Sulfacytine is a short-acting sulfonamide, which was used for the treatment uncomplicated urinary tract infections, but was discontinued. This drug is a is a competitive inhibitor of the dihydropteroate synthetase, that inhibits bacterial synthesis of dihydrofolic acid by preventing the condensation of the peridine with para-aminobenzoic acid (PABA), a substrate of the enzyme dihydropteroate synthetase.