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Home / Drugs / Starting with S / Sulfamethizole


For the treatment of urinary tract infection


Sulfamethizole is a sulfonamide antibiotic. The sulfonamides are synthetic bacteriostatic antibiotics with a wide spectrum against most gram-positive and many gram-negative organisms. However, many strains of an individual species may be resistant. Sulfonamides inhibit multiplication of bacteria by acting as competitive inhibitors of p-aminobenzoic acid in the folic acid metabolism cycle. Bacterial sensitivity is the same for the various sulfonamides, and resistance to one sulfonamide indicates resistance to all. Most sulfonamides are readily absorbed orally. However, parenteral administration is difficult, since the soluble sulfonamide salts are highly alkaline and irritating to the tissues. The sulfonamides are widely distributed throughout all tissues. High levels are achieved in pleural, peritoneal, synovial, and ocular fluids. Although these drugs are no longer used to treat meningitis, CSF levels are high in meningeal infections. Their antibacterial action is inhibited by pus.

mechanism of action

Sulfamethizole is a competitive inhibitor of bacterial enzyme dihydropteroate synthetase. The normal para-aminobenzoic acid (PABA) substrate is prevented from binding. The inhibited reaction is necessary in these organisms for the synthesis of folic acid.




Rapidly absorbed.

half life

3-8 hours

drug interactions

Chlorpropamide: Sulfonamide/sulfonylurea: possible hypoglycemia

Fosphenytoin: The sulfonamide increases the effect of hydantoin

Methotrexate: The sulfamide increases the toxicity of methotrexate

Phenytoin: The sulfonamide increases the effect of hydantoin