004; 350(1):11-20.
62 Spruance SL, Hamill ML, Hoge WS, et al. Acyclovir prevents reactivation of herpes simplex labialis in skiers. JAMA. 1988; 260(11):1597-1599.
63 Raborn GW, McGaw WT, Grace M, et al. Oral acyclovir and herpes labialis: a randomized, double-blind, placebo-controlled study. J Am Dent Assoc.
1987; 115(1):38-42.
64 Rooney JF, Straus SE, Mannix ML, et al. Oral acyclovir to suppress frequently recurrent herpes labialis. A double-blind, placebo-controlled trial. Ann
Intern Med. 1993; 118(4):268-272.
65 Spruance SL, Stewart JC, Rowe NH, et al. Treatment of recurrent herpes simplex labialis with oral acyclovir. J Infect Dis. 1990; 161(2):185-190.
66 Spruance SL, Bodsworth N, Resnick H, et al. Single-dose, patient-initiated famciclovir: a randomized, double-blind, placebo-controlled trial for episodic
treatment of herpes labialis. J Am Acad Dermatol. 2006; 55(1):47-53.
67 Romanowski B, Aoki FY, Martel AY, et al. Efficacy and safety of famciclovir for treating mucocutaneous herpes simplex infection in HIV-infected
individuals. Collaborative Famciclovir HIV Study Group. AIDS. 2000; 14(9):1211-1217.
68 Spruance SL, Rowe NH, Raborn GW, et al. Peroral famciclovir in the treatment of experimental ultraviolet radiation-induced herpes simplex labialis: A
double-blind, dose-ranging, placebo-controlled, multicenter trial. J Infect Dis. 1999; 179(2):303-310.
69 Schacker T, Hu HL, Koelle DM, et al. Famciclovir for the suppression of symptomatic and asymptomatic herpes simplex virus reactivation in HIVinfected persons. A double-blind, placebo-controlled trial. Ann Intern Med. 1998; 128(1):21-28.
70 Spruance SL, Jones TM, Blatter MM, et al. High-dose, short-duration, early valacyclovir therapy for episodic treatment of cold sores: results of two
randomized, placebo-controlled, multicenter studies. Antimicrob Agents Chemother. 2003; 47(3):1072-1080.
71 Miller CS, Cunningham LL, Lindroth JE, et al. The efficacy of valacyclovir in preventing recurrent herpes simplex virus infections associated with dental
procedures. J Am Dent Assoc. 2004; 135(9):1311-1318.
72 Klassen TP, Belseck EM, Wiebe N, et al. Acyclovir for treating varicella in otherwise healthy children and adolescents. Cochrane Database Syst Rev.
2005; (4):CD002980.
73 Lebrun-Vignes B, Bouzamondo A, Dupuy A, et al. A meta-analysis to assess the efficacy of oral antiviral treatment to prevent genital herpes outbreaks.
J Am Acad Dermatol. 2007; 57(2):238-246.
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Antivirals, Influenza
Therapeutic Class Review (TCR)
February 27, 2012
No part of this publication may be reproduced or transmitted in any form or by any means, electronic
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Attention: Copyright Administrator
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The materials contained herein represent the opinions of the collective authors and editors and should
not be construed to be the official representation of any professional organization or group, any state
Pharmacy and Therapeutics committee, any state Medicaid Agency, or any other clinical committee.
This material is not intended to be relied upon as medical advice for specific medical cases and nothing
contained herein should be relied upon by any patient, medical professional or layperson seeking
information about a specific course of treatment for a specific medical condition. All readers of this
material are responsible for independently obtaining medical advice and guidance from their own
physician and/or other medical professional in regard to the best course of treatment for their specific
medical condition. This publication, inclusive of all forms contained herein, is intended to be
educational in nature and is intended to be used for informational purposes only. Send comments and
suggestions to [email protected].
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Antivirals, Influenza Review
FDA-APPROVED INDICATIONS
Drug
Manufacturer
amantadine
1,2
(Symmetrel®)
generic
FDA-Approved Indications



oseltamivir (Tamiflu®)
3
Roche



rimantadine
4
(Flumadine®)
zanamivir (Relenza®)
generic


5
GlaxoSmithKline


Prophylaxis and treatment of illness caused by influenza A virus in
adults
Prophylaxis of influenza A in patients older than one year of age
Treatment of idiopathic Parkinson’s disease (Paralysis Agitans),
postencephalitic parkinsonism, and symptomatic parkinsonism
which may follow injury to the nervous system by carbon
monoxide intoxication
Treatment of drug-induced extrapyramidal reactions
Uncomplicated acute illness due to influenza infection in patients
older than one year of age who have been symptomatic for no
more than two days
Prophylaxis of influenza in patients older than one year of age
There is no evidence for efficacy of oseltamivir in any illness
caused by agents other than influenza virus A and B.
Efficacy of oseltamivir in patients who begin treatment after
more than 48 hours of symptoms has not been established.
Prophylaxis and treatment of illness caused by influenza A virus in
adults (≥ 17 years older)
Prophylaxis of influenza A in patients older than one year of age
(ages one to 16 years)
Treatment of uncomplicated acute illness due to influenza A or B
virus in adults and pediatric patients seven years and older who
have been symptomatic for no more than two days
Prophylaxis of influenza in patients older than five years of age
Not recommended for treatment or prophylaxis for influenza
for patients with underlying airways diseases due to risk of
bronchospasm
Not proven effective for treatment in patients with underlying
airways diseases
Not proven effective for prophylaxis of influenza in nursing
home residents
All antivirals for the treatment of influenza should be started as soon as possible and within 48 hours
after illness onset to maximize the potential benefit of reducing duration of illness by one to two days.
Influenza viruses change over time. Emergence of drug resistance could decrease drug effectiveness.
Prescribers should consider the most current available drug susceptibility information on influenza and
treatment effects when deciding whether to use antiviral therapy.
Antiviral treatment for influenza is not a substitute for annual vaccination for influenza.
OVERVIEW
Influenza is a common illness affecting most people at least once in their lifetime. Influenza is most
often self-limiting; however, very young, old, or immunocompromised patients are predisposed to
secondary complications with potential fatalities. Symptoms include abrupt onset of fever, myalgia,
headache, malaise, and respiratory signs and symptoms including nonproductive cough, sore throat,
and rhinitis.6,7 Children may also experience otitis media, nausea, and vomiting. Uncomplicated
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Antivirals, Influenza Review
influenza illness typically resolves after three to seven days for most patients; however, cough and
malaise can persist for more than two weeks.
In 2009 to 2010, a novel influenza A (H1N1) virus (swine flu) garnered much attention worldwide. 8
World Health Organization (WHO) elevated the pandemic to Phase 6, indicating the virus achieved
widespread human infection.9 In August 2010, WHO announced that pandemic H1N1 influenza is in the
post-pandemic period when local sporadic outbreaks may still occur.10
Vaccination
Influenza vaccination is the primary method for preventing influenza and the severe complications.11
The Advisory Committee on Immunization Practices (ACIP) recommendations for the 2010-2011
influenza season recommend an annual influenza vaccination for all people age six months and older. 12
In late August, the CDC announced the vaccine viral strain composition for the 2011-2012 influenza
season is identical to those contained in the 2010-2011 vaccines.13
Treatment
Centers for Disease Control and Prevention (CDC) issued updated recommendations for the use of
antivirals in the treatment and prevention of influenza for the 2011-2012 season.14,15 While viruspositive tests have been reported in all 50 states since, influenza activity started to increase slowly
during December of 2011. The CDC defines the beginning of the influenza season as the time when
greater than ten percent of tested respiratory specimens are positive for influenza. The ten percent
threshold was not exceeded until the week ending February 4, 2012. In the week ending February 15,
2012, the CDC reported the percentage of specimens testing positive was 15 percent.16
The primary viral strain reported for this season has been influenza A (H3N2), although pH1N1 and
influenza B viruses have also been identified. The relative percentages of each viral type varies by date
and region, however, the pH1N1 viruses have been on the increase in recent weeks, particularly in the
southern regions of the United States.17
Studies indicate that early antiviral treatment can reduce the risk of complications from influenza, such
as pneumonia, respiratory failure, and death. Antiviral treatment is recommended as early as possible
for any patient with confirmed or suspected influenza who has severe, complicated, or progressive
illness; is hospitalized; or is at high risk for influenza complications. Patient groups at high risk for
influenza complications include children younger than two years of age; adults 65 years of age and
older; people with chronic pulmonary (including asthma); cardiovascular (except hypertension); renal;
hepatic; hematological (including sickle cell disease); neurological and neurodevelopmental conditions
[including disorders of the brain, spinal cord, peripheral nerve, and muscle such as cerebral palsy,
epilepsy (seizure disorders), stroke, intellectual disability (mental retardation), moderate to severe
developmental delay, muscular dystrophy, or spinal cord injury]; or metabolic disorders (including
diabetes mellitus); immunosuppression, including that caused by medications or by HIV infection;
women who are pregnant or post-partum (within two weeks after delivery); people younger than 19
years of age who are receiving long-term aspirin therapy; American Indians and Alaskan Natives;
people who are morbidly obese (body-mass index ≥40); and residents of nursing homes and other
chronic-care facilities. Clinical judgment, based on the patient's disease severity and progression, age,
underlying medical conditions, likelihood of influenza, and time since onset of symptoms, is important
to consider when making antiviral treatment decisions for high-risk outpatients.
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Antivirals, Influenza Review
When indicated, antiviral treatment should be started as soon as possible after illness onset. Studies
show that treatment initiated early (e.g., within 48 hours of illness onset) is more likely to provide
benefit. Treatment should not wait for laboratory confirmation of influenza because a negative rapid
test for influenza does not rule out influenza. Treatment with oseltamivir (Tamiflu) or zanamivir
(Relenza) is recommended for all people with suspected or confirmed influenza according to approved
ages and dosages. Antiviral treatment also can be considered for any previously healthy, non-high-risk,
symptomatic outpatient with confirmed or suspected influenza based upon clinical judgment, if
treatment can be initiated within 48 hours of illness onset.
Prophylaxis
According to the CDC, antiviral chemoprophylaxis generally should be reserved for people at higher risk
for influenza-related complications who have had contact with someone likely to have been infected
with influenza.18 The infectious period for influenza is defined as one day before until 24 hours after
fever ends. Children can shed influenza viruses for longer periods. Antivirals are not generally
recommended if more than 48 hours have elapsed since the last contact with an infectious person.
Antiviral chemoprophylaxis is not appropriate for healthy children or adults based on potential
exposure in the community. Influenza vaccination should be the primary method of prevention, when
possible, rather than chemoprophylaxis with antiviral medications.
An emphasis on early treatment and monitoring is an alternative to chemoprophylaxis after a
suspected exposure for some people. Prophylaxis may be considered for the following patient groups:
people at high risk of influenza complications during the first two weeks following vaccination after
exposure to an infectious person; people with severe immune deficiencies or others who might not
respond to influenza vaccination, such as people receiving immunosuppressive medications, after
exposure to an infectious person; people at high risk for complications from influenza who cannot
receive influenza vaccine due to a severe egg allergy or other contraindication after exposure to an
infectious person; and residents of institutions, such as long-term care facilities, during influenza
outbreaks in the institution.
PHARMACOLOGY
Drug Mechanism
of Action
amantadine
19
(Symmetrel)
oseltamivir
20
(Tamiflu)
rimantadine
21
(Flumadine)
zanamivir
22
(Relenza)
Mechanism of Action






Amantadine is thought to prevent the release of infectious viral nucleic acid into the host cell and
may also interfere with the viral penetration into cells. Amantadine is also known to prevent
virus assembly during virus replication.
It is active against the influenza A virus, but not influenza B.
Oseltamivir is a prodrug that is converted to the active form, oseltamivir carboxylate. It inhibits
influenza virus neuraminidase with the possibility of alteration of virus particle aggregation and
release. Oseltamivir is active against influenza A and B viruses.
Rimantadine appears to exert its inhibitory effect early in the viral replication cycle, possibly
inhibiting the uncoating of the virus.
It is active against the influenza A virus, but not influenza B.
Zanamivir inhibits influenza virus neuraminidase with the possibility of alteration of virus particle
aggregation and release. Zanamivir is active against influenza A and B viruses.
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Antivirals, Influenza Review
Viral Resistance
Influenza viral resistance has been documented following treatment with zanamivir and
oseltamivir.23,24 In vitro viral cross-resistance between oseltamivir (Tamiflu) and zanamivir (Relenza)
has been identified; however, the incidence and extent of clinical cross-resistance is difficult to
determine.
High levels of resistance (93 percent) of influenza A virus to amantadine and rimantadine have been
observed in the US in 2005-2006.25 The CDC monitors viral resistance and responds to changes in
resistance by publishing recommendations based on the incidence of viral resistance. 26 In past years
such as the influenza season of 2007-2008, 98.9 percent of influenza A (H3N2) viruses and 4.7 percent
of influenza A (H1N1) viruses were resistant to the adamantanes. Over the last few years, emerging
influenza A strains were showing increasing resistance to oseltamivir.
Oseltamivir-resistant strains of 2009 H1N1 influenza have been identified in the United States in
2009.27 The mutation of these viruses shows the H275Y mutation that confers resistance to the
antiviral oseltamivir, but not to the antiviral zanamivir. According to WHO, the risk of viral resistance is
considered higher in patients with severely compromised or suppressed immune systems who have
prolonged illness, have received oseltamivir treatment (especially for an extended duration), but still
have evidence of persistent viral replication.28 The risk of resistance is also considered higher in people
who receive oseltamivir for post-exposure prophylaxis and who then develop illness despite taking
oseltamivir. No evidence exists that oseltamivir-resistant viruses are causing different or more severe
form of illness. Since October of 2011 a total of 426 influenza specimens have been tested to
determine antiviral resistance. For the 309 influenza A (H3N2), 71 pH1N1 and 46 influenza B isolates,
100 percent have been susceptible to both oseltamivir and zanamivir while high levels of resistance to
both amantadine and rimantadine continue for pH1N1 and influenza (H3N2) viruses currently
identified.29
Susceptibilities as of February 24, 2012 according to CDC30
Influenza type
oseltamivir
amantadine and
rimantadine
zanamivir
Pandemic (H1N1) 2009
Susceptible
Susceptible
Resistant
Seasonal A (H3N2)
Susceptible
Susceptible
Resistant
Influenza B
Susceptible
Susceptible
no activity
PHARMACOKINETICS
Drug
amantadine
31,32
(Symmetrel)
oseltamivir (Tamiflu)
Half-Life
(hr)
Metabolism
Excretion
86-94
9-31
Eight metabolites
Predominantly renal
75
1-3 (parent);
6-10 (metabolite)
One active -- oseltamivir
carboxylate
Predominantly renal
--
13-65
At least four metabolites
Hepatically metabolized,
metabolites renally
excreted
4-17
2.5-5.1
No metabolites
Renally excreted
33
rimantadine
34
(Flumadine)
zanamivir (Relenza)
Bioavailability (%)
35
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Antivirals, Influenza Review
CONTRAINDICATIONS/WARNINGS
Cross-hypersensitivity between rimantadine and amantadine is possible and is a contraindication for
use.36
Amantadine overdoses in suicide attempts have been associated with death with 1 gm as the lowest
lethal dose reported.37 Amantadine may exacerbate mental problems in patients with a history of
psychiatric disorders or substance abuse. Patients who attempt suicide may exhibit abnormal mental
states which include disorientation, confusion, depression, personality changes, agitation, aggressive
behavior, hallucinations, paranoia, other psychotic reactions, and somnolence or insomnia. Patients
with a history of epilepsy or other seizures should be observed closely for possible increased seizure
activity while on amantadine. Patients with a history of congestive heart failure or peripheral edema
should be followed closely as there is a risk for the development of congestive heart failure while
receiving amantadine. Amantadine has anticholinergic effects and may cause mydriasis; therefore,
patients with untreated angle closure glaucoma should not receive amantadine.
Rimantadine has been associated with an increase in seizure activity for patients who have a history of
seizure activity.38 Patients with renal or hepatic insufficiency should be closely observed for signs of
adverse effects when taking rimantadine due to an accumulation of the parent drug and its
metabolites. Transmission of rimantadine resistant virus should be considered when treating patients
whose contacts are at high risk for influenza A illness. Influenza A virus strains resistant to rimantadine
can emerge during treatment, and such resistant strains have been shown to be transmissible and to
cause typical influenza illness. Serious bacterial infections may begin with influenza-like symptoms or
may coexist with or occur as complications during the course of influenza. Rimantadine has not been
shown to prevent such complications.
Zanamivir (Relenza) should not be used in patients with a history of allergic reaction to any component
of zanamivir including lactose (contains milk proteins).39 Zanamivir is not recommended for treatment
or prophylaxis of influenza in individuals with underlying airway diseases such as asthma or chronic
obstructive pulmonary disease due to risk of serious bronchospasm. Zanamivir should be discontinued
in any patient who develops bronchospasm or respiratory difficulty. Effectiveness of prophylaxis of
influenza in the nursing home setting has not been established. Allergic-like reactions, including
oropharyngeal edema, serious skin rashes, and anaphylaxis have been reported in postmarketing
experience with zanamivir. There is no evidence for efficacy of zanamivir in an illness caused by
infectious agents other than influenza A or B. Patients should be advised that the use of zanamivir for
the treatment of influenza has not been shown to reduce the risk of transmission of influenza to others
nor has zanamivir been proven to prevent serious complications including serious bacterial infections.
Zanamivir must not be made into an extemporaneous solution for administration by nebulization or
mechanical ventilation. Zanamivir inhalation powder must only be administered using the device
provided.
Oseltamivir (Tamiflu) is contraindicated in patients with known serious hypersensitivity to oseltamivir
or any component of the product. Severe allergic reactions have included anaphylaxis and serious skin
reactions including toxic epidermal necrolysis, Stevens-Johnson Syndrome, and erythema multiforme.
Efficacy of oseltamivir in the treatment of influenza has not been established in patients with chronic
cardiac disease and/or respiratory disease.40 No difference in the incidence of complications was
observed between the treatment and placebo groups in this population. No information is available
regarding treatment of influenza in patients with any medical condition sufficiently severe or unstable
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Antivirals, Influenza Review
to be considered at imminent risk of requiring hospitalization. Efficacy of oseltamivir for treatment or
prophylaxis of influenza has not been established in immunocompromised patients. Serious bacterial
infections may begin with influenza-like symptoms or may co-exist or occur as complications during the
course of influenza. Oseltamivir has not been shown to prevent these complications.
Neuropsychiatric Reactions41.42
Hallucinations, delirium and abnormal behavior have been reported with influenza infection.
Neuropsychiatric reactions have been noted in post-marketing surveillance of oseltamivir and
zanamivir. Reports including those with fatal outcomes have described self-injury and delirium in
mostly pediatric patients on oseltamivir or zanamivir with influenza. Event reports in pediatric patients
have noted abrupt onset and rapid resolution of neuropsychiatric events. Unusual behavior should be
reported to a healthcare professional promptly. If neuropsychiatric events occur, the risks and benefits
of continuing treatment should be evaluated.
Drug Interactions43,44,45,46
Amantadine undergoes enhanced elimination with coadministration of urine acidifying drugs.
Coadministration of quinine or quinidine with amantadine was shown to reduce the renal clearance of
amantadine by approximately 30 percent. Agents with anticholinergic effects may potentiate the
anticholinergic adverse effects of amantadine. Administration of amantadine with thioridazine can
cause increased tremor in elderly patients with Parkinson’s disease.
Administration of agents in this class with Influenza Virus Vaccine Live (FluMist®) has not been
evaluated. Because of the potential interference between the antivirals and FluMist, it is advisable that
FluMist not be administered until 48 hours after cessation of anti-influenza antiviral therapy. Antiinfluenza antivirals should not be administered until two weeks after the FluMist vaccine
administration unless medically necessary. Trivalent inactivated influenza vaccine can be administered
at any time relative to use of drugs in this category.
No other drug interactions are expected with zanamivir or oseltamivir.
ADVERSE EFFECTS
Drug
amantadine (Symmetrel)
oseltamivir (Tamiflu)
75 mg twice daily
n=724 adults;
placebo n=716
47
Headache
Nausea
Dizziness
Abd. Pain
Vomiting
Diarrhea
1-5
5-10
5-10
nr
0.1-1
1-5
2
(2)
10
(6)
2
(3)
2
(2)
9
(3)
7
(10)
1.4
(1.3)
2.8
(1.6)
1.9
(1.1)
1.4
(0.8)
1.7
(0.6)
0.3-1
2
(3)
3
(3)
2
(<1)
<1.5
1
(2)
3
(4)
48
rimantadine (Flumadine)
n=1,027
49
50
zanamivir (Relenza)
10 mg twice daily
n=1,132 adults; placebo
n=1,520
Adverse effects are reported as a percentage. Adverse effects data are obtained from prescribing information and are not
meant to be comparative or all inclusive. Incidences for the placebo group are indicated in parentheses. nr = not reported.
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In the treatment of influenza, vomiting was the most common adverse effect in children receiving
oseltamivir (15 percent versus nine percent in the placebo group).51 Vomiting is also the most common
adverse event in children undergoing prophylaxis for influenza with oseltamivir. Oseltamivir may be
administered with or without food, however, drug tolerability may be increased for certain patients if
taken with food.52
The most common adverse effect in children receiving zanamivir was ear, nose, and throat infections.
These occurred at a rate of five percent for both zanamivir-treated and placebo-treated patients.53
Amantadine may also cause other adverse events such as insomnia, hallucinations, confusion,
orthostatic hypotension, peripheral edema, and dry mouth.54
SPECIAL POPULATIONS55,56,57,58
Pediatrics
For the treatment and prophylaxis of uncomplicated influenza A viral infections, amantadine is
indicated for children as young as one year old. Rimantadine is indicated for the prophylaxis of
influenza A infections in children ages one year to 16 years old, however, treatment with rimantadine
is limited to patients age 17 years and older.
Early empiric treatment with oseltamivir (Tamiflu) or zanamivir (Relenza) should be considered for
people with suspected or confirmed influenza who require hospitalization and/or have progressive,
severe, or complicated illness, regardless of previous health status, and/or with risk factors for severe
illness.59 The risk factors for severe illness, according to the CDC, are the same medical conditions in
adults and in children. Children less than five years of age are at higher risk for complications
secondary to 2009 H1N1 influenza, especially children less than two years of age. According to the
American Academy of Pediatrics, children at higher risk for complications related to influenza infection
include those with neurological disorders, chronic respiratory diseases, moderate to profound
intellectual disability or developmental delay, deficiencies in immune function or conditions which
require medications or treatments that result in significant immune deficiencies, sickle cell anemia and
other hemoglobinopathies, hemodynamically significant heart disease, asthma or other chronic
pulmonary diseases including cystic fibrosis, conditions that can compromise respiratory function or
handling of secretions or can increase the risk of aspiration, chronic renal dysfunction, long-term
aspirin therapy including juvenile idiopathic arthritis or Kawasaki disease, or significant metabolic
disorders including diabetes mellitus.60
Zanamivir has been approved for prevention of influenza in children as young as five years and is
approved for the treatment of influenza for children ages seven years and older. The limitation of
zanamivir is the dose administration technique of the inhaler.
During the 2009-2010 H1N1 influenza pandemic, emergency use authorization of oseltamivir for
treatment and prophylaxis of 2009 H1N1 influenza was granted by the FDA for children less than one
year of age.61 The emergency use authorization expired on June 23, 2010. Oseltamivir is not FDAapproved for children less than one year of age. Age-based dosing is recommended, but weight-based
dosing is being considered for some premature or low-weight infants in investigational studies.
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oseltamivir (Tamiflu) versus placebo in children
Oseltamivir was studied in a randomized, double-blind, placebo-controlled trial with 695 children ages
one to 12 years with fever and history of cough or corzya of less than 48 hours of duration. 62 Patients
were randomized to oseltamivir 2 mg/kg twice daily or placebo for five days. Sixty-five percent of
children (n=465) were found to have influenza. Oseltamivir reduced the median duration of illness by
36 hours (26 percent) in the influenza-infected children compared to placebo (101 hours versus 137
hours, p<0.0001). Oseltamivir reduced cough, corzya, and duration of fever. New diagnoses of acute
otitis media were also reduced in the oseltamivir group (12 versus 21 percent, respectively). Use of
antibiotics was significantly lower in the influenza-infected oseltamivir group compared to the
influenza-infected placebo group (31 versus 41 percent, respectively, p=0.03). Oseltamivir group
experienced more emesis than placebo group.
In a randomized, double-blind, placebo-controlled study, the efficacy of oseltamivir initiated within 24
hours of symptom onset in 408 children ages one to three years was evaluated.63 Patients (n=98) had
laboratory-confirmed influenza during the 2007-2008 or 2008-2009 influenza seasons in Finland.
Patients received oseltamivir suspension or placebo twice daily for five days. For the patients initiating
oseltamivir within 12 hours of symptom onset (secondary outcome measure), oseltamivir decreased
the incidence of acute otitis media by 85 percent (95% CI, 25-97). No significant reduction in AOM was
observed in the group of patients who initiated therapy within 24 hours of symptom onset, the primary
endpoint. For patients with influenza A (n=79), oseltamivir initiated within 24 hours of symptom onset
shortened the median time to resolution of illness by 3.5 days (three days versus 6.5 days; p=0.006) in
all children and by four days (3.4 days versus 7.3 days; p=0.006) in unvaccinated children. Efficacy was
not demonstrated against influenza B infections (n=19).
zanamivir (Relenza) versus placebo in children
A double-blind, randomized, placebo-controlled, parallel-group, multicenter study enrolled children,
five to 12 years of age, with influenza-like symptoms for no more than 36 hours.64 Patients were
randomized to zanamivir 10 mg twice daily or placebo for five days. Symptoms were recorded on diary
cards twice daily during treatment, nine days after treatment, and potentially an additional 14 days if
symptoms persisted. Of the 471 children enrolled in the study, 346 (73 percent) patients were
influenza-positive by culture, serology, or polymerase chain reaction. Of those with confirmed
infection, 65 percent had influenza A and 35 percent had influenza B. Zanamivir reduced the median
time to symptom alleviation by 1.25 days compared with placebo among patients with confirmed
influenza infection (p<0.001). Zanamivir-treated patients returned to normal activities significantly
faster and took significantly fewer relief medications than placebo-treated patients. Zanamivir was
well-tolerated.
PREGNANCY
All agents in this class are Pregnancy Category C.
Pregnant women are at a higher risk for severe complications and death from influenza. In the 2011
recommendations from the CDC, treatment with oseltamivir or zanamivir is recommended for
pregnant women or women who are up to two weeks postpartum (including following pregnancy loss)
with suspected or confirmed influenza.65 Treatment can be given during any trimester of pregnancy.
Oseltamivir is preferred for treatment of pregnant women. Zanamivir might be preferred by some
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Antivirals, Influenza Review
providers because of its limited systemic absorption; however, respiratory complications that might be
associated with zanamivir because of its inhaled route of administration need to be considered,
especially in women at risk for respiratory problems.
Geriatrics
Amantadine accumulates in patients with renal impairment and in patients over age 65 years. Dosage
adjustments are listed in the Dosages section.
Rimantadine elimination is reduced in patients over age 64 years. An increase in central nervous
system and gastrointestinal adverse effects are seen at the standard doses in geriatric patients
receiving 200 or 400 mg of rimantadine. Dosage adjustments are listed in the Dosages section.
No dosage adjustment is required for oseltamivir or zanamivir in the geriatric population.
Renal Impairment
Oseltamivir dose and/or interval should be reduced in patients with an estimated creatinine clearance
of 10-30 mL/minute.
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DOSAGES
Drug/
Dosage Forms
amantadine
66
(Symmetrel)
100 mg tablet;
50 mg/5 mL syrup
oseltamivir
67
(Tamiflu)
30, 45, 75 mg
capsules;
12 mg/1 mL oral
suspension
rimantadine
68
(Flumadine)
100 mg tablet
zanamivir
69
(Relenza)
5 mg diskhaler
Treatment of influenza
Adults
Pediatrics
Prophylaxis of influenza
Adults
Pediatrics
For Influenza A only
1-9 years:
4.4-8.8 mg/kg daily up
1-9 years:
to 150 mg daily
4.4-8.8 mg/kg daily up to
200 mg daily for 10 days 150 mg daily for 10 days
9-12 years:
(>12 years)
Therapy to continue for
100 mg twice daily
9-12 years:
24-48 hours after
100
mg
twice daily for 10
Therapy to continue for
resolution of signs and
days
24-48 hours after
symptoms
resolution of signs and
symptoms
For Influenza A only
200 mg daily
(>12 years)
75 mg twice daily for
five days
(≥13 years)
Initiate therapy within 2
days of onset of
symptoms.
For Influenza A only
100 mg twice daily
for seven days (≥17
years)
>1 to <13 years:
< 15 kg: 30 mg twice
daily;
15-23 kg: 45 mg twice
daily;
23-40 kg: 60 mg twice
daily;
> 40 kg: 75 mg twice
daily
--
>1to < 13 years:
< 15 kg: 30 mg daily for
10 days;
15-23 kg: 45 mg daily for
10 days;
75 mg daily for 10 days
23-40 kg: 60 mg daily for
(≥13 years)
10 days;
Initiate therapy within 2 > 40 kg: 75 mg daily for
days of exposure.
10 days
May give for up to six
weeks for community
outbreak.
100 mg twice daily
(≥17 years)
1 to 9 years:
5 mg/kg daily up to 150
mg daily
For 10 to 16 years of age,
use adult dosage
≥5 years:
Two inhalations (10 mg)
Two inhalations (10 mg)
Two inhalations (10 mg)
twice daily for 5 days
once daily for 10 days
≥7 years:
once daily for 10 days
Two
inhalations
(10
mg)
(household
setting) or
Initiate therapy within 2
(household setting) or 28
twice daily for 5 days
28 days (community
days of onset of
days (community
outbreaks)
symptoms.
outbreaks)
Amantadine is given as 100 mg twice daily for Parkinsonism and drug-induced extra-pyramidal
reactions.
Patients scheduled to use an inhaled bronchodilator at the same time as zanamivir should use their
bronchodilator before taking zanamivir.
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DOSAGE ADJUSTMENTS
Treatment of influenza
Drug/
Dosage Forms
amantadine
70
(Symmetrel)
Disease
state/concurrent
condition
Recommended
dosage adjustment
Disease
state/concurrent
condition
Recommended
dosage adjustment
Patients > 65 years
Consider dose reduction
for the following:
Congestive heart failure,
peripheral edema,
orthostatic hypotension
100 mg daily or 50 mg
twice daily
Patients > 65 years
Consider dose reduction
for the following:
Congestive heart failure,
peripheral edema,
orthostatic hypotension
100 mg daily or 50 mg
twice daily
CrCl 30-50
2
mL/min/1.73m
200 mg on first day and
100 mg each day
thereafter
CrCl 30-50
2
mL/min/1.73m
200 mg on first day and
100 mg each day
thereafter
CrCl 15-29
2
mL/min/1.73m
200 mg on first day
followed by 100 mg on
alternate days
CrCl 15-29
2
mL/min/1.73m
200 mg on first day
followed by 100 mg on
alternate days
200 mg every seven
days
CrCl <15 mL/min/1.73m
and hemodialysis
CrCl <15 mL/min/1.73m
and hemodialysis
oseltamivir
71
(Tamiflu)
rimantadine
zanamivir
73
(Relenza)
Prophylaxis of influenza
2
2
200 mg every seven
days
75 mg every other day
75 mg once daily for five
or 30 mg once daily for
days
10 days
Severe renal impairment
Severe renal impairment
No recommendations
(estimated CrCl 10-30
(estimated CrCl 10-30
No recommendations
are available for patients
mL/min
mL/min
are available for patients
with ESRD on
with ESRD on
hemodialysis or CAPD
hemodialysis or CAPD
72
Severe hepatic
dysfunction
Renal insufficiency (CrCI
5 to 29 mL/min)
Renal failure (CrCI≤10
mL/min)
Elderly nursing home
patients
100 mg daily
Severe hepatic
dysfunction
Renal insufficiency (CrCI
5 to 29 mL/min)
Renal failure (CrCI≤10
mL/min)
Elderly nursing home
patients
100 mg daily
Not recommended for patients with airway diseases such as chronic obstructive pulmonary disease
and asthma
CrCl = creatinine clearance; ESRD = end stage renal disease; CAPD = continuous ambulatory peritoneal dialysis
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CLINICAL TRIALS
Studies were identified through searches performed on PubMed and review of information sent by
manufacturers. Search strategy included the FDA-approved use of all drugs in this class. Randomized,
controlled trials performed in the United States comparing oral and inhaled agents within this class in
an outpatient setting for the approved indications are considered the most relevant in this category.
Due to changes in resistance and practice patterns over time, studies conducted more than ten years
ago were excluded. Because of the paucity of active controlled trials of the antiviral agents used for
treatment and prophylaxis of influenza, studies that were placebo-controlled, randomized trials in
humans using antiviral agents for the treatment or prevention of influenza were included. Studies
included for analysis in the review were published in English, performed with human participants and
randomly allocated participants to comparison groups. In addition, studies must contain clearly stated,
predetermined outcome measure(s) of known or probable clinical importance, use data analysis
techniques consistent with the study question and include follow-up (endpoint assessment) of at least
80 percent of participants entering the investigation. Despite some inherent bias found in all studies
including those sponsored and/or funded by pharmaceutical manufacturers, the studies in this
therapeutic class review were determined to have results or conclusions that do not suggest
systematic error in their experimental study design. While the potential influence of manufacturer
sponsorship/funding must be considered, the studies in this review have also been evaluated for
validity and importance.
Influenza - Treatment
oseltamivir (Tamiflu) versus placebo
A randomized, double-blind study was performed in 629 healthy nonimmunized adults in the United
States with febrile illness of less than 36 hours duration.74 Patients were randomized to receive
oseltamivir 75 mg or 150 mg or matching placebo twice daily. In the 374 patients infected with
influenza, median duration of illness was shorter in the oseltamivir 75 mg (71.5 hours; p<0.001 versus
placebo) and 150 mg groups (69.9 hours; p=0.006 versus placebo) compared to placebo (103.3 hours).
There was no difference observed between the two active treatment regimens. Secondary
complications such as bronchitis and sinusitis occurred more frequently in the placebo group (15
percent) than the oseltamivir groups (seven percent; p=0.03). Additionally, oseltamivir-treated patients
returned to usual activities two to three days earlier than placebo-treated patients (p≤0.05). Nausea
and vomiting occurred more frequently in the oseltamivir groups (combined incidence of 18 and 14.1
percent, respectively; p=0.002) compared to placebo (7.4 and 3.4 percent; p<0.001).
A randomized, double-blind, controlled trial was conducted in 726 previously healthy nonimmunized
adults with febrile influenza-like illness of up to 36 hours duration.75 Patients were assigned to
oseltamivir 75 mg, oseltamivir 150 mg, or placebo twice daily for five days. Infection was confirmed in
66 percent of patients. Compared to placebo (median duration 116.5 hours), the duration of illness,
the primary endpoint, was 29 hours shorter in the oseltamivir 75 mg group (median duration 87.4
hours; p=0.02) and 35 hours shorter in the oseltamivir 150 mg group (median duration 81.8 hours;
p=0.01). The effect of oseltamivir was apparent within 24 hours of the start of treatment. In patients
treated within 24 hours of symptom onset, symptoms were alleviated in 74.5 hours in the oseltamivir
75 mg group, in 70.7 hours in the oseltamivir 150 mg group and in 117.5 hours in the placebo group
(p≤0.02 for both active treatments compared to placebo). Oseltamivir was associated with lower
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Antivirals, Influenza Review
symptom scores, less viral shedding, and improved health, activity, and sleep quality. Oseltamivir was
well tolerated.
zanamivir (Relenza) versus placebo
In a double-blind trial, 417 adults with influenza-like illnesses of less than 48 hours duration were
randomized to zanamivir 6.4 mg intranasal spray plus 10 mg by inhalation, zanamivir 10 mg inhalation
plus placebo spray, or placebo by both routes twice daily for five days.76 Sixty-three percent of patients
(n=262) had confirmed influenza virus infection. In the confirmed influenza infections, the median
length of time to alleviation of all symptoms was one day shorter (four versus five days) in the group
given both zanamivir doses (p=0.02) and for those patients receiving inhalation zanamivir (p=0.05)
compared to those on both placebo doses. For patients initiating therapy within 30 hours of onset of
symptoms, the resolution of symptoms with either of the zanamivir groups was significantly earlier
than the placebo group (four days versus seven days, p≤0.01).
A randomized, double-blind, placebo-controlled study was conducted in 455 patients aged 12 years
and older with influenza-like symptoms of less than 36 hours.77 Patients were randomly assigned to 10
mg inhaled zanamivir (n=227) or placebo (n=228) twice daily for five days. Patients were asked to
record symptoms on diary cards four times daily during treatment and twice daily for nine days after
treatment. Zanamivir relieved influenza symptoms a median of 1.5 days earlier in the intention-to-treat
(p=0.011) and influenza-positive populations (p=0.004), and two days earlier in patients who were
febrile at entry. In high-risk patients treated with zanamivir, symptoms were alleviated a median of 2.5
days earlier (p=0.048), fewer had complications (p=0.004), and fewer used complication-associated
antibiotics (p=0.025) compared with placebo. Adverse event profiles were similar for zanamivir and
placebo.
In a double-blind trial, 27 otherwise healthy adult patients were randomized to zanamivir 10 mg twice
daily for five days or matching placebo.78 Treatment was started within the first or second day of a flulike illness. After 12 hours of treatment (e.g., one dose), median virus titers changed by -1.0 log10
TCID50/mL in the zanamivir group compared with +0.42-log10 change in the placebo group (p=0.08).
This was associated with a 4.5 day (47.4 percent) reduction in the median time to alleviation of all
significant flu symptoms in the zanamivir recipients (p=0.03 after adjusting for the initial virus titer and
the time between onset of symptoms and treatment). Resistance to zanamivir was not detected in
virus isolates.
In a randomized, double-blind trial, 356 patients aged 12 years and older were recruited within two
days of onset of typical influenza symptoms.79 Patients were randomized to receive inhaled zanamivir
10 mg twice daily for five days or matching placebo. Influenza was laboratory-confirmed in 277 (78
percent) of the patients; 32 (nine percent) patients were considered high-risk (elderly or with
underlying medical conditions). The primary endpoint, time to alleviation of clinically significant
symptoms of influenza, was significantly reduced by zanamivir compared to placebo (5 and 7.5 days,
respectively; p<0.001). Zanamivir was well tolerated.
oseltamivir (Tamiflu) and zanamivir (Relenza)
Although the study was conducted in an open-label manner, it has been included due to a lack of other
direct comparative data. In a Japanese study, the effectiveness of zanamivir with oseltamivir for
influenza A and B were compared in 1,113 patients during the 2006-2007 influenza season.80 The
duration of fever (≥ 37.5o C) after the first dose was less with zanamivir (31.8 hrs) compared to
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oseltamivir (35.5 hours; p<0.05) in patients with influenza A. For patients with influenza B, fever
duration after starting zanamivir therapy (35.8 hrs) was significantly shorter than that of oseltamivir
(52.7 hrs; p<0.001). By multiple regression analysis, therapy (zanamivir or oseltamivir) was the major
determinant affecting the duration of fever for influenza B.
Influenza - Prophylaxis
oseltamivir (Tamiflu) versus placebo
A study compared the efficacy of oseltamivir in prevention of household contacts acquiring influenza
from the index case. A total of 955 household contacts of people with influenza were enrolled in a
preventative, double-blind study and randomized to oseltamivir 75 mg once daily or placebo for seven
days.81 Randomization occurred by household within 48 hours of symptom onset of the index case of
influenza. The index case patients did not receive therapy in the study. The overall protective efficacy
of oseltamivir against clinical influenza was 89 percent for individuals (95% confidence interval [CI], 6797 percent; p<0.001) and 84 percent for households (95% CI, 49-95 percent; p<0.001). Gastrointestinal
adverse events were similar in both groups (oseltamivir, 9.3 percent; placebo, 7.2 percent).
In a double-blind, placebo-controlled, parallel-group, multicenter study, 548 frail, elderly nursing home
occupants (mean age 81 years, >80 percent vaccinated for influenza) were randomized to prophylaxis
with oseltamivir 75 mg or placebo once daily for six weeks, beginning when influenza was detected
locally.82 The administration of oseltamivir resulted in a 92 percent reduction in the incidence of
laboratory-confirmed clinical influenza compared with placebo (0.4 and 4.4 percent, respectively;
p=0.002). In vaccinated subjects, influenza was confirmed in 0.5 percent of oseltamivir patients and
five percent of patients randomized to placebo (p=0.003). Oseltamivir use was also associated with a
significant reduction in the incidence of secondary complications (0.4 percent versus 2.6 percent for
placebo; p=0.037). Oseltamivir was well tolerated with a similar incidence of adverse events, including
gastrointestinal effects, occurring in both groups.
Two identical, double-blind, randomized trials located in the US enrolled a total of 1,559 healthy, nonimmunized adults (18 to 65 years old) to receive either oseltamivir 75 mg once or 75 mg twice daily or
placebo for six weeks during the peak of influenza outbreak. 83 For the combined studies, 38 patients
developed influenza-like illness with 19 of those patients having laboratory confirmation. The rate of
influenza was 1.2 and 1.3 percent for the oseltamivir 75 once daily and 75 mg twice daily groups,
respectively, whereas the placebo group had 4.8 percent with influenza (p<0.001 and p=0.001 for
comparison to once daily and twice daily oseltamivir groups, respectively). For the culture-proven
influenza, the rate of protective efficacy was 87 percent for oseltamivir compared to 2.9 percent of the
placebo-treated group (95% CI, 65 to 96 percent, p<0.001). Oseltamivir had more frequent nausea and
vomiting (12.1 and 14.6 for nausea; 2.5 and 2.7 percent for vomiting) compared to placebo of 7.1 and
0.8 percent.
zanamivir (Relenza) versus placebo
A total of 1,107 healthy adults were randomized to receive zanamivir 10 mg once daily or matching
placebo for four weeks in a double-blind manner at the start of the influenza outbreak.84 Zanamivir
was 67 percent efficacious (95% CI, 39 to 83 percent, p<0.001) in preventing laboratory-confirmed
clinical influenza meeting the case definition and 84 percent efficacious (95% CI, 55 to 94 percent;
p=0.001) in preventing laboratory-confirmed illnesses with fever. All influenza infections occurring
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Antivirals, Influenza Review
during the season, with or without symptoms, were prevented with an efficacy of 31 percent (95% CI,
four to 50 percent, p=0.03). Adverse events did not differ between the groups.
Prior to influenza season, 799 families with two to five members and at least one child who was five
years of age or older were enrolled in a double-blind, placebo-controlled study.85 If an influenza-like
illness developed in one member, all family members aged five years and older were randomly
assigned to receive either inhaled zanamivir or placebo. The family member with the index illness was
treated with either zanamivir or placebo twice daily for five days, and the other family members
received either zanamivir or placebo once daily as prophylaxis for ten days. The proportion of families
with at least one initially healthy household contact in whom influenza developed (the primary
endpoint) was significantly lower in the zanamivir group than in the placebo group (four versus 19
percent; p<0.001). Zanamivir provided protection against both influenza A and influenza B. Among the
subjects with index cases of laboratory-confirmed influenza, the median duration of symptoms was 2.5
days shorter in the zanamivir group than in the placebo group (5 versus 7.5 days; p=0.01). Viral
resistance to zanamivir was not identified in this study. Zanamivir was well tolerated.
After close contacts with index cases of influenza-like illnesses, 575 subjects were randomized to
receive one of four prophylactic regimens in a double-blind manner: placebo, intranasal zanamivir,
inhaled zanamivir and inhaled plus intranasal zanamivir, each given for five days. 86 Of 25 subjects (four
percent) who developed symptomatic influenza during the five days of prophylaxis, nine (36 percent)
were in the placebo group, eight (32 percent) were in the intranasal zanamivir group, three (12
percent) were in the inhaled zanamivir group, and five (20 percent) were in the inhaled plus intranasal
zanamivir group (p=NS for all comparisons to placebo).
A double-blind, randomized study evaluated inhaled zanamivir for the prevention of influenza in
families.87 Once a person with a suspected case of influenza was identified (index patient), treatment
of all other household members (contacts) five years and older was initiated. Contacts received either
10 mg zanamivir or placebo inhaled once daily for 10 days. Index cases were not treated with antivirals
in the trial. In total, 487 households were enrolled with 1,291 contacts randomly assigned to receive
prophylaxis. Four percent of zanamivir versus 19 percent of placebo households had at least one
contact who developed symptomatic, laboratory-confirmed influenza, representing 81 percent
protective efficacy (95% CI, 64 to 90 percent, p<0.001). In the intent-to-treat population, contacts with
laboratory-confirmed influenza were significantly lower in the zanamivir group (seven and 17 percent
for the zanamivir and placebo groups, respectively; 59 percent protective efficacy; 95% CI, 44 to 70,
p<0.001). Protective efficacy was also high for individuals (82 percent) and against both influenza types
A and B (78 and 85 percent, respectively, for households). Zanamivir was well tolerated.
In a multicenter, randomized, double-blind, placebo-controlled, parallel-group study, the efficacy and
safety of zanamivir for the prevention of influenza in community-dwelling patients who were at high
risk for developing complications of influenza were evaluated.88 The study was conducted in the 20002001 influenza season. To be enrolled, patients were able to use the Diskhaler device and were able to
take the first dose of study medication within five days of laboratory-confirmed local influenza activity.
Patients (n=3,363) were randomized to receive inhaled zanamivir 10 mg or placebo once daily for 28
days. The proportion of randomized subjects who developed symptomatic influenza during prophylaxis
was significantly lower in those patients receiving zanamivir (4/1,678 versus 23/1,685; relative risk
0.17; [95% CI, 0.07 to 0.44, p<0.001]). Zanamivir provided a protective efficacy of 83 percent.
Significantly fewer complications were observed in the zanamivir-treated patients (1/1,678 versus
8/1,685; relative risk 0.12 [95% CI, 0.002 to 0.73; p=0.042]). Influenza-like illness was reported in nine
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Antivirals, Influenza Review
percent in the zanamivir-treated patients and ten percent in the placebo-treated patients. Adverse
effects were similar between the groups with the most common reports being headache, cough, throat
and tonsil discomfort/pain. The incidences of viral respiratory infections or ear, nose, and throat
infections were similar between the two groups. No resistance to zanamivir was identified in the study.
META-ANALYSES
amantadine and rimantadine89,90,91,92
A systematic review showed that amantadine is superior to placebo in terms of a reduction in duration
of fever for both adults and children, with a decrease in fever duration of one day for adults (MD=0.99; 95% CI: -1.26 to -0.71) and fewer cases of fever for children. No statistically significant difference
was demonstrated between amantadine and placebo in the occurrence of adverse events in the
randomized trials.
The use of rimantadine for the treatment of influenza is based on two systematic reviews. The first
review included three placebo controlled trials of rimantadine in adults and the second review included
one placebo controlled trial of rimantadine in children. Rimantadine is superior to placebo, with a
reduction in duration of fever for adults of greater than one day (MD=-1.24; 95% CI: -1.71 to -0.76) and
fewer cases of fever in children. No statistically significant difference was demonstrated between
rimantadine and placebo in the occurrence of adverse events.
Adults
A 2006 meta-analysis evaluated the prevention and treatment efficacy in symptomatic and
asymptomatic influenza in healthy adults.93 Of the 51 included trials that evaluated either prevention
or treatment of asymptomatic or symptomatic influenza, amantadine prevented 61 percent of the
symptomatic influenza A cases but with a significant discontinuation rate due to adverse effects.94
Rimantadine had fewer data but similar effects. In symptomatic influenza, efficacy rates of oseltamivir
75 mg and 150 mg daily were 61 and 73 percent, respectively whereas zanamivir was 62 percent. For
post-exposure prevention, oseltamivir was associated with 58.5 percent reduction within households
and 68 to 89 percent for contacts of index cases. Symptom duration was shorter by one to two days
with both oseltamivir and zanamivir when therapy was started within 36 to 48 hours of onset. 95
Oseltamivir was associated with nausea. Both oseltamivir and zanamivir reduced nasal viral shedding;
however, amantadine did not. In asymptomatic influenza, antivirals had no effect. Another 2003 metaanalysis found that oseltamivir was associated with a reduction in lower respiratory tract
complications, antibiotic use, and hospitalizations related to influenza in both healthy and at risk
patients.96
A 2009 systematic review included randomized placebo controlled studies of neuraminidase inhibitors
in otherwise healthy adults exposed to naturally occurring influenza.97,98 A total of 20 trials were
included. In the four trials evaluating prophylaxis, the neuraminidase inhibitors had no effect against
influenza-like illness or asymptomatic influenza. The efficacy of oseltamivir 75 mg daily against
symptomatic laboratory confirmed influenza was 61 percent (risk ratio 0.39; 95% CI, 0.18 to 0.85).
Inhaled zanamivir 10 mg daily was 62 percent efficacious (risk ratio 0.38; 95% CI, 0.17 to 0.85). In
postexposure prophylaxis trials, oseltamivir had an efficacy of 58 percent (95% CI, 15 to 79) and 84
percent in two trials of households. Zanamivir performed similarly. For treatment, the hazard ratios for
time to alleviation of influenza-like illness symptoms were in favor of treatment : 1.20 (95% CI, 1.06 to
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Antivirals, Influenza Review
1.35) for oseltamivir and 1.24 (95% CI, 1.13 to 1.36) for zanamivir. Regarding lower respiratory tract
complications, evidence suggests oseltamivir did not reduce influenza related complications (risk ratio
0.55; 95% CI, 0.22 to 1.35).
Children
A systematic review of double-blind, randomized, controlled trials comparing the neuraminidase
inhibitors with placebo in children less than 12 years of age evaluated trials published through 2005. 99
A total of three trials involving 1,500 children with influenza were included with 977 having laboratoryconfirmed influenza. Oseltamivir reduced the median duration of illness by 26 percent (36 hours) in
healthy children with laboratory-confirmed influenza (p<0.0001). The reduction was only 7.7 percent
(10 hours) in 'at risk' or asthmatic children (p=0.54). Zanamivir reduced the median duration of illness
by 24 percent (1.25 days) in healthy children with laboratory-confirmed influenza (p<0.001). No data in
'at risk' children were available. Only oseltamivir produced a significant reduction in the complications
of influenza (particularly otitis media), although there was a trend to benefit for zanamivir. Adverse
events profile of zanamivir was no worse than placebo, but vomiting was more common in children
treated with oseltamivir.
A 2009 systematic review evaluated the effects of the neuraminidase inhibitors in treatment of
children (≤12 years old) with seasonal influenza and prevention of transmission to children in
households.100 Published and unpublished data were considered. A total of four randomized controlled
trials with 1,766 children evaluated treatment with oseltamivir or zanamivir in the community setting
with confirmed or clinically suspected influenza. Three randomized trials with 863 children evaluated
postexposure prophylaxis (one trial for oseltamivir, two trials for zanamivir). The median time to
resolution of symptoms or return to normal activities or both was reduced by 0.5 to 1.5 days, which
was a significant finding in only two trials. A ten day duration of postexposure prophylaxis with
zanamivir or oseltamivir resulted in an eight percent (95% CI, 5 to 12) decrease in the incidence of
symptomatic influenza. Based on only one trial, oseltamivir did not reduce asthma exacerbations and
oseltamivir was not associated with a reduction in overall use of antibiotics (risk difference -0.3, 95%
CI, -0.13 to 0.01). Zanamivir was well tolerated, but oseltamivir was associated with an increased risk of
vomiting (0.05, 95% CI, 0.02 to 0.09, number needed to harm=20).
SUMMARY
Vaccination is the primary method of preventing influenza infection.
Agents approved for influenza prevention and treatment include amantadine (Symmetrel),
rimantadine (Flumadine), oseltamivir (Tamiflu), and zanamivir (Relenza). The CDC currently does not
recommend the use of amantadine or rimantadine for the treatment or prophylaxis of influenza A due
to viral resistance.
The CDC recommends treatment of seasonal influenza in ‘at risk’ adults and children with either
oseltamivir or zanamivir. Treatment should be initiated as early as possible because studies show that
treatment initiated early (e.g., within 48 hours of illness onset) is more likely to provide benefit.
Zanamivir uses a complex administration device for inhalation and should not be used in patients with
pre-existing respiratory disorders. For the treatment of influenza B, either oseltamivir or zanamivir are
recommended.
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Antivirals, Influenza Review
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