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.