Effects of spiramycine and pyridazine were evaluated on experimental toxoplasmosis in mice infected with Beverley or RH strains, comparing with those of pyrimethamine which is known to have potent action to toxoplasma. Spiramycine and pyridazine, when used alone, showed slight killing effects on toxoplasma, although the survival period of mice was prolonged considerably.
Combined use of these two drugs proved effective in oral administration of 13 mg each per mouse, if given immediately after infection for 21 days, demonstrating no viable toxoplasma in almost all mice, experimentally infected.
Therapeutic effects of combinations of these two drugs was almost equivalent to these of pyrimethamine. The two strains of toxoplasma used, Beverley and RH, did not show any differences in susceptibility to these drugs, but this might be due to the fact that relatively enormous dosages of the drugs were administered.