Rimantadine and oseltamivir demonstrate synergistic combination effect in an experimental infection with type A (H3N2) influenza virus in mice

We studied the combination effect of rimantadine hydrochloride and oseltamivir phosphate on mice infected with influenza A/Aichi/2/68 (H3N2) virus. Compounds were simultaneously administered in a 5-day-treatment course, starting 4 h before intranasal infection with 10 or 20 viral 50% mouse lethal doses. Initially, we tested combinations of oseltamivir (0.05, 0.1 and 0.2 mg/kg/day) and rimantadine (2.5, 5.0 and 7.5 mg/kg/day). Significant differences were recorded between combination-treated groups, and groups with separately applied compounds and the placebo group, such as: protection index of oseltamivir with 5.0 or 7.5 mg/kg rimantadine varied between 34-41% and 43-87%, respectively, whereas the individual effects of oseltamivir, 5 mg/kg of rimantadine and 7.5 mg/kg of rimantadine were 0-10%, 0% and 18.7-29.6%, respectively; mean survival time in combination-treated groups was lengthened by 3.1-6.9 days, in oseltamivir groups by 0-1.9 days, and in rimantadine groups by 0.8-1.3 days at 5 mg/kg and 2.6-3.2 days at 7.5 mg/kg. The three-dimensional method of Prichard and Shipman characterized the combination effect as synergistic. Further, we studied the activity of 0.05 mg/kg/day of oseltamivir combined with 5 mg/kg of rimantadi...Continue Reading