Sulphadimidine Sodium have a similar structure to P-amino benzoic acid and to interfere with the synthesis of nucleic acids in sensitive microorganism by blocking the conversion of
P-amino benzoic acid to the co-enzyme dihydrofoloic acid, a reduced form of folic acid. Their action is primarily bacteriostatic, although they may be bactericidal where concentrations of thymine are low in the surrounding medium. Sulphonamides have a broad spectrum of action, but the development of widespread resistance has greatly reduced their usefulness, and susceptibility often varies widely even among nominally sensitive pathogens
