Drug inhibiting the enzyme folate synthatase is ?

Ans. is 'a' i.e., Sulfonamide SULFONAMIDES Sulfonamides are bacteriostatic and act by inhibiting folic acid synthesis by inhibiting enzyme folate synthatase. Bacteria synthesize their own folic acid of which para aminobenzoic acid (PABA) is a constituent - Sulfonamides, being structural analogues of PABA, inhibit bacterial folate synthase competitively. 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. Classsification Sho acting - Sulfadiazine, Sulfisoxaxole, Sulfamethizole, Sulfacystine. 2.Intermediate acting - Sulfamethoxazole. Long acting - Sulfadoxine, Sulfamethopyrazine. Topical Sulfonamides - Sulfacetamide sodium, Mafenide, silver sulfadiazine. Sulfonamide for RA and ulcerative colitis - Sulfasalazine. Adverse effects Most common adverse effects are due to hypersensitivity - Drug fever, Skin rashes, exfoliative dermatitis, Photosensitivity, uicaria, nausea, vomiting and diarrhea - Katzung 10th/e p. 764. Crystalluria, Hepatitis, hemolysis in G-6-PD deficiency, kernicterus in newborn are other side effects. Primary pathwary of metabolism of Sulfonamides is acetylation. The acetylated derivative is less soluble in acidic urine - may precipitate and cause crystalluria.