About sulphacetamide sodiumsulfonamide, anti-infective.mechanism of action of sulphacetamide sodiumsulphacetamide sodium is a sterile, topical sulfonamide which exerts its bacteriostatic action by inhibiting bacterial folate synthetase enzyme and results in inhibition of bacterial folic acid synthesis. sulfonamides are structural analogues of paba (para amino benzoic acid) which is an essential constituent of bacterial folic acid. it competitively inhibits the incorporation of paba with pteridine residue to form dihydropteroic acid which conjugates with glutamic acid and produce dihydrofolic acid. also being chemically similar to paba the sulfonamides may itself incorporated to form an altered folate which is metabolically injurious