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Sulphonamides: Classification, Mechanism of Action, Resistance, Therapeutic Uses, and Adverse Effects
Classification of Sulphonamides
- Based on Spectrum of Activity:
- Short-acting (e.g., Sulfadiazine, Sulfamethoxazole)
- Intermediate-acting (e.g., Sulfapyridine)
- Long-acting (e.g., Sulfasalazine, Sulfadoxine)
- Based on Clinical Use:
- Systemic sulfonamides (e.g., Sulfamethoxazole)
- Topical sulfonamides (e.g., Silver sulfadiazine)
- Combination preparations (e.g., Co-trimoxazole)
Mechanism of Action
Sulphonamides inhibit the enzyme dihydropteroate synthase, which is involved in folic acid synthesis in bacteria. By blocking this enzyme, they prevent the production of nucleic acids, thereby inhibiting bacterial growth.
Mechanism of Resistance
- Alteration of dihydropteroate synthase enzyme.
- Increased production of PABA (para-aminobenzoic acid).
- Decreased permeability of bacterial cell membrane.
- Active efflux pumps to expel sulphonamides.
Therapeutic Uses
- Urinary Tract Infections (UTIs)
- Respiratory Infections (e.g., Pneumonia, Bronchitis)
- Meningitis
- Toxoplasmosis and Malaria (e.g., Sulfadoxine-pyrimethamine)
- Topical Applications (e.g., Silver sulfadiazine for burns)
- Inflammatory Bowel Disease (IBD) (e.g., Sulfasalazine)
Adverse Effects
- Hypersensitivity reactions (e.g., rashes, Stevens-Johnson syndrome)
- Hematological effects (e.g., hemolytic anemia, leukopenia)
- Renal toxicity (e.g., crystalluria, renal failure)
- Gastrointestinal disturbances (e.g., nausea, vomiting)
- Liver toxicity (e.g., hepatitis, jaundice)
- Photosensitivity
Contraindications
- Hypersensitivity to sulphonamides
- Pregnancy (especially near term)
- Infants less than 2 months old
- G6PD deficiency
- Severe renal or hepatic impairment
