Wiktionary
pyrimethamine
n. (context medicine English) a folic acid antagonist, used in the prophylactic treatment of malaria
Wikipedia
Pyrimethamine
Pyrimethamine (trade name Daraprim) is a medication used for protozoal infections. It is commonly used as an antimalarial drug (for both treatment and prevention of malaria), and to treat Toxoplasma gondii infections, particularly when combined with the sulfonamide antibiotic sulfadiazine when treating HIV-positive individuals. It works by inhibiting folic acid metabolism via dihydrofolate reductase.
It is on the World Health Organization's List of Essential Medicines, the most important medications needed in a basic health system.