Purpose: To evaluate the efficacy and safety of amantadine and rimantadine, the first generation antivirals, for the prophylaxis of influenza virus.
Data sources: A systematic search of the English language literature using MEDLINE, EMBASE, Current Contents and the Cochrane database from 1966 to April 2002, as well as a manual search of references from retrieved articles, were performed.
Study selection: Prospective, randomized, controlled clinical trials evaluating amantadine and rimantadine for prophylaxis of naturally occurring influenza A illness were considered. The control arm used either a placebo or an antiviral agent.
Data extraction: Each trial was assessed by two authors to determine the adequacy of randomization and description of withdrawals. Efficacy data were extracted according to a predefined protocol. Discrepancies in data extraction among the investigators were solved by consensus. Nine prophylaxis studies of amantadine and rimantadine met the criteria for this systematic review.
Data synthesis: Seven amantadine versus placebo trials (n=1797), three rimantadine versus placebo trials (n=688) and two amantadine versus rimantadine studies (n=455) were included for the meta-analysis on the prevention of influenza A illness. The summary of results for the relative odds of illness indicated a 64% reduction in the amantadine group compared with placebo (OR 0.36, 95% CI 0.23 to 0.55, P< or =0.001), a 75% reduction in illness for the rimantadine group compared with placebo (OR 0.25, 95% CI 0.07 to 0.97, P=0.05) and no significant differences in the odds of illness for the amantadine versus rimantadine groups (OR 1.15, 95% CI 0.57 to 2.32, P=0.32). The summary of results examining adverse events showed significantly higher odds of central nervous system adverse reactions and premature withdrawal from the clinical trials in the amantadine-treated group than in the placebo-treated group. Compared with the placebo-treated group, the rimantadine-treated group did not have a significantly higher rate of withdrawal or central nervous system events. However, there was a significant increase in the odds of gastrointestinal adverse events for those treated with rimantadine compared with those treated with placebo (OR 3.34, 95% CI 1.17 to 9.55, P=0.03). In the comparative trials of amantadine to rimantadine, rimantadine was associated with an 82% reduction in the odds of central nervous system events (OR 0.18, 95% CI 0.03 to 1.00, P=0.05) and a 60% reduction in the odds of discontinuing treatment (OR 0.40, 95% CI 0.20 to 0.79, P=0.009).
Conclusion: This meta-analysis demonstrates that amantadine and rimantadine are superior to placebo in the prevention of influenza A illness. Both antiviral agents have an increased number of adverse events compared with placebo; however, the use of amantadine is associated with significantly higher numbers of central nervous system events and treatment withdrawals compared with rimantadine. Thus, rimantadine should be the preferred agent in this class for the prevention of influenza A virus infection and should be made available in Canada.