Drug inhibiting the enzyme folate synthatase is ?
Sulfonamide
Clindamycin
Rifampicin
Norfloxacin
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.