In double-blind placebo-controlled studies of 404 volunteers, amantadine hydrochloride was found to be 51% effective in preventing the development of artificially induced A2 influenza, and 73% to 92% effective in preventing the more severe form of A2 influenza. Milder disease was seen in those who developed A2 influenza in spite of amantadine therapy. Serological responses were also reduced. No significant difference was observed either between once- and twice-daily dosage or between 200 mg and 100 mg/day regimens. No benefit was observed when the start of medication was delayed until symptoms of influenza developed. Amantadine was ineffective against B influenza. No safety problem was evident in any subject.
Smorodintsev AA, Zlydnikov DM, Kiseleva AM, Romanov JA, Kazantsev AP, Rumovsky VI. Evaluation of Amantadine in Artificially Induced A2 and B Influenza. JAMA. 1970;213(9):1448-1454. doi:10.1001/jama.1970.03170350016003