A pyrimidine inhibitor of dihydrofolate reductase, it is an antibacterial related to pyrimethamine. The interference with folic acid metabolism may cause a depression of hematopoiesis. It is potentiated by sulfonamides and the trimethoprim-sulfamethoxazole combination is the form most often used. It is sometimes used alone as an antimalarial.
This definition is at least in part based on: Anonymous (2015), Trimethoprim (English). Medical Subject Headings. U.S. National Library of Medicine.