Pyrimethamine

Pyrimethamine is a dihydrofolate reductase (DHFR) inhibitor with an IC50 of 15.4 nM. It is a medication used for protozoal infections. It is commonly used as an antimalarial drug (for both treatment and prevention of malaria), and is also used (combined with sulfadiazine) in the treatment of Toxoplasma gondii infections in immune-compromised patients, such as HIV-positive individuals. It interferes with folic acid synthesis by inhibiting the enzyme dihydrofolate reductase (DHFR). Folic acid is needed for DNA and RNA synthesis in many species, including protozoa.