The activity of atovaquone (566C80) in murine toxoplasmosis is markedly augmented when used in combination with pyrimethamine or sulfadiazine.

The activity of atovaquone in the treatment of murine toxoplasmosis was greatly enhanced when administered in combination with pyrimethamine or sulfadiazine. Mice infected with lethal inocula of tachyzoites or cysts of Toxoplasma gondii and treated with doses of atovaquone, pyrimethamine, or sulfadiazine that were ineffective when administered alone had 70% survival when pyrimethamine plus atovaquone and 100% survival when sulfadiazine plus atovaquone was used. Of interest, doses of pyrimethamine and, particularly, sulfadiazine far below the doses that would induce any protection in infected mice were active when combined with atovaquone. These results suggest that clinical trials for treatment of toxoplasmosis in AIDS patients using the combination of atovaquone with sulfadiazine or pyrimethamine are justified.