Longest acting sulphonamide is -

Ans, is 'd' i.e., Sulfadoxine Sulfonamideso Sulfonamides are bacteriostatic and act by inhibiting folic acid synthesis by inhibiting enzyme folate synthatase.o Bacteria synthesize their own folic acid of wTtich para aminobenzoic acid (PABA) is a constituent - Sulfonamides, being structural analogues of PABA, inhibit bacterial folate synthase competitively.o Sulfonamides are not effective in presence of pus and tissue extract because - (1) Pus contains purines and thymidine which decrease bacterial requirement for folic acid and (2) Pus is rich in PABA.Classification1. Short acting - Sulfadiazine, Sulfisoxaxole, Sulfamethizole, Sulfacystine.Intermediate acting - Sulfamethoxazole.Long acting - Sulfadoxine, Sulfamethopyrazine.Topical Sulfonamides - Sulfacetamide sodium, Mafenide, silver sulfadiazine.Sulfonamide for RA and ulcerative colitis - Sulfasalazine.o Sulfadoxine is Longest acting whereas sulfacytidine is shortest acting sulphonamide.