Anatomical Therapeutic Chemical Classification System
Sulfadiazine is an antibiotic that belongs to the class of drugs known as sulphonamides. Sulfadiazine is a structural analogue and competitive antagonist of p-aminobenzoic acid preventing bacterial utilisation of PABA in the synthesis of folic acid.
Sulfamethoxazole competitively inhibits the utilisation of para-aminobenzoic acid in the synthesis of dihydrofolate by the bacterial cell resulting in bacteriostasis.
Trimethoprim is a dihydrofolate reductase inhibitor which affects the nucleoprotein metabolism of micro-organisms by interference in the folic-folinic acid systems, inhibiting the conversion of bacterial dihydrofolic acid to tetrahydrofolic acid, required for the synthesis of some amino acids. Its effects are considerably greater on the cells of microorganisms than on the mammalian cells. Trimethoprim may be bactericidal or bacteriostatic depending on growth conditions.