Source:http://linkedlifedata.com/resource/umls/id/C0724713
NCI: The sulfate salt form of trimethoprim, a synthetic substituted pyrimidine with antibacterial activity. Trimethoprim sulfate selectively binds to and reversibly inhibits dihydrofolate reductase, thereby blocking the production of tetrahydrofolic acid from dihydrofolic acid. This leads to an inhibition of bacterial synthesis of folic acid, thereby affecting nucleic acid and protein synthesis. Trimethoprim sulfate has a stronger binding affinity for the bacterial enzyme than for the corresponding mammalian enzyme.