Plasmodium yoelii: activity of azithromycin in combination with pyrimethamine or sulfadoxine against blood and sporozoite induced infections in Swiss mice

The efficacy of pyrimethamine or sulfadoxine administered in combination with azithromycin was examined in a rodent malaria model. Outbred Swiss mice infected with blood stage parasites were treated from day 0 to day 3 and efficacy of different regimens was monitored in terms of the curative response and the delay time to reach 2% parasitaemia (2% DT). Administration of azithromycin alone at 60 mg/kg/day produced curative response while lower doses showed marginally delayed 2% DT. A marked potentiation in activities of pyrimethamine (100-fold) or sulfadoxine (10-fold) was observed when administered at non-curative doses of 0.1 mg/kg/day in combination with azithromycin (30 mg/kg/day) against blood stage parasites. A combination of 10 mg/kg/day azithromycin with 0.3 mg/kg/day sulfadoxine was also curative. Likewise in the causal prophylactic test, a combination regimen comprising 1/16th and 1/3rd the individual curative doses of pyrimethamine and azithromycin, respectively, prevented the development of patent Infection after Plasmodium yoelii sporozoite challenge. Our results suggest that a combination of azithromycin with the second line treatment regimen of fansidar may enhance the therapeutic efficacy of the latter and also provide better prophylaxis against Plasmodium falciparum malaria.