Context Influenza virus neuraminidase is thought to be essential for virus replication
in humans; however, to date, available neuraminidase inhibitors are limited
to zanamivir, which is topically administered.
Objective To determine the safety, tolerability, and antiviral activity of oral
neuraminidase inhibitor oseltamivir (GS4104/Ro64-0796) for prevention and
the early treatment of influenza in experimentally infected humans.
Design Two randomized, double-blind, placebo-controlled trials conducted between
June and July 1997.
Setting Individual hotel rooms; 2 large US university medical schools.
Participants A total of 117 healthy adult volunteers (aged 18-40 years; median age,
21 years) who were susceptible (hemagglutination-inhibition antibody titer ≤1:8).
Interventions All subjects were inoculated intranasally with influenza A/Texas/36/91(H1N1)
virus. For the prophylaxis study, oral oseltamivir (100 mg once daily [n=12],
100 mg twice daily [n=12], or matching placebo [n=13], starting 26 hours before
virus inoculation) was administered. For the treatment study, the same drug
was given (20 mg, 100 mg, or 200 mg twice daily, 200 mg once daily, or matching
placebo [n=16], in each group starting 28 hours after inoculation). All regimens
were continued for 5 days.
Main Outcome Measures Comparing placebo groups with pooled treatment groups, for prophylaxis,
outcomes included frequency of infection and viral shedding; for treatment,
viral shedding in titers.
Results In the prophylaxis study, 8 (67%) of 12 placebo and 8 (38%) of 21 oseltamivir
recipients became infected (P=.16; efficacy, 61%);
6 (50%) placebo compared with 0 oseltamivir recipients shed virus (P<.001; efficacy, 100%), and 33% of placebo but no oseltamivir recipient
had infection-related respiratory illness (P<.01).
Among infected subjects in the treatment study (n=69), the viral titer area
under the curve of the combined oseltamivir groups (n=56) was lower (median
[interquartile range {IQR}], 80 [23-151] vs 273 [79-306] log10
tissue culture-infective doses50 per milliliter×hour; P=.02) than the placebo group (n=13), and the median (IQR)
duration of viral shedding with therapy was reduced from 107 (83-131) to 58
(35-59) hours (P=.003). Oseltamivir treatment also
reduced symptom scores (median [IQR] score-hours, 225 [97-349] vs 400 [189-645]; P=.05), and nasal proinflammatory cytokine levels. Transient
mild to moderate nausea after dosing was observed in 15 (17%) of 88 oseltamivir
and 2 (7%) of 29 placebo recipients (95% confidence interval for difference, −11%
to 68%), which was largely prevented by ingestion with food.
Conclusions In these trials, prophylaxis and early treatment with oral oseltamivir
were both associated with significant antiviral and clinical effects in experimental
human influenza.
A continuing need exists for antiviral agents against influenza A and
B virus infections for treatment of influenza and as a supplementation to
vaccines for prevention. The influenza virus neuraminidase is 1 of 2 major
surface glycoproteins of influenza A and B viruses. It cleaves terminal sialic
acid (N-acetylneuraminic acid) residues from cellular
and viral glycoconjugates and is essential for sustained viral replication
in vitro1 and probably also in humans.2 Inhibition of neuraminidase enzymatic action by antibody,
mutation, or chemicals causes virus particles to aggregate at the cell surface
and with each other. In addition, neuraminidase prevents inactivation of influenza
virus by respiratory mucus and likely facilitates infection of the airway
mucosa.3 The enzyme active site is highly conserved
across influenza A and B viruses,4-6
and several novel antiviral compounds have been designed based on the neuraminidase
crystallographic structure.5,7
The neuraminidase inhibitor zanamivir (or GG167) has been shown previously
to have anti-influenza activity in experimentally infected animals7-9 and humans.2 Inhaled zanamivir provides clinical benefit in adults
with acute, uncomplicated influenza.10,11
However, the low oral bioavailability, small volume of distribution, and rapid
renal elimination of zanamivir12 has limited
its administration to topical (intranasal and/or inhaled) routes of delivery
in human studies. These topical routes are not easily used by many patients,
including persons who are infirm and young children, and distribution of the
drug is not uniform throughout the respiratory tract.13
Effective delivery of the drug to both upper and lower respiratory tracts
may be important for reducing complications and viral transmission. Consequently,
considerable interest exists in developing oral inhibitors of influenza neuraminidase.
A carbocyclic transition state analog of sialic acid cleavage, GS4071/Ro64-0802
(3R,4R,5S-4-acetamido-5-amino-3-
[1-ethylpropoxy]-1-cyclohexene-1-carboxylic acid) is comparable with zanamivir in potency and selectivity under in vitro
conditions.14-16
Although GS4071 is poorly absorbed, oral administration of the ethyl ester
prodrug oseltamivir phosphate (GS4104/Ro64-0796) gives good bioavailablity
of GS4071 in multiple species.17 Oral oseltamivir
is active in murine and ferret models of influenza.18,19
In the rat, oral oseltamivir provides prolonged levels of the parent compound
GS4071 in lung tissue and bronchoalveolar lavages.20
In humans, oral oseltamivir is associated with dose-proportional increases
in plasma GS4071 concentrations and a prolonged plasma GS4071 half-life (7-9
hours), which allows for infrequent dosing.21
The objectives of our study were to determine the safety, tolerability, and
antiviral activity of oral oseltamivir for the prevention and early treatment
of influenza in experimentally infected volunteers.
The subjects were healthy adults aged 18 to 40 years who were susceptible
to the challenge virus on the basis of having serum hemagglutination-inhibition
antibody titers with a dilution of 1: 8 or less. Those with concurrent medication
use or illness within 1 week were excluded. Only nonsmokers or those smoking
fewer than 10 cigarettes daily who agreed to abstain during the study were
included. Written informed consent was obtained from each participant in a
form approved by the institutional review boards of the University of Virginia,
Charlottesville, and the University of Rochester, Rochester, NY, and subjects
were compensated for participation.
Using previously described methods,2,22,23
the subjects were isolated in individual hotel rooms 1 day before inoculation
until 8 days after inoculation. They were inoculated by intranasal drops (0.25
mL per nostril) with approximately 106 median tissue culture-infectious
doses (tissue culture-infective doses50) of a safety-tested pool
of influenza A/Texas/36/91(H1N1) virus (provided by the National Institute
of Allergy and Infectious Diseases, Bethesda, Md). This virus was readily
inhibited by GS4071 in Madin Darby canine kidney cells (50% plaque inhibitory
concentration <0.1 µg/mL) and in explants of human respiratory epithelium
(90% yield inhibitory concentration <0.01 µg/mL) in vitro.16
Two randomized, double-blind, placebo-controlled, dose-ranging trials
were conducted in parallel to test the prophylactic and early therapeutic
activity of oral oseltamivir capsules. The placebo capsules were identical
in appearance. In the prophylaxis study (University of Rochester), individual
volunteers were assigned to 1 of 3 treatment groups: 100 mg once daily (n=12),
100 mg twice daily (n=12), or placebo (n=13). Administration began 26 hours
prior to viral inoculation and continued for 5 days. In the treatment study
(University of Virginia), the volunteers were assigned to 1 of 5 treatment
groups (n=16 per group): 20, 100, or 200 mg twice daily, 200 mg once daily,
or placebo. Administration began at 28 hours after inoculation and continued
for 5 days. Because of the large numbers of subjects in the treatment study,
it was conducted in 2 sessions separated by 1 week. Drug was administered
under direct observation of the study nurses to ensure compliance. Computer-generated
code was used to randomize subjects. The code remained unbroken until all
results had been collected and entered into the final database.
Nasal washings were collected before viral inoculation for detecting
respiratory viruses by standard techniques and then each morning for influenza
virus isolation in freshly inoculated Madin Darby canine kidney monolayers.
Washings were also collected each evening on days 2 and 3 after challenge
in the treatment study. Frozen aliquots from samples that were positive on
initial isolation were subsequently titered in Madin Darby canine kidney cells.
Prechallenge and convalescent (3-4 weeks after inoculation) serum samples
were tested for hemagglutination-inhibition antibodies to the challenge virus.
Nasal washings collected before viral inoculation and on days 2, 4,
and 8 after inoculation were processed for cytokine determinations as previously
described.24 Cytokine levels were determined
using commercially available enzyme-linked immunosorbent assay kits and the
manufacturer's protocols. The kits were obtained from the following sources:
interleukin (IL) 5, IL-6, interferon alfa (IFN-α), and IFN-γ (Endogen
Inc, Cambridge, Mass); tumor necrosis factor alpha (TNF-α) (R&D
Systems Inc, Minneapolis, Minn). The limits of sensitivity of these assays,
as supplied by the manufacturers, were as follows: IL-5 (<2 pg/mL), IL-6
(<1 pg/mL), IFN-α (<3 pg/mL), IFN-γ (<2 pg/mL), and TNF-α
(<0.18 pg/mL).
Oral temperatures were recorded 4 times daily, and 14 symptoms (nasal
stuffiness, runny nose, sore throat, sneezing, cough, breathing difficulty,
muscle aches, fatigue, headache, earache/pressure, feverishness, hoarseness,
chest discomfort, overall discomfort) were scored by the subjects twice daily
on a 4-point scale (absent to severe). Rhinorrhea was assessed by measuring
nasal mucus weights; middle-ear pressure abnormalities were assessed by digital
tympanometry completed once daily.23 Routine
safety laboratory studies (complete blood cell counts, differential leukocyte
count, platelets, urinalysis, serum electrolytes, calcium, phosphorus, urea,
creatinine, glucose, total protein, albumin, amylase, uric acid, triglycerides,
cholesterol, aspartate aminotransferase, alanine transaminase, glutamic-oxaloacetic
transaminase, alkaline phosphatase, bilirubin, creatine phosphokinase, and
lactate dehydrogenase) were performed at baseline and following completion
of drug dosing. Acetaminophen was allowed for fever and discomfort.
Infection was defined by a positive culture for influenza virus on 1
or more postinoculation days and/or 4-fold or greater increase in serum hemagglutination-inhibition
antibody titer. Upper respiratory tract illness was defined as 2 or more respiratory
symptoms (nasal stuffiness, runny nose, sore throat, sneezing, hoarseness,
and earache) of moderate or severe intensity occurring on 1 or more days after
challenge. Lower respiratory tract illness was defined by the presence of
cough of moderate or severe intensity on 1 or more days after challenge. Fever
was defined by a confirmed oral temperature of 37.8°C or higher.
In the prophylaxis study, the primary outcomes of interest were the
frequencies of viral shedding and infection. The secondary outcomes were the
symptom scores over time and the frequencies of infection-associated fever
and upper respiratory tract illness. Sample sizes were based on prior findings
with this virus and zanamivir administration.2
With 14 subjects per group, a comparison of placebo vs the pooled active treatments
had an 80% power to detect a significant difference (2-sided, 5% level) between
infection or virus shedding rates of 80% in those taking the placebo vs 30%
taking active drug.
In the treatment study, the primary outcome measure was the quantity
of virus shed over time in nasal washings. This was calculated as an area
under the curve (AUC) for viral titers over the 7 days after treatment initiation.
The secondary efficacy end points included the time to cessation of viral
shedding, total symptom score AUC, nasal mucus weights, frequencies of upper
respiratory tract illness, cough, fever, middle ear pressure abnormalities,
and concentrations of cytokines in nasal lavage fluids. The time to alleviation
of illness was defined as the time from the beginning of the study treatment
to the time that 7 key symptoms typical of natural influenza had reduced to
absent or mild. Similarly, the time to cessation of viral shedding was defined
from the beginning of the study treatment. Sample sizes were based on prior
findings with this virus and zanamivir treatment.2
With 16 subjects per group, a comparison of placebo vs pooled oseltamivir
groups had 80% power to detect a significant difference (2-sided, 5% level)
of 4.0 log10 tissue culture-infective doses50 per milliliter×days
in the viral titer AUCs (SD, 5.5 log10 tissue culture-infective
doses50 per milliliter×days).
A 2-sided Fisher exact test was used for comparison of infection rates
between placebo and the pooled oseltamivir groups and a Wilcoxon rank-sum
test was used to compare differences in viral titer AUC values. The time to
cessation of viral shedding and the time to alleviation of symptoms were compared
using a generalized Gehan-Wilcoxon test. To compare the percentage of subjects
in the placebo group and active dose groups exhibiting gastrointestinal tract
events during the dosing period, exact 95% confidence intervals were calculated
according to the method of Santer and Snell.25
Sample size calculations were performed using statistical software (PASS 6.0,
NCSS, Kaysville, Utah).
The 2 trials enrolled a total of 117 participants, most of whom were
young (median age, 21 years). There were no dropouts and all subjects completed
the full course of drug administration. In the prophylaxis study, 4 subjects
(3 oseltamivir, 1 placebo) were excluded from efficacy analysis because of
baseline hemagglutination-inhibition antibody titers with a dilution of more
than 1: 8. In the treatment study, 11 subjects (8 oseltamivir, 3 placebo)
were excluded because of lack of documented infection or of intercurrent viral
illness (1 oseltamivir) (Figure 1).
All volunteers were included in the analysis of safety.
Among the 12 evaluable placebo recipients, 6 (50%) had recovery of the
challenge virus from nasal washings and 8 (67%) had laboratory-confirmed infection.
In contrast, none of the 21 evaluable oseltamivir recipients had virus isolated
(P<.001; 100% efficacy) and only 8 (38%), 4 in
each dose group, had serologic evidence of infection (P=.16; 61% efficacy). This antiviral effect was associated with reductions
in illness measures. Symptom scores over time did not change significantly
after viral inoculation in the oseltamivir group, in contrast to the expected
peak 2 days after challenge in the placebo group (Figure 2). Infection-associated upper respiratory tract infection
developed in 4 subjects (33%) taking placebo but in none of the subjects taking
oseltamivir (P=.01). Fever was observed in 3 (25%)
and cough in 2 (16%) placebo recipients. No important differences were observed
between the once and twice daily oseltamivir dose groups.
Only the 69 subjects (56 oseltamivir, 13 placebo) with laboratory-documented
infection were included in the analysis of therapeutic efficacy. Drug administration
was initiated at a time when viral titers were increasing (Figure 3). Peak viral titers were observed about 1½ days
after challenge (12 hours after starting study drug) in both groups and tended
to be lower in the oseltamivir recipients. At 24 and 36 hours after initiating
study drugs, the median viral titers were reduced by 2.1 log10
and 3.5 log10, respectively, in the combined oseltamivir group
compared with placebo (P=.02 by AUC analysis). Correspondingly,
the median time to cessation of viral shedding was reduced from 107 hours
in the placebo group to 58 hours in the combined oseltamivir group (P=.003). No significant differences in these virological
measures were observed across the oseltamivir dose groups, although the 200-mg
once daily group had a higher viral titer AUC value compared with the twice
daily dose groups (Table 1).
This antiviral effect was associated with significant reductions in
illness burden and biochemical markers of host inflammatory responses in the
respiratory tract. Total symptom scores peaked at a lower level and resolved
more rapidly in the combined oseltamivir group compared with placebo (Figure 4). The median time to resolution
of illness was 53 hours in the oseltamivir group compared with 95 hours in
the placebo group (P=.03). Nasal mucus weights were
lower by approximately 50% in the oseltamivir group compared with placebo
(P=.02) (Table
1). No important dose-related differences were noted in the principal
clinical outcomes (Table 1). The
frequencies of other measures including upper respiratory tract illness (18%
vs 54%), middle ear pressure abnormalities (28% vs 54%), and fever (14% vs
31%) also were lower in oseltamivir recipients. Among oseltamivir recipients,
fever occurred most often in the single daily dose group (23%) and least often
in the 200-mg twice daily dose group (7%). Acetaminophen was used by 69% of
placebo and 32% of oseltamivir recipients during the study for symptom relief,
but the majority of subjects took only single doses. The frequency of cough
was low in both groups (<10%).
Among infected placebo recipients, the median nasal lavage levels of
IL-6, TNF-α, and IFN-γ exhibited similar patterns in that peak
responses occurred on day 4 after inoculation in each instance (Figure 5). The magnitude of the median of the IL-6, TNF-α,
and IFN-γ responses were comparable, exhibiting a 4-, 2- and 3-fold
increase above baseline, respectively, on this day. By Spearman rank analysis,
the increases in nasal lavage fluid of IL-6 and IFN-γ levels correlated
significantly (P≤.01) with viral titers on days
3 (coefficients: IL-6, 0.71; IFN-γ, 0.78) and 5 (0.77 and 0.67, respectively)
among placebo recipients. In contrast, oseltamivir treatment significantly
reduced these responses, and no changes were observed in oseltamivir recipients
over the course of the study. The IFN-α response did not show a significant
elevation over the course of the infection, and there was no detectable IL-5
response in either group.
No dose-limiting intolerance was observed, and all subjects completed
the dosing regimen. The overall frequency of adverse events during dosing
did not differ across the groups, but gastrointestinal tract complaints occurred
more often in the oseltamivir recipients (16 [18%] of 88 compared with 2 [7%]
of 29 placebo recipients) during drug administration (95% confidence interval
for difference, −11% to 68%). These were largely manifested as transient
nausea of mild to moderate intensity (15 [17%] of 88 oseltamivir recipients).
Emesis (4 [5%] of 88 oseltamivir recipients) and diarrhea (1 case) were uncommon.
Nausea occurred primarily after the first dose and usually resolved within
1 to 2 days despite continued dosing. In the treatment study, gastrointestinal
tract upset was observed more often in subjects receiving 200-mg doses (9
[28%] of 32 compared with 3 [11%] of 32 receiving lower doses) and in the
fasting state (11 [31%] of 36 compared with 2 [7%] of 28 subjects when administered
with food). No significant changes were seen in clinical laboratory parameters
(data not shown).
Oral administration of the neuraminidase inhibitor oseltamivir provided
significant antiviral, biochemical, and clinical effects in experimental human
influenza virus infection. Prophylactic administration either once or twice
daily completely protected against viral recovery in the upper respiratory
tract and against infection-associated respiratory tract illness. Early treatment
resulted in statistically significant reductions in the magnitude and duration
of viral replication and in the severity and duration of influenza illness.
The magnitude of these effects is comparable with those observed earlier in
studies of intranasal zanamivir tested against the same challenge virus under
similar conditions.2 In addition, the magnitude
of the antiviral effects observed in these studies exceeded those reported
historically with the influenza A–specific inhibitors amantadine and
rimantadine in experimental human influenza.26-31
Both topical zanamivir10,11 and
oral adamantaneamines32-35
have been shown to provide clinical benefits in treating uncomplicated influenza,
and prophylaxis with amantadine or rimantadine also provides substantial protection
against epidemic influenza A illness.36 Such
findings predict that oral oseltamivir should be associated with both prophylactic
and therapeutic activity when studied in natural influenza. Indeed, recently
completed field studies have confirmed the efficacy of oral oseltamivir for
both seasonal prophylaxis 37 and therapy of
acute influenza.38,39
We recently reported that the nasal lavage fluid levels of IL-6 and
TNF-α increase in humans experimentally infected with influenza A virus
and correlate with the clinical and virological features of the illness.24 In this study, we confirm these earlier observations
and also document increases in levels of IFN-γ that parallel the increases
in IL-6 and TNF-α. Among placebo recipients, the increases in levels
of IL-6 and IFN-γ correlated with viral titers. This study verifies
our previous findings of the role of IL-6, TNF-α, and IFN-γ in
the pathogenesis of symptom production in influenza and shows that oral oseltamivir
also reduced these objective markers of host inflammatory responses. These
results further substantiate the links between virus replication, cytokine
elaboration, and symptom production during acute influenza.
Oral oseltamivir was generally well-tolerated in these studies. Both
GS4071 and zanamivir are selective inhibitors of influenza neuraminidase at
low-nanomolar concentrations and show negligible activity against neuraminidases
from human, bacterial, or other viral sources at concentrations up to 1 mmol/L.14,15 In initial human testing, oral oseltamivir
given while fasting was tolerated at single doses up to 1000 mg or repeated
doses up to 500 mg twice daily for 7 days (total of 13 doses).21
The highest doses, particularly repeated doses of 500 mg, were associated
with nausea of mild to moderate intensity. In the current studies, transient
nausea after dosing was observed mainly at the highest (200 mg) dose and was
largely prevented by administering doses with food. The early timing of onset
and the finding that ingestion with food largely prevented this adverse effect
suggest that it might be due to direct gastric irritation, although further
studies of the mechanism are needed. Of note, administration after food is
associated with a modest increase in GS4071 bioavailability.21
These observations suggest that this formulation of oseltamivir should be
administered with food when possible to reduce the risk of gastrointestinal
tract upset.
We did not observe clear dose-related differences in antiviral effects
in the treatment or prophylaxis studies. Although once daily dosing may have
been associated with less pronounced antiviral effects, our sample sizes were
insufficient to make firm conclusions. With respect to prophylaxis, an antiviral
dose that allows for a subclinical but immunizing infection would be optimal.
Under similar conditions, intranasal zanamivir prophylaxis completely protected
against experimental infection in most subjects, so that protective serologic
responses were not observed.2 With oseltamivir
prophylaxis, both once and twice daily administration protected against viral
shedding but allowed some subjects to develop antibodies. Whether lower doses
might be protective against illness but allow immune responses remains to
be determined. Of note, the findings in these studies guided dose selection
for subsequent field trials. The initial results from these studies indicate
that once daily dosing (75 mg) is safe and effective for long-term prophylaxis 37 and twice daily dosing (75 mg) for short-term treatment
of natural influenza in adults.38,39
In summary, the present studies showed oseltamivir to be an effective
antiviral agent when administered orally for prevention and treatment of experimental
influenza A infections. This agent is a promising new drug for the management
of natural influenza.
1.Liu C, Eichelberger MC, Compans RW, Air GM. Influenza type A virus neuraminidase does not play a role in viral
entry, replication, assembly, or budding.
J Virol.1995;69:1099-1106.Google Scholar 2.Hayden FG, Treanor JJ, Betts RF, Lobo M, Esinhart JD, Hussey EK. Safety and efficacy of the neuraminidase inhibitor GG167 in experimental
human influenza.
JAMA.1996;275:295-299.Google Scholar 3.Burnet FM. Mucins and mucoids in relation to influenza virus action, III: inhibition
of virus haemagglutination by glandular mucins.
Aust J Exp Biol Med Sci.1948;26:371-379.Google Scholar 4.Colman PM, Varghese JN, Laver WG. Structure of the catalytic and antigenic sites in influenza virus neuraminidase.
Nature.1983;303:41-44.Google Scholar 5.Colman PM. Influenza virus neuraminidase: structure, antibodies, and inhibitors.
Protein Sci.1994;3:1687-1696.Google Scholar 6.Varghese JN, McKimm-Breschkin JL, Caldwell JB, Kortt AA, Colman PM. The structure of the complex between influenza virus neuraminidase
and sialic acid, the viral receptor.
Proteins.1992;14:327-332.Google Scholar 7.von Itzstein M, Wu WY, Kok GB.
et al. Rational design of potent sialidase-based inhibitors of influenza virus
replication.
Nature.1993;363:418-423.Google Scholar 8.Ryan DM, Ticehurst J, Dempsey MH, Penn CR. Inhibition of influenza virus replication in mice by GG167 (4-guanidino-2,4-dideoxy-2,3-dehydro-N-acetylneuraminic
acid) is consistent with extracellular activity of viral neuraminidase (sialidase).
Antimicrob Agents Chemother.1994;38:2270-2275.Google Scholar 9.Ryan DM, Ticehurst J, Dempsey MH. GG167 (4-guanidino-2,4-dideoxy-2,3-dehydro-N-acetylneuraminic acid)
is a potent inhibitor of influenza virus in ferrets.
Antimicrob Agents Chemother.1995;39:2583-2584.Google Scholar 10.Hayden FG, Osterhaus ADME, Treanor JJ.
et al. Efficacy and safety of the neuraminidase inhibitor zanamivir in the
treatment of influenza virus infections.
N Engl J Med.1997;337:874-879.Google Scholar 11.MIST Study Group. Randomized trial of efficacy and safety of inhaled zanamivir in treatment
of influenza A and B virus infections.
Lancet.1998;352:1877-1881.Google Scholar 12.Cass LMR, Efthymiopoubs C, Bye A. Pharmacokinetics of zanomivir after intravenous, oral inhaled, or intranasal
administration to healthy volunteers.
Clin Pharmacokinet.1999;36(suppl):1-11.Google Scholar 13.Cass LMR, Brown J, Pickford M.
et al. Pharmacoscintigraphic evaluation of lung deposition of inhaled zanomivir
in healthy volunteers.
Clin Pharmacokinet.1999;36(suppl):21-31.Google Scholar 14.Kim CU, Lew W, Williams MA.
et al. Influenza neuraminidase inhibitors possessing a novel hydrophobic interaction
in the enzyme active site: design, synthesis, and structural analysis of carbocyclic
sialic acid analogues with potent anti-influenza activity.
J Am Chem Soc.1997;119:681-690.Google Scholar 15.Mendel DB, Tai CY, Escarpe PA.
et al. Oral administration of a prodrug of the influenza virus neuraminidase
inhibitor GS4071 protects mice and ferrets against influenza infection.
Antimicrob Agents Chemother.1998;42:640-646.Google Scholar 16.Hayden FG, Rollins BS. In vitro activity of the neuraminidase inhibitor GS4071 against influenza
viruses.
Antiviral Res.1997;34:A86.Google Scholar 17.Li W, Escarpe PA, Eisenberg EJ.
et al. Identification of GS4104 as an orally bioavailable prodrug of the influenza
virus neuraminidase inhibitor GS4071.
Antimicrob Agents Chemother.1998;42:647-653.Google Scholar 18.Sidwell RW, Huffman JH, Barnard DL.
et al. Inhibition of influenza virus infections in mice by GS4104, an orally
effective influenza virus neuraminidase inhibitor.
Antiviral Res.1998;37:107-120.Google Scholar 19.Kim CU, Bischofberger N, Williams MA, Lew W, Merson J, Sweet C. Efficacy of GS4104 in ferrets infected with influenza A virus.
Antiviral Res.1997;34:A74.Google Scholar 20.Eisenberg G, Bidgood A, Lynch G, Lee WA, Cundy K. Penetration of GS4071: a novel influenza neuraminidase inhibitor into
rat bronchoalveolar lining fluid following oral administration of the prodrug
GS4104.
Antimicrob Agents Chemother.1997;41:1949-1952.Google Scholar 21.Wood ND, Aitken M, Sharp S, Evison H. Tolerability and pharmacokinetics of the influenza neuraminidase inhibitor
Ro-64-0802 (GS4071) following oral administration of the prodrug Ro-64-0796
(GS4104) to healthy male volunteers. In: Abstracts of the 37th Interscience Conference on Antimicrobial
Agents and Chemotherapy; September 28-October 1, 1997; Toronto, Ontario. Abstract
A-123.
22.Hayden FG, Tunkel AR, Treanor JJ, Betts RF, Allerheiligen S, Harris J. Oral LY217896 for prevention of experimental influenza A virus infection
and illness in humans.
Antimicrob Agents Chemother.1994;38:1178-1181.Google Scholar 23.Walker JB, Hussey EK, Treanor JJ, Montalvo A, Hayden FG. Effects of the neuraminidase inhibitor zanamivir on otologic manifestations
of experimental human influenza.
J Infect Dis.1997;176:1417-1422.Google Scholar 24.Hayden FG, Fritz RS, Lobo M, Alvord G, Strober W, Straus SE. Local and systemic cytokine responses during experimental human influenza
A virus infection.
J Clin Invest.1998;101:643-649.Google Scholar 25.Santer TJ, Snell MK. Small-sample confidence intervals for P
1-P
2 and
P
1/P
2 in 2×2 contingency tables.
J Am Stat Assoc.1980;75:386-394.Google Scholar 26.Sears SD, Clements ML. Protective efficacy of low-dose amantadine in adults challenged with
wild-type influenza A virus.
Antimicrob Agents Chemother.1987;31:1470-1473.Google Scholar 27.Smorodintsev AA, Zlydnikov DM, Kiseleva AM, Romanov JA, Kazantsev AP, Rumovsky VI. Evaluation of amantadine in artificially induced A2 and B influenza.
JAMA.1970;213:1448-1454.Google Scholar 28.Reuman PD, Bernstein DI, Keefer MC, Young EC, Sherwood JR, Schiff GM. Efficacy and safety of low dosage amantadine hydrochloride as prophylaxis
for influenza A.
Antiviral Res.1989;11:27-40.Google Scholar 29.Jackson GG, Muldoon RL, Akers LW. Serological evidence for prevention of influenzal infection in volunteers
by an anti-influenzal drug adamantanamine hydrochloride.
Antimicrob Agents Chemother.1963;3:703-707.Google Scholar 30.Dawkins ATJ, Gallager LR, Togo Y, Hornick RB, Harris BA. Studies on induced influenza in man, II: double-blind study designed
to assess the prophylactic efficacy of an analogue of amantadine hydrochloride.
JAMA.1968;203:1095-1099.Google Scholar 31.Hayden FG, Zlydnikov DM, Iljenko VI, Padolka YV. Comparative therapeutic effect of aerosolized and oral rimantadine
HCl in experimental human influenza A virus infection.
Antiviral Res.1982;2:147-153.Google Scholar 32.Hayden FG, Monto AS. Oral rimantadine hydrochloride therapy of influenza A virus H3N2 subtype
infection in adults.
Antimicrob Agents Chemother.1986;29:339-341.Google Scholar 33.Hayden FG, Sperber SJ, Belshe RB, Clover RD, Hay AJ, Pyke S. Recovery of drug-resistant influenza A virus during therapeutic use
of rimantadine.
Antimicrob Agents Chemother.1991;35:1741-1747.Google Scholar 34.Togo Y, Hornick RB, Felitti VJ.
et al. Evaluation of therapeutic efficacy of amantadine in patients with naturally
occurring A2 influenza.
JAMA.1970;211:1149-1156.Google Scholar 35.VanVoris LP, Betts RF, Hayden FG, Christmas WA, Douglas RGJ. Successful treatment of naturally occurring influenza A/USSR/77 H1N1.
JAMA.1981;245:1128-1131.Google Scholar 36.Douglas RGJ. Prophylaxis and treatment of influenza.
N Engl J Med.1990;322:443-450.Google Scholar 37.Hayden FG, Atmar RL, Schilling M.
et al. Safety and efficacy of oral GS4104 in long-term prophylaxis of natural
influenza. In: Final Program, Abstracts and Exhibits Addendum: 38th Annual Interscience
Conference on Antimicrobial Agents and Chemotherapy; September 24-27, 1998;
San Diego, Calif. Abstract LB-6.
38.Treanor JJ, Vrooman PS, Hayden FG, Kinnersley N, Ward P, Mills RG. Efficacy of oral GS4104 in treating acute influenza. In: Final Program, Abstracts and Exhibits Addendum: 38th Annual Interscience
Conference on Antimicrobial Agents and Chemotherapy; September 24-27, 1998;
San Diego, Calif. Abstract LB-4.
39.Aoki FY, Osterhaus AD, Rimmelzwaan GF, Kinnersley N, Ward P. Oral GS4104 successfully reduces duration and severity of naturally
acquired influenza. In: Final Program, Abstracts and Exhibits Addendum: 38th Annual Interscience
Conference on Antimicrobial Agents and Chemotherapy; September 24-27, 1998;
San Diego, Calif. Abstract LB-5.