Sulphonamides: MOA, Uses, Side effects-NotesMed

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Introduction of sulphonamides

Sulphonamides are the first effective antimicrobial agents. They are most commonly used in the treatment of bacterial infections in men. Sulphonamides are derivatives of Sulphanilamide (para-aminobenzene sulphonamide).

Classifications of drug

They are following classification are shown below

  • Systemic acting agents
    • Short-acting (4-8 hrs): Sulphadiazine
    • Intermediate-acting (8-12 hrs): Sulphamethoxazole
    • Long-acting (> 7 days): Sulphadoxine
  • Local acting agents
    • Sulfacetamide
    • Silver sulphadiazine
    • Mafenide
  • Others:–Sulphasalazine (acts both locally and systemically).

Mechanism of action of sulphonamides

Para-aminobenzoic acid (PABA) is a precursor of compound folic acid. Para-aminobenzoic acid (PABA) is essential for the growth and multiplication of bacteria. Sulphonamides are structurally similar to para-aminobenzoic acid (PABA).

The drugs competitively inhibit folate synthetase enzyme and prevent the formation of folic acid. Drugs producing bacteriostatic effect but not effective in the presence of pus as it is rich in para-aminobenzoic acid (PABA), purine, and thymidine.



It is well absorbed from the gut and bound to plasma proteins, particularly albumin. It the distributed in almost all tissues of the body such as CSF. It crosses the placental barrier and reaches fetal circulation. The drugs are metabolized in the liver mainly by acetylation and excreted partly unchanged and partly as metabolic products.

Adverse effects (@ AKC of RESH)

  • Acute hemolytic anemia (due to glucose-6-phosphate dehydrogenase deficiency)
  • Kernicterus:
    • In neonates, specifically in premature babies, may cause displacement of bilirubin from plasma proteins.
    • Free bilirubin can cross the blood-brain barrier & get deposited or settled in the basal ganglia.
  • Crystalluria
  • Hypersensitivity reactions include itching, skin rashes, drug fever, and Exfoliative dermatitis
  • Stevens-Johnson syndrome
  • Haematuria or obstruction to urinary tract
  • May cause Hepatitis and bone marrow suppression.

Drugs interactions

Methotrexate, Phenytoin, oral anticoagulant drugs, and oral hypoglycaemic agents (such as sulfonylureas)-inhibiting their metabolism and displacing them from plasma protein binding sites.

Uses of sulphonamides

  • Chloroquine-resistant Plasmodium falciparum malaria
  • Toxoplasmosis
  • Nocardiosis
  • Treatment of P.jiroveci infection in patients with AIDS
  • Ophthalmic infections
  • Inflammatory bowel disease
  • Rheumatoid arthritis
  • Prophylaxis of Rheumatic fever.
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