Pyrimethamine is a medication primarily used to treat and prevent toxoplasmosis, a parasitic infection caused by the Toxoplasma gondii parasite. It works by inhibiting the synthesis of folic acid in the parasite, which is essential for its growth and reproduction. Pyrimethamine is often prescribed in combination with sulfadiazine or clindamycin to enhance its effectiveness. In addition to treating toxoplasmosis, pyrimethamine is also used in the management of malaria, particularly in areas where resistance to other antimalarial drugs is common. It is important for patients to follow their healthcare provider's instructions regarding dosage and duration of treatment to minimize potential side effects.