Activities of pefloxacin and ciprofloxacin against experimental malaria in mice.

We investigated the in vivo antimalarial activities of pefloxacin and ciprofloxacin in Swiss albino mice infected intravenously with 5 x 10(6) Plasmodium yoelii N67 parasites 1 h before treatment. Groups of 20 mice received a subcutaneous injection of 40, 80, or 160 mg of ciprofloxacin or pefloxacin per kg of body weight every 8 h for 3 days. Parasitologic activity was assessed on day 4, and survival was assessed on day 21. Control mice had a fulminant course with a parasitemia of 61.3% +/- 12.1% on day 4, and 90% of the mice were dead on day 21. The lower dosages of pefloxacin and ciprofloxacin (40 and 80 mg/kg) were not efficient. With 160 mg/kg, ciprofloxacin achieved an 85.8% reduction in parasitemia and 17 of 20 mice survived. Pefloxacin achieved a 92.8% reduction in parasitemia, and all mice survived. All treated, noninfected control mice survived. With ciprofloxacin, the antimalarial activity was similar with injections of 240 mg/kg every 12 h but was strongly diminished with injections of 160 mg/kg every 12 h. With pefloxacin, similar activities were observed with injections of 160 mg/kg every 8 h or injections of 160 or 240 mg/kg every 12 h. With both drugs, this activity was highly reduced when the treatment was delayed by 24 h. This underlines the need to provide treatment within the first hours after infection to achieve an optimal effect in this rapidly lethal experimental model of malaria. Pefloxacin and, to a lesser extent, ciprofloxacin are potent antimalarial drugs which might prove useful in the treatment of less rapidly aggressive human malaria.