Antifols: Pyrimethamine and Sulfonamides clinical use

Combination of pyrimethamine with sulfadiazine has synergistic activity against Toxoplasma gondii through the sequential blockade of 2 steps in folic acid synthesis. Pyrimethamine plus clindamycin (or sulfadiazine) is a regimen of choice for prophylaxis against and treatment of toxoplasmosis. For treatment of active toxoplasmosis, the drug combination is given daily for 3–4 wk, with folinic acid to offset hematologic toxicity. For Toxoplasma encephalitis in AIDS, high-dose treatment with pyrimethamine plus sulfadiazine (or  clindamycin) plus folinic acid must be maintained for at least 6 wk.