Comparison of central nervous system adverse effects of amantadine and rimantadine used as sequential prophylaxis of influenza A in elderly nursing home patients

Background: Amantadine hydrochloride and rimantadine hydrochloride are reco mmended by the Centers for Disease Control and Prevention for prophylaxis o f influenza A. While data suggest that rimantadine is better tolerated, the re are no data examining the rate of adverse reactions in elderly patients who receive amantadine vs rimantadine. Our objective was to assess the adve rse reaction rate in elderly nursing home patients receiving sequential ama ntadine and rimantadine for influenza A prophylaxis. Methods: Data were collected in 156 nursing home patients (70% women; mean/-SD age, 83.7+/-10.1 years) in a single care setting who received sequenti al therapy with amantadine and rimantadine during the 1997-1998 influenza s eason. Patients were assessed for central nervous system adverse effects an d therapy discontinuation occurring with each agent. Results: Twenty-nine (18.6%) of the 156 patients experienced an adverse eff ect when receiving amantadine compared with 3 patients (1.9%) when rimantad ine was given (P<.01). Drug use was discontinued due to adverse events in 1 7.3% (n = 27) of the amantadine courses and 1.9% (n=3) of the rimantadine c ourses (P<.001). Confusion was the most frequently observed adverse event ( amantadine, 10.6%; rimantadine, 0.6%; P<.001). Multivariate logistic regres sion analysis showed that significant risk factors for central nervous syst em adverse events included male sex (odds ratio, 3.65), reduced calculated creatinine clearance (odds ratio, 1.78), and use of amantadine (odds ratio, 12.73). Conclusions: Amantadine use was associated with a significantly higher inci dence of central nervous system adverse events than rimantadine use in this elderly population receiving influenza prophylaxis. In addition, the disco ntinuation rate of amantadine was significantly higher than that with riman tadine.