A synthetic derivative of ethyl-pyrimidine with potent antimalarial properties. Pyrimethamine is a competitive inhibitor of dihydrofolate reductase (DHFR). DHFR is a key enzyme in the redox cycle for production of tetrahydrofolate, a cofactor that is required for the synthesis of DNA and proteins. This agent is often used in combination with other antimalarials for the treatment of uncomplicated falciparum malaria. Check for active clinical trials using this agent. (NCI Thesaurus)