Safety and prophylactic efficacy of low-dose rimantadine in adults during an influenza A epidemic.

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.