Used primarily to treat and prevent protozoal infections, especially malaria and toxoplasmosis. It works by inhibiting dihydrofolate reductase, an enzyme essential for parasite DNA synthesis. Commonly used in combination with sulfadoxine for malaria treatment, where it helps reduce parasite resistance development. In immunocompromised patients, such as those with HIV, it is used alongside other agents to manage toxoplasmic encephalitis. Also used in veterinary medicine for treating coccidiosis in animals. Its role in antiparasitic therapy makes it valuable in both acute treatment and long-term prophylaxis in high-risk populations.