Successful treatment of naturally occurring influenza A/USSR/77 H1N1. Comparison of amantadine and rimantadine for prevention of type A (Russian) influenza. A controlled trial of amantadine and rimantadine in the prophylaxis of influenza A infection. Comparative toxicity of amantadine hydrochloride and rimantadine hydrochloride in healthy adults. Evaluation of amantadine hydrochloride in the treatment of A2 influenzal disease. Administration of amantadine for the prevention of Hong Kong influenza. Amantadine therapy of epidemic influenza a(2) (Hong Kong). Reduction in fever and symptoms in young adults with influenza A/Brazil/78 H1N1 infection after treatment with aspirin or amantadine. Safety and prophylactic efficacy of low-dose rimantadine in adults during an influenza A epidemic. Evaluation of amantadine in the prophylaxis of influenza A (H1N1) virus infection: a controlled field trial among young adults and high-risk patients. Inhaled zanamivir versus rimantadine for the control of influenza in a highly vaccinated long-term care population. The prophylactic effectiveness of amantadine hydrochloride in an epidemic of Hong Kong influenza in Leningrad in 1969. Efficacy and safety of low dosage amantadine hydrochloride as prophylaxis for influenza A. Effectiveness of rimantadine prophylaxis of children within families. Children with influenza A infection: treatment with rimantadine. Prevention of Russian influenza by amantadine. Therapeutic efficacy of amantadine HCl and rimantadine HCl in naturally occurring influenza A2 respiratory illness in man. Therapeutic effects of aerosolized amantadine in naturally acquired infection due to influenza A virus. Safety and efficacy of long-term use of rimantadine for prophylaxis of type A influenza in nursing homes. Rimantadine prophylaxis in children: a follow-up study. Oral rimantadine hydrochloride therapy of influenza A virus H3N2 subtype infection in adults. Protection of man from natural infection with influenza A2 Hong Kong virus by amantadine: a controlled field trial. [Therapeutic efficacy of amantadine hydrochloride in patients with epidemic influenza A virus infection]. Effect of rimantadine on the immune response to influenza A infections. Use and withdrawal of amantadine chemoprophylaxis during epidemic influenza A. The roles of vaccination and amantadine prophylaxis in controlling an outbreak of influenza A (H3N2) in a nursing home. Influenza A prophylaxis with amantadine in a boarding school. Safety of prolonged administration of rimantadine hydrochloride in the prophylaxis of influenza A virus infections in nursing homes. Therapeutic effectiveness of amantadine hydrochloride in influenza A2--double blind studies. Therapeutic effectiveness of amantadine hydrochloride in naturally occurring Hong Kong influenza--double-blind studies. Treatment of influenza. The therapeutic efficacy of rimantadine HC1 in a naturally occurring influenza A2 outbreak.
Forty-five university students with proved influenza A/USSR/77 H1N1 infection were randomly treated with either amantadine hydrochloride (14 students), rimantadine hydrochloride (19 students), or placebo (12 students). By 48 hours after initiation of therapy, amantadine and rimantadine recipients had significantly less fever and greater improvement compared with subjects given the placebo. Minor reversible CNS side effects at the end of the five-day course of therapy were observed in one third of the amantadine-treated subjects. However, both amantadine and rimantadine recipients returned to classes earlier and shed smaller amounts of virus than placebo recipients. Thus, both drugs exerted a notable therapeutic effect. Hence, during an influenza outbreak, five days of empirical therapy with amantadine or rimantadine for persons with an influenza-like syndrome should ameliorate clinical symptoms and might decrease spread of virus. The efficacies of 200 mg of daily doses of amantadine and of rimantadine for prevention of infection and illness due to influenza A/USSR/77 (H1N1) virus were compared in a double-blind, placebo-controlled study on a college campus. Frequencies of symptoms that might have been side effects of the drugs were not significantly different from those in placebo recipients. Analyses indicated that the trial was initiated late in the epidemic and that an age-related protective effect against A/USSR virus existed; seroconversion frequencies were 52/139 (37%) among 18-19-year-olds, 33/130 (25%) among 20-21-year-olds, and 5/39 (12.8%) among 22-24-year-olds. Among initially antibody-negative (less than 1 : 4 in complement fixing and neutralizing tests and less than 1 : 8 in hemagglutination inhibition tests) 18-19-year-old students, amantadine was associated with significantly fewer seroconversions (P = 0.01) and both less infection and milder illness than occurred in placebo recipients (P less than 0.05). Although rimantadine was not accompanied by reduction in frequency of seroconversions in the same age group, illness frequency and severity among seroconverters were significantly reduced when compared to placebo recipients (P less than 0.01). Amantadine and rimantadine appear suitable for use in young adults. Although other studies have suggested greater effectiveness of rimantadine than of amantadine against influenza, no evidence for this was seen in the present study which used both drugs at the same dose. Four hundred fifty volunteers participated in a placebo-controlled, double-blind, randomized trial of the prophylactic effects of rimantadine and amantadine during an outbreak of influenza A. The subjects received drugs orally at a dose of 100 mg twice a day for six weeks. Influenza-like illness occurred in 41 per cent of the subjects receiving placebo but in only 14 per cent of those receiving rimantadine and 9 per cent of these receiving amantadine (P less than 0.001 for either drug vs. placebo). Laboratory-documented influenza occurred in 21 per cent of placebo recipients, 3 per cent of rimantadine recipients, and 2 per cent of amantadine recipients (P less than 0.001). These findings represent efficacy rates of 85 per cent for rimantadine and 91 per cent for amantadine, as compared with placebo. More recipients of amantadine (13 per cent) than recipients of rimantadine (6 per cent; P less than 0.05) or placebo (4 per cent; P less than 0.01) withdrew from the study because of central-nervous-system side effects. On the basis of this study, rimantadine appears to be the drug of choice for the prophylaxis of influenza A. The relative toxicities of amantadine and rimantadine were compared in a double-blind, placebo-controlled study involving healthy adults. In separate studies, drugs were administered at a dosage of 200 mg/day (52 volunteers) or 300 mg/day (196 volunteers) for 4.5 days. Both drugs were well tolerated at the lower dosage. At 300 mg/day amantadine recipients had a greater frequency and severity of central nervous system (nervousness, lightheadedness, difficulty concentrating) and sleep (insomnia, fatigue) complaints compared with rimantadine or placebo recipients. Amantadine recipients also performed less well on an objective test measuring sustained attention and problem-solving ability. Both amantadine and rimantadine recipients reported adverse gastrointestinal symptoms more often than placebo recipients. Because of better tolerance at higher dosage, rimantadine offers more promise than amantadine for treatment of influenza A virus infections. Amantadine hydrochloride is the first drug to show promise as a practical anti-influenza agent. Several studies demonstrating a prophylactic effect in volunteers with induced A2 disease as well as in patients during A2 outbreaks have created the impetus for therapeutic trials. The widespread A2 influenza epidemic that occurred early in 1968 provided the opportunity for therapeutic evaluation in the USA.A total of 197 prison inmates with proven influenza agreed to participate in the 10-day double-blind evaluation of amantadine (100 mg, twice daily). Onset of therapy was approximately 20 hours after first subjective awareness of illness.Assessment of drug effectiveness was based on rapidity of resolution of illness. There was a significant increase in the number of drug-treated as against placebo patients in the "rapid resolver" group whereas individuals receiving placebo dominated the "slow resolver" group. Analysis of febrile responses indicated that amantadine-treated patients had significantly more rapid defervescence. Virus isolation studies revealed etiologically related virus in 90% of all volunteers during the first 5 days of therapy. It was apparent that clinical improvement was not correlated with disappearance of the virus. Nevertheless, the trials conducted during the influenza season of early 1968 indicated the therapeutic effect of amantadine hydrochloride. Administration of 100 mg, twice daily, for 10 days did not cause any adverse effects. The prophylactic effectiveness of amantadine against A2/Hong Kong influenza was investigated in the course of a double-blind trial in Braşov, Romania, during an epidemic due to the Hong Kong virus that started there in March 1969.Altogether 215 subjects were included in the trial; 112 received 100 mg of amantadine twice daily for 20 days and the remaining 103 received inert placebo tablets. Of the amantadine-treated group, 2 had clinical symptoms diagnosed as influenza (1 of these was a doubtful diagnosis), whereas 20 (1 doubtful) of the placebo group had such symptoms. No case with both clinical symptoms and serologically confirmed influenza (>/=4-fold increase in haemagglutination-inhibition titre) occurred among 77 amantadine-treated subjects for whom paired sera were available but there were 13 such cases among the 74 placebo subjects with paired sera. These differences are statistically highly significant. No serious side-effects were recorded.The authors conclude that amantadine was highly effective in preventing overt disease and discuss indications that suggest that it did not interfere with the development of immunity in persons treated during the incubation period. In a double-blind comparison of the therapeutic effect of amantadine in a natural outbreak of Hong Kong influenza in January 1969 near Houston, Texas, the decrease in titers of virus in throat swabs from 12 treated patients during the first 10 hr of treatment was appreciably greater than similar titers of virus from 16 untreated patients (P = 0.06). The titer of shed virus decreased significantly more rapidly (P < 0.05) among amantadine-treated patients ill more than 48 hr before treatment than among five control patients who had been ill more than 48 hr. Cough, sore throat, and nasal obstruction cleared more rapidly in treated patients (P < 0.05), and decline of fever in 6 treated patients sick for less than 48 hr before treatment was more rapid than among 13 untreated patients who had been ill for less than 48 hr. These findings are considered to be consistent with a limited therapeutic effect of the drug. During an outbreak of influenza A/Brazil/78 H1N1 infection, 47 volunteers with clinical and virological influenza of less than 2 days duration were treated in a randomized double-blind fashion for 5 days with 100 or 200 mg of amantadine daily or with 3.25 g of aspirin daily. The aspirin treatment group defervesced more rapidly (10.3 h versus 21.5 h and 23.6 h; P less than 0.01), but by the second daily follow-up visit, both groups of amantadine recipients exhibited greater symptomatic improvement. Bothersome side effects resulted in discontinuation of therapy by 35% of the aspirin treatment group but only 3% of the amantadine treatment group (P less than 0.05). Individuals who present to a physician during an influenza A epidemic with characteristic symptoms will experience symptomatic benefit from amantadine treatment, with negligible toxicity. A placebo-controlled, double-blind study to evaluate the safety and prophylactic efficacy of a low dose (100 mg) of rimantadine hydrochloride against naturally occurring influenza in adults was conducted at two sites. After the onset of the influenza season, volunteers (ages, 18 to 55 years) were assigned randomly to receive rimantadine or placebo daily. Subjects were monitored for adverse effects and evidence of influenza virus infection weekly for six weeks. Only 10 (8.7%) of 114 rimantadine recipients and 5 (4.4%) of 114 placebo control recipients reported one or more mild to moderate adverse symptoms, most of which were related to the gastrointestinal or central nervous system. Compared with placebo, low-dose rimantadine was highly effective in the prevention of influenza A virus infection (20 of 110 versus 7 of 112 participants; P less than 0.01) and influenza illness (7 of 110 versus 1 of 112 participants; P = 0.04). Influenza A/Leningrad/87-like (H3N2) virus was recovered from the nasopharynxes of only five placebo recipients. These findings indicate that low-dose rimantadine is well tolerated and highly effective for the prevention of influenza A illness in healthy adults. The usefulness of amantadine in the protection of humans against influenza A (H1N1) virus was evaluated in a double-blind field trial with 555 volunteers in Finland in the winter of 1978. Three populations--patients in a general hospital, adults in a home for the aged, and two groups of military conscripts--were chosen. Epidemic influenza occurred only in the two groups of conscripts: the incidence of serologically verified influenza was 66% and 83% in the groups that received placebo and 43% and 51% in the groups that received amantadine, giving protection rates of 36% (P = 0.05) and 39% (P = 0.001). The evaluation of the effect of amantadine on the occurrence of illness was obscured by concomitant adenoviral infections that caused influenza-like symptoms. No clear difference in the occurrences of side effects was observed between the placebo and amantadine-treated groups; however, a significantly greater number of participants who took 200 mg of amantadine/day (16.9%) stopped medication during the trial as compared with the placebo groups (7.6%) (P < 0.02). Despite vaccination, influenza commonly causes morbidity and mortality in institutional settings. Influenza control with rimantadine and amantadine is limited by emergence and transmission of drug-resistant influenza A variants, ineffectiveness against influenza B, and toxicity. This study evaluated the efficacy and tolerability of zanamivir versus rimantadine for influenza outbreak control in long-term care facilities.
                This double-blind, randomized, controlled study prospectively enrolled nursing home residents for 3 influenza seasons (1997 to 2000). Vaccine was offered to all subjects. Following influenza outbreak declaration, subjects were randomized to inhaled zanamivir 10 mg or standard of care (rimantadine 100 mg for influenza A or placebo for influenza B) once daily for 14 days. The proportion of randomized subjects developing symptomatic, laboratory-confirmed influenza during prophylaxis was the primary endpoint.
                Of 482 randomizations (238 zanamivir, 231 rimantadine, 13 placebo), 96% of subjects were elderly or had high-risk conditions; over 90% were vaccinated. Symptomatic, laboratory-confirmed influenza occurred in 3% of zanamivir subjects and 8% of rimantadine subjects during chemoprophylaxis (P = .038; additional protective efficacy for zanamivir over rimantadine = 61%). Since only 25 subjects were randomized during 2 influenza B outbreaks and none developed influenza, the influenza B data were excluded from further analysis. Zanamivir was well tolerated and unassociated with emergence of resistant virus; rimantadine-resistant variants were common.
                This is the first prospective, controlled study demonstrating effectiveness of chemoprophylaxis for influenza outbreak control. Zanamivir prevents symptomatic, laboratory-confirmed influenza more effectively than rimantadine, is unassociated with resistant virus, and has a favorable safety profile. Zanamivir is an appropriate alternative for influenza outbreak control among institutionalized vaccinated elderly. The effectiveness of amantadine hydrochloride as a prophylactic against influenza was studied during an epidemic caused by viruses related to influenza A2/Hong Kong/1968 variants in Leningrad, USSR, early in 1969. In all, 8169 subjects, assigned to amantadine-dosed, placebo-dosed, internal control and external control groups, were assessed. The index of effectiveness of the prophylactic medication, based on clinical diagnosis, in subjects who took amantadine regularly was 1.95. When the clinical diagnoses were confirmed serologically the index of effectiveness for the amantadine compared with the placebo group increased to 2.7. A comparison of the medicated group with the non-medicated, non-isolated internal control group showed an index of effectiveness of 5.34. A daily dose of 100 mg of amantadine was associated with an increase of 1.14% in complaints of sleep disturbances but these had no effect on the working capacity of subjects. The efficacy and safety of prophylactic low dose amantadine hydrochloride was assessed in two double-blind, placebo-controlled, randomized studies. In a study of 476 subjects aged 18 to 55 years, adverse reactions were not significantly different between the group receiving 100 mg/day amantadine and the placebo group but significantly greater in the group given 200 mg/day (P less than 0.009). The influenza attack rate in this study was too low to assess efficacy. In an experimental challenge study of influenza A/Beth/1/85 in 78 subjects of similar age the prophylactic administration of 50 mg, 100 mg or 200 mg/day doses of amantadine were more effective than placebo in preventing influenza illness (P less than 0.02, 66, 74 and 82% protection, respectively), and in suppressing viral replication (P = 0.02). There was no significant difference between amantadine groups in influenza illness or viral shedding. Compared with the placebo group the 100 and 200 mg amantadine groups showed a significant decrease in infection rate (100 mg: 40% protection: P = 0.012; 200 mg: 32% protection: P = 0.045) whereas the 50 mg group did not (20% protection: P = 0.187). These results suggest that 100 mg/day of amantadine will reduce toxicity but maintain the prophylactic efficacy seen with 200 mg/day. With recent studies suggesting that children are the main introducers of influenza infections into families, we conducted a placebo-controlled, double-blind, randomized trial to study the prophylactic effectiveness of rimantadine hydrochloride in children on the transmission of influenza A infections within families. One hundred forty-five volunteers from 35 families completed this study during a naturally occurring outbreak of influenza A (H1N1) infection. Influenza infections, defined as a positive viral throat culture or a fourfold increase in antibody titer, occurred in 31.7% of children in the placebo group and 2.9% of children in the rimantadine group. Clinical illness with laboratory evidence of influenza infection occurred in 17.0% of children in the placebo group and 0% of children in the rimantadine group. Rimantadine was well tolerated by the children, with no significant difference in reported side effects between the placebo and rimantadine groups. Influenza A infection occurred in 19.0% of adults whose children were receiving a placebo and 8.8% of adults whose children were receiving rimantadine. On the basis of our study, rimantadine prophylaxis of children appears to be an effective method to prevent influenza A infection in children. Additional studies are needed to demonstrate the effects of rimantadine prophylaxis of children on the incidence of influenza A infection in their parents. Treatment with rimantadine of influenza in children and the potential development of resistance in clinical isolates associated with therapy have not been previously studied. We compared rimantadine to acetaminophen therapy in a controlled, double-blind study of 91 children with influenza-like illness. Of 69 children with proven influenza A/H3N2 infection, 37 received rimantadine and 32 received acetaminophen for five days. Children receiving rimantadine showed significantly greater reduction in fever and improvement in daily scores for symptoms and severity of illness during the first three days. Viral shedding also diminished significantly during the first two days but subsequently increased such that by days 6 and 7 the proportion of children shedding virus, as well as the quantity of virus shed, was significantly greater in the rimantadine group. During the seven-day study, of the 22 children in the rimantadine group with serial isolates tested, ten (45.5%) had resistant isolates compared with two (12.5%) of those with serial isolates in the acetaminophen group (P less than .03). Thus, of the total 37 children in the rimantadine group, 27% were found to have resistant isolated compared with 6% in the total group receiving acetaminophen (P less than .04). Furthermore, the mean inhibitory concentration of rimantadine increased with time in the rimantadine group (r = .4, P = .002) but not in the acetaminophen group. Rimantadine therapy, thus, appears to be significantly more effective than acetaminophen in ameliorating the clinical signs and symptoms of influenza in children. Treatment with rimantadine was also associated with increased viral shedding after the medication was discontinued and with the development of resistance in the clinical isolates, the significance of which is unknown. We tested the effectiveness of amantadine hydrochloride in prevention of illness and infection caused by Russian (h1n1) influenza. The trial lasted seven weeks and was double-blind and placebo controlled. The dosage used was 200 mg daily. Efficacy in prevention of serologically confirmed clinical influenza was 70.7%. Efficacy in prevention of infection, symptomatic or asymptomatic, was 39.4%. Side effects seen were all mild, began within two days of the start of the trial, and terminated rapidly on cessation of prophylaxis. The withdrawal rate attributable to use of amantadine was 6.2%. Those who continued to receive prophylaxis for the remainder of the trial did not exhibit excess side effects. It is concluded that amantadine is safe and effective in prophylaxis of H1N1 strains, as has been shown previously for other subtypes of A influenza. nan The effect of small-particle aerosol therapy with amantadine was assessed in a randomized, double-blind study of 20 patients with naturally acquired influenza A virus infection. Aerosol treatments of 20 min with either distilled water or with amantadine hydrochloride (1.0 g/100 ml of distilled water) were given three times a day for four days. The amantadine-treated patients experienced a significantly more rapid resolution of clinical signs and symptoms when compared with placebo-treated patients. The resolution of fever was similar for both groups. Aerosol delivery of amantadine did not affect the frequency of viral isolation from upper respiratory tract secretions but was associated with a trend toward reduced quantity of viral shedding. Serial pulmonary function tests found no important differences between the groups. Amantadine-treated patients experienced a greater frequency of mild local side effects (rhinorrhea, nasal irritation) during aerosol exposures, but aerosol treatments did not cause any apparent decline in pulmonary function. The safety and efficacy of rimantadine for long-term prophylaxis of influenza A (H3N2) infection were evaluated among elderly residents in 10 nursing homes. Within each nursing home, participating residents were randomly assigned to receive placebo or rimantadine at 100 or 200 mg/day. Residents were evaluated daily for symptoms and significant health events as possible side effects, as well as for influenza-like illness. The study medications were administered to 328 residents for up to 8 weeks, with no statistically significant differences in the frequencies of gastrointestinal or central nervous system symptoms between the groups. However, residents in the active medication groups were more likely to withdraw from the study and to experience various health events including death; some but not all of these differences were statistically significant. Efficacy evaluations were carried out on the 68 vaccinated residents in the two nursing homes with demonstrated influenza virus activity. Rimantadine appeared to provide an additional protective effect beyond vaccination in reducing the risk of clinical and laboratory-confirmed influenza-like illness; however, the efficacy estimates were never statistically significant. The efficacies of the 100- and 200-mg/day dosages were generally similar. When data for the 100- and 200-mg/day dosage groups were combined and compared with data for the group receiving placebo, the efficacy of rimantadine in reducing the risk of clinical influenza-like illness was estimated to be 58 percent (P = 0.079). The results suggest the relative safety and clinical efficacy of using rimantadine for influenza prophylaxis among vaccinated elderly individuals and support the recommendation for a dosage reduction to 100 mg/day in this population. In a randomized, double-blind placebo-controlled clinical trial, we evaluated the prophylactic effectiveness of rimantadine in children (ages 1 to 18 years) against infection with influenza A (H3N2) and associated illness and the prevention of transmission of infection to adult members of the child's family. One hundred ten volunteers from 29 families completed this study during a naturally occurring outbreak of influenza A (H3N2). Influenza infections, defined as a positive viral throat culture or a 4-fold increase in antibody titer, occurred in 31.0% of children in the placebo group and 7.4% in the rimantadine group (P = 0.026). Clinical illness with laboratory evidence of influenza infection occurred in 24.1% of children in the placebo group and none in the rimantadine group (P = 0.007). Rimantadine was well-tolerated by the children, with no significant difference in reported adverse effects between the placebo and rimantadine groups. A combined analysis by families of these data and those of our similarly designed 1984 study, revealed that families in whom the children were given rimantadine had a significantly lower rate of influenza A infection and influenza-like illness compared with the families in whom the children were given placebo (68.8% vs. 18.8%, P less than 0.001) and (56.3% vs. 12.5%, P less than 0.001), respectively. We conclude that rimantadine prophylaxis of children appears to be an effective method to prevent influenza A (either H1N1 or H3N2) infection and illness in children. In a randomized, double-blind trial involving patients with uncomplicated influenza A H3N2 subtype virus infection, rimantadine treatment (200 mg/day for 5 days) was associated with significant reductions in nasal secretion viral titers (days 2 through 4), maximal temperature (days 2 and 3), time until defervescence (mean, 37 h shorter), and systemic symptoms compared with placebo treatment. Prophylactic administration of amantadine in doses of 100 mg. twice a day offered statistically significant protection against influenza A2 infection in a double-blind field trial involving 391 medical student volunteers during the influenza A2 Hong Kong epidemic in Helsinki in the winter of 1969. Serologically verified influenza, as measured by complement fixation and/or haemagglutination inhibition, occurred in 27 out of 192 students in the amantadine group against 57 out of 199 in the placebo group, giving a protection rate of 52%. A virus infection was studied using half of the normal oral dose of amantadine hydrochloride-100 mg/d instead of 200 mg/d. The patients in this study, who visited the clinics during January and February 1999, were confirmed within 48 hours to have influenza A virus infections by the Directigen FluA test. Using a quasi-randomized controlled trial, 26 patients were treated with amantadine hydrochloride in addition to the usual medication, while 23 were treated with only the ordinary medication. There were no significant differences in the mean age, 35.6 years old, or in clinical features between the two groups. The period of fever over 38 degrees C in the amantadine treated group was 1 day while that in the control group was 1.7 days, which shows a significant difference (p = 0.049). There was no significant difference in the duration of aching, such as arthralgia, or of general fatigue. There was no significant difference in the appearance of subsequent new symptoms after the onset of influenza A virus infection. In conclusion, it is expected that oral amantadine hydrochloride, 100 mg/d, together with the ordinary medication, will reduce the duration of the period of fever over 38 degrees C. The effects of rimantadine on lymphocyte responses to mitogens CON-A and PHA, natural killer cell activity, and the development of serum and local antibodies were studied during an epidemic outbreak of influenza A (H3N2). Twenty-three families consisting of 38 adults and 46 children had a member who developed a flu-like illness and were randomly assigned to receive placebo or rimantadine either as treatment or post exposure prophylaxis. Nasal washings for virus isolation and IgG and IgA determination were collected on days 1, 5, and 10 of illness. Blood samples for immunologic studies were obtained on days 1 and 5 of clinical illness and on day 21. No differences in lymphocyte responses to CON-A and PHA or in natural-killer cell activity were noted between placebo and rimantadine groups. The development of neutralizing antibodies to influenza H3N2 was also not affected by rimantadine. However, the presence of IgA in nasal secretions was significantly diminished in the rimantadine group compared to the placebo group (0/9 vs. 6/9, P less than 0.005). The findings indicate that rimantadine had no adverse affect on the systemic immune system. However, local immune response was diminished in individuals taking rimantadine possibly due to the presence of less immunogen resulting from reduction of virus in secretions of individuals taking antivirals. A controlled investigation of chemoprophylaxis with amantadine hydrochloride during an epidemic of influenza A was performed in nonimmune students. Illness was significantly decreased and serologic evidence of infection reduced by treatment. During the post-treatment period, while influenza was still prevalent, an accelerated rate of infection occurred among persons previously protected by chemotherapy. When used, chemoprophylaxis should be continued until influenza is no longer prevalent or, preferably, should be combined with vaccine administration to ensure protection after treatment. An outbreak caused by influenza A/Philippines/2/82 (H3N2)-like viruses occurred in a partially vaccinated nursing home population in January 1985. During the first six days of the outbreak, 14 (25%) of 55 residents developed influenzalike illness. The risk of illness was most strongly associated with undetectable levels of antibody against the epidemic strain, with unvaccinated case-patients having more severe illnesses and a higher rate of hospitalization than vaccinated case-patients (5/8 vs 0/6). During the period of amantadine hydrochloride prophylaxis (100 mg/d) from days 7 to 35, only two (5%) of the remaining 41 residents became ill, even though 11 (27%) had no detectable antibody. Serum amantadine levels obtained on day 35 ranged from 117 to 737 ng/mL (mean 309 ng/mL), similar to therapeutic levels documented in younger adults who have taken the standard regimen of 200 mg/d; there were few clinically significant side effects. These findings illustrate the benefits of influenza vaccination and support the use of amantadine hydrochloride at a dosage of 100 mg daily for outbreak control among elderly persons. In a boarding school for boys, where routine influenza vaccination is carried out annually, 267 boys were given amantadine (100 mg daily) and 269 received no specific treatment during an influenza A (H1N1) outbreak. 3 boys receiving amantadine and 29 boys receiving no medication had laboratory-proven influenza A. There are circumstances when the prophylactic use of amantadine may be justified for the control of influenza A outbreaks in boarding schools and other institutions where high attack-rates are experienced. We evaluated the safety of rimantadine hydrochloride (RH) prophylaxis in a double-blind, placebo-controlled trial in three nursing homes during a community epidemic of influenza A (H3N2). Although daily monitoring of the 35 participants revealed an association between RH administration (100 mg twice a day) and the development of nausea and anxiety (P less than 0.05), these and other potential side effects were transient and were rarely considered to be clinically significant. Serum RH levels measured at the end of the trial (mean, 1,159 ng/ml) were nearly three times higher than those measured previously in younger individuals, suggesting that lower dosages may be indicated for the elderly. nan nan nan
Amantadine and rimantadine have comparable efficacy and effectiveness in relieving or treating symptoms of influenza A in healthy adults, although rimantadine induces fewer adverse effects than amantadine. The effectiveness of both drugs in interrupting transmission is probably low. Resistance of influenza viruses to amantadine is a serious worldwide problem as shown by recent virological surveillances. Both drugs have adverse gastrointestinal (stomach and gut) effects, but amantadine can also have serious effects on the nervous system. They should only be used in an emergency when all other measures fail.