In vitro activity of cotrimoxazole on the intracellular multiplication of Toxoplasma gondii.

Cotrimoxazole, from 60 mug/ml, inhibited the replication of Toxoplasma gondii within Hela cells and mouse peritoneal macrophages. The percentage of inhibition reached practically 100% after 18 hours of treatment at 37 degrees C. More prolonged treatment resulted in an eradication of the organisms from the cell monolayers. In contrast, similar doses of spiramycin were quite ineffective against intracellular toxoplasma. The active doses of cotrimoxazole used were not harmful for cell cultures. Cotrimoxazole also destroyed clones (rosaces) of toxoplasma which were formed during the past 18 hours of intracellular replication in the absence of the drug. Trimethoprim was the only effective compound of cotrimoxazole on intracellular parasites; the adjunction of sulfamethoxazole produced a marked synergistic effect. The present findings confirm the great efficiency of cotrimoxazole in the treatment of experimental toxoplasmosis in mice performed previously in this laboratory.