Adverse reactions to amantadine prophylaxis of influenza in a retirement home

Prevention of Nosocomial Influenza

Objective:

To study compliance with preventive strategies at a university hospital during an outbreak of nosocomial influenza A during the winter of 1988, and the rates of vaccination of healthcare workers and of nosocomial influenza following changes in vaccine practices after the outbreak.

Design:

Retrospective review of employee health, hospital epidemiology, hospital computing, and clinical microbiology records.

Setting:

A university hospital.

Interventions:

Unvaccinated personnel with exposure within the previous 72 hours to an unisolated case of influenza were offered influenza vaccine and 14 days of amantadine hydrochloride prophylaxis. Personnel with exposure more than 72 hours before evaluation were offered vaccine. A mobile cart was introduced for vaccinating personnel after the 1988 outbreak.

Results:

An outbreak of influenza with 10 nosocomial cases occurred in 1988. Only 4% of exposed employees had been vaccinated previously and 23% of exposed, unvaccinated employees agreed to take vaccine, amantadine, or both. A mobile-cart vaccination program was instituted, and annual vaccination rates steadily increased from 26.3% in 1989 to 1990 to 38% in 1993 to 1994 (P<.0001). The relative frequency of documented cases of influenza in employees with symptoms of influenza decreased significantly during this period (P=.025), but nosocomial influenza rates among patients did not change significantly.

Conclusion:

A mobile-cart influenza vaccination program was associated with a significant increase in compliance among healthcare workers, but a majority still remained unvaccinated. The rate of nosocomial influenza among patients was not reduced by the modest increase in the vaccination rate, but influenza rates remained acceptably low, perhaps due to respiratory isolation of patients and furlough of employees with influenza.

Cost-effective approaches to influenza prevention and treatment

Influenza, the seventh leading cause of death in the USA, accounts for 35,000 deaths and over 200,000 hospitalizations annually in that country alone. Recent advances in influenza vaccines, diagnosis and treatment have created numerous options for practicing clinicians, as well as economic opportunities for the makers of vaccines, rapid diagnostic tests and antiviral drugs. Since influenza-like illness affects up to half of the population each year, selective use of expensive tests and treatments is essential to the practice of cost-effective medicine. Over the past 5 years, dozens of economic evaluations of influenza vaccination, rapid testing and antiviral therapy have been published, many of which are free of commercial bias. The existing literature, drawing practical lessons for clinical practice is reviewed, and new developments on the horizon are explored including vaccines, surveillance methods, antiviral agents and pandemic preparedness.

Economic evaluation of oseltamivir phosphate for postexposure prophylaxis of influenza in long-term care facilities

OBJECTIVES

To compare the cost-effectiveness of oseltamivir postexposure prophylaxis during influenza A outbreaks with that of amantadine postexposure prophylaxis or no postexposure prophylaxis in long-term care facilities (LTCFs).

DESIGN

Cost-effectiveness analysis based on decision analytic model from a government-payer perspective.

SETTING

A Canadian LTCF, with high staff vaccination, at the beginning of influenza season.

PARTICIPANTS

Elderly, influenza-vaccinated patients living in a Canadian LTCF.

MEASUREMENTS

Incremental costs (or savings) per influenza-like illness case avoided compared with usual care.

RESULTS

From a government-payer perspective, this analysis showed that oseltamivir was a dominant strategy because it was associated with the fewest influenza-like illness cases, with cost savings of $1,249 per 100 patients in 2001 Canadian dollars compared with amantadine and $3,357 per 100 patients compared with no prophylaxis. Costs for amantadine dose calculation and hospitalization for adverse events contributed to amantadine being a more-expensive prophylaxis strategy than oseltamivir. Both prophylaxis strategies were more cost-effective than no prophylaxis.

CONCLUSION

Despite high influenza vaccination rates, influenza outbreaks continue to emerge in LTCFs, necessitating cost-effective measures to further limit the spread of influenza and related complications. Although amantadine has a lower acquisition cost than oseltamivir, it is associated with more adverse events, lower efficacy, and individualized dosing requirements, leading to higher overall costs and more influenza-like illness cases than oseltamivir. Therefore the use of oseltamivir postexposure prophylaxis is more cost-effective than the current standard of care with amantadine prophylaxis or no prophylaxis.

Antiviral therapy for influenza : a clinical and economic comparative review

Each year influenza epidemics cause a considerable burden of disease. Vaccination against influenza A and B viruses has been and remains the cornerstone of influenza prevention, but antiviral therapy can serve as an important adjunct to vaccination in controlling the impact of the disease. Two classes of drugs are currently licensed in a large number of countries for the treatment of influenza. The M2 ion channel blockers or amantadanes (amantadine and rimantadine) are specific inhibitors of influenza A virus replication, whereas the neuraminidase inhibitors (zanamivir and oseltamivir) are active against influenza A and B viruses. Readily transmissible drug-resistant viruses develop frequently during amantadane treatment but not during neuraminidase inhibitor treatment. In this review, efficacy and safety data from randomised controlled trials are evaluated to gain an understanding of what we can and cannot expect from antiviral treatment. All four drugs shorten the course of influenza disease by approximately 1 day and relieve symptoms to some extent, but there is still uncertainty as to whether antiviral therapy leads to a reduction of serious complications and hospitalisation. The results of cost-effectiveness analyses are very diverse, in part because of differences in methodology but also because there is no consensus on what probabilities to assign to the key risks and benefits that form the basis of these studies. Consensus statements by advisory bodies in England and Germany recommend neuraminidase inhibitors for the therapy of influenza in high-risk individuals such as people over 65 years or under 2 years, and individuals with chronic cardiovascular, pulmonary or renal disease, diabetes mellitus or immunosuppression. However, there is no agreement as to whether antiviral therapy can be generally recommended for otherwise healthy children and adults. The availability of safe and effective antiviral therapy options should be kept in mind by the practising clinician, while more specific recommendations and policy formulation will depend on additional efficacy data that include frequency of complications and hospitalisation as outcome measures.

Safety and pharmacology of oseltamivir in clinical use

Oseltamivir is a novel agent approved for the treatment and prevention of influenza infection and illnesses in adults and children. Assessment of data from the clinical trial programme, a US health insurance database study and postmarketing surveillance allowed a comprehensive review of the safety of oseltamivir in clinical use in subjects >1 year of age. Oseltamivir has been studied over the course of a 5-year development programme in >11000 subjects from North America, Europe and the Southern Hemisphere, including otherwise healthy adults, approximately 500 elderly/high-risk subjects, and children (>1000) aged 1-12 years. Safety evaluations included treatment-emergent adverse events, hospitalisations and deaths, as well as haematological and biochemical laboratory safety tests. The data reveals that oseltamivir has simple, uncomplicated pharmacology and lacks potential for drug-drug interactions. Electrocardiogram parameters, including corrected QT interval, were unaffected by oseltamivir even at high doses. Postmarketing studies confirmed that transient gastrointestinal disturbance is the major adverse effect of oseltamivir and that this can be reduced by taking oseltamivir after a light snack. On treatment serious adverse events were reported in 1.3% of oseltamivir 75mg twice daily, 0.7% of oseltamivir 150 mg twice daily and 1.2% of placebo recipients, respectively, in the clinical trial programme. Postmarketing, it is estimated that, to date, over 4 million oseltamivir prescriptions have been dispensed worldwide. Approximately 2300 spontaneous reports were received by the manufacturer over the three winter seasons of use. As these events are reported infrequently and from an unknown number of users, it is not possible to definitively assess causality or frequency of reported events. Most reports were of gastrointestinal and skin reactions. However, a clear association between the skin reactions and oseltamivir has not been established. A large study of insurance records, which permitted the assessment of the relative risk of medical events treated in the month following prescription of oseltamivir in general use, showed no evidence of increased risk of cardiac, neuropsychiatric or respiratory events for those receiving oseltamivir compared with those who did not. To conclude, no important safety concerns have evolved which might limit the suitability of oseltamivir for the treatment and prevention of influenza in all patient populations.

Antivirals for influenza: what is their role in the older patient?

Influenza infection is a cause of high morbidity and mortality in the elderly living in the community or in long-term care facilities. Yearly immunisation is the most important means for prevention of infection. However, protection by vaccination in the elderly is incomplete, and influenza infections and outbreaks in long-term care facilities still occur. Symptoms of influenza include fever, chills, headache, myalgia and respiratory symptoms. These clinical features overlap considerably with other co-circulating respiratory viruses such as respiratory syncytial virus and parainfluenza virus. Elderly and debilitated patients with influenza may present with less prominent respiratory symptoms and may present only with fever, lassitude and confusion. Antiviral prophylaxis and treatment with amantadine and rimantadine have been given in the past but adverse effects and early development of drug resistance have limited their use. The newer antivirals zanamivir and oseltamivir are equally effective and have the advantage of being well tolerated and active against both influenza A and B without the development of resistance. However, they are costly. Early identification and diagnosis of influenza illnesses are crucial since treatment with antiviral agents should be started within 48 hours of the beginning of illness.

Use of oseltamivir during influenza outbreaks in Ontario nursing homes, 1999-2000

OBJECTIVES

To describe the experience of Ontario long-term care facilities that used oseltamivir during influenza outbreaks in 1999/2000.

DESIGN

Case series.

SETTING

Ten Ontario long-term care facilities for older people and their residents.

PARTICIPANTS

Older residents of long-term care facilities.

INTERVENTION

Oseltamivir for treatment or prophylaxis during 11 influenza outbreaks in 1999/2000.

MEASUREMENTS

Control of outbreaks; pneumonia, hospitalization, and death complicating acute influenza.

RESULTS

All outbreaks were due to influenza A//H3N2/Sydney/05/97. One facility elected to use oseltamivir for treatment and amantadine for prophylaxis. The remaining nine facilities (10 outbreaks) recommended oseltamivir for treatment and prophylaxis (after amantadine failure in five and as primary prophylaxis in five). Use of oseltamivir was associated with termination of the outbreak in all eight evaluable outbreaks. Overall, 178/185 (96%) case-residents met the case definition of influenza and had complete data for evaluation. Of these, 63 (35%) were treated with antibiotics, 37 (21%) were diagnosed with pneumonia, 19 (11%) were hospitalized, and 16 (9%) died. Compared with residents receiving no therapy or who became ill while taking amantadine, residents who received oseltamivir within 48 hours of the onset of symptoms were less likely to be prescribed antibiotics, to be hospitalized, or to die (P <.05 for each outcome). These differences persisted and remained statistically significant when corrected for influenza immunization status. A total of 730 residents received oseltamivir prophylaxis for a median of 9 days (range 5-12). Of these, side effects were identified in 30 (4.1%), the most common being diarrhea (12 residents, 1.6%), cough (5, 0.7%), confusion (4, 0.5%) and nausea (4, 0.5%).

CONCLUSIONS

Oseltamivir is safe and appears to be effective when used as treatment or prophylaxis to control outbreaks of influenza in older nursing home residents.

Amantadine's viral kinetics in chronic hepatitis C infection

Treatment for hepatitis C virus infection is limited in patients not responding to traditional therapy. Amantadine is effective for influenza infections and has been studied in patients with hepatitis C. Our aim was to determine the efficacy and safety of amantadine and to study the viral kinetics following amantadine therapy. Twelve patients with detectable HCV antibodies received amantadine 100 mg, orally twice daily. Serial HCV RNA and ALT blood samples were drawn and adverse effects were evaluated. Mean HCV RNA levels did not decrease in the first 24 hr of amantadine therapy but did decline significantly by day 3, only to rebound by day 7. All HCV RNA levels remained detectable throughout therapy and were not different from baseline values. Thirty-three percent of the patients obtained normal ALT levels after the first 24 hr of treatment and levels remained within normal range throughout the study period. More than a third of the patients discontinued therapy due to severe adverse effects occurring within one to three months after initiating treatment. In conclusion, although amantadine therapy alone was not effective, it should be considered as an adjunctive form of therapy along with interferon and ribavirin.

Long-term use of oseltamivir for the prophylaxis of influenza in a vaccinated frail older population

OBJECTIVES

To investigate the efficacy of once-daily oral oseltamivir for 6 weeks (Tamiflu) in prophylaxis against laboratory-confirmed clinical influenza in frail older subjects living in homes for seniors and to determine the safety and tolerability of long-term oseltamivir.

DESIGN

Double-blind, placebo-controlled, parallel-group, randomized, multicenter study.

SETTING

Thirty-one residential homes for seniors across United States and Europe.

PARTICIPANTS

Five hundred forty-eight frail older occupants (mean age 81 years, >80% vaccinated).

INTERVENTION

Prophylaxis with oseltamivir 75 mg or placebo once daily for 6 weeks, beginning when influenza was detected locally.

MEASUREMENTS

The primary efficacy endpoint was laboratory-confirmed clinical influenza.

RESULTS

Oseltamivir administration resulted in a 92% reduction in the incidence of laboratory-confirmed clinical influenza compared with placebo (placebo 12/272 (4.4%), oseltamivir 1/276 (0.4%); P = .002). Of subjects vaccinated against influenza, oseltamivir was 91% effective in preventing laboratory-confirmed clinical influenza (placebo 11/218 (5.0%), oseltamivir 1/222 (0.5%); P = .003). Oseltamivir use was associated with a significant reduction in the incidence of secondary complications (placebo 7/272 (2.6%), oseltamivir 1/276 (0.4%); P = .037). Although nearly all subjects were taking concomitant medication both before and during the study, oseltamivir was well tolerated. A similar incidence of adverse events, including gastrointestinal effects, occurred in both groups. There was no suppression of antibody response in oseltamivir recipients.

CONCLUSION

Oral oseltamivir 75 mg once daily for 6 weeks effectively prevented clinical influenza in vaccinated frail older subjects using significant concomitant medications in a residential care setting. The treatment was well tolerated and provided additional protection to that afforded by vaccination.

Prevention of influenza in long-term-care facilities. Long-Term-Care Committee of the Society for Healthcare Epidemiology of America

Influenza is a frequent cause of epidemic and endemic respiratory illness in long-term-care facilities (LTCFs), resulting in considerable morbidity and mortality. Detection of influenza outbreaks in this setting can be difficult, because the clinical presentation in older adults is atypical and other pathogens also cause influenza-like illness (ILI) during the influenza season. Use of the standard case definition for influenza has not been effective in detecting episodes in residents of LTCFs. Alternative case-definitions that reflect the atypical presentation of influenza in this population have been recommended but not validated. The use of rapid tests for the detection of influenza in conjunction with more sensitive case definitions of ILI may lead to the earlier detection of influenza outbreaks in LTCFs, earlier initiation of infection control measures, and reduction in transmission. The definition of outbreak, eg, the number of episodes of ILI or episodes of confirmed influenza A that would result in the initiation of antiviral chemoprophylaxis, remains controversial in this setting. The use of newer antivirals could limit the side effects seen in older adults in LTCFs. However, annual vaccination of residents and staff remains the most effective way to prevent the introduction of influenza A or influenza B into LTCFs. In addition, vaccination of LTCF residents reduces rates of illness and pneumonia due to influenza, as well as cardiopulmonary exacerbation, hospitalization, and death.

Inhibition of several strains of influenza virus in vitro and reduction of symptoms by an elderberry extract (Sambucus nigra L.) during an outbreak of influenza B Panama

A standardized elderberry extract, Sambucol (SAM), reduced hemagglutination and inhibited replication of human influenza viruses type A/Shangdong 9/93 (H3N2), A/Beijing 32/92 (H3N2), A/Texas 36/91 (H1N1), A/Singapore 6/86 (H1N1), type B/Panama 45/90, B/Yamagata 16/88, B/Ann Arbor 1/86, and of animal strains from Northern European swine and turkeys, A/Sw/Ger 2/81, A/Tur/Ger 3/91, and A/Sw/Ger 8533/91 in Madin-Darby canine kidney cells. A placebo-controlled, double blind study was carried out on a group of individuals living in an agricultural community (kibbutz) during an outbreak of influenza B/Panama in 1993. Fever, feeling of improvement, and complete cure were recorded during 6 days. Sera obtained in the acute and convalescent phases were tested for the presence of antibodies to influenza A, B, respiratory syncytial, and adenoviruses. Convalescent phase serologies showed higher mean and mean geometric hemagglutination inhibition (HI) titers to influenza B in the group treated with SAM than in the control group. A significant improvement of the symptoms, including fever, was seen in 93.3% of the cases in the SAM-treated group within 2 days, whereas in the control group 91.7% of the patients showed an improvement within 6 days (p < 0.001). A complete cure was achieved within 2 to 3 days in nearly 90% of the SAM-treated group and within at least 6 days in the placebo group (p < 0.001). No satisfactory medication to cure influenza type A and B is available. Considering the efficacy of the extract in vitro on all strains of influenza virus tested, the clinical results, its low cost, and absence of side-effects, this preparation could offer a possibility for safe treatment for influenza A and B.

Drug-induced seizures in the elderly. Causative agents and optimal management

We conducted a review of drugs that were most commonly associated with inducing seizures in the elderly population. The method for determining the risk of these agents includes evaluating the utilisation and the percentage of adverse events in previous studies and case reports. Classes of medications, such as anti-psychotics and antidepressants, are extensively reviewed to provide the clinician with treatment options in high risk patients. The risk of seizures secondary to the withdrawal of alcohol (ethanol) and benzodiazepines, and methods employed to minimise the risk are discussed. In addition, the management of patients with drug-induced seizures is delineated. Drug-induced seizures are a potentially serious adverse effect. It is important that clinicians are aware of which classes of medications and individual medications are associated with reducing seizure threshold.

Control of influenza outbreaks in the nursing home: guidelines for diagnosis and management

A well coordinated plan that includes a mechanism for surveillance, rapid antigen detection testing and viral culture, infection control techniques and chemoprophylaxis is effective for aborting outbreaks of influenza A in the nursing home. Amantadine has been better studied in this situation, and experience with rimantadine is limited. The safety and efficacy of our dose guidelines for nursing home residents need to be studied and directly compared with rimantadine dose guidelines. Except for chemoprophylaxis, these guidelines can be applied to outbreaks of influenza B as well.