Written by the Fiveable Content Team • Last updated September 2025
Written by the Fiveable Content Team • Last updated September 2025
Definition
Pyrimethamine is an antiparasitic drug primarily used to treat toxoplasmosis and malaria. It works by inhibiting dihydrofolate reductase, an enzyme necessary for the replication of protozoal DNA.
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Pyrimethamine is often combined with sulfadiazine to enhance its efficacy against Toxoplasma gondii.
The drug can cause side effects such as bone marrow suppression, which necessitates monitoring blood cell counts during treatment.
Pyrimethamine is classified as a folic acid antagonist because it disrupts the production of tetrahydrofolic acid in parasites.
It has been used both in prophylaxis and treatment of malaria, particularly for strains resistant to other antimalarial drugs.
Resistance to pyrimethamine can occur through mutations in the dihydrofolate reductase gene of the parasite.