Sulphacetamide Sodium (20% w/v) is a topical antibacterial agent belonging to the sulfonamide class. It is primarily used in ophthalmology for the treatment and prophylaxis of superficial ocular infections caused by susceptible microorganisms, including conjunctivitis and corneal ulcers. It acts as a competitive antagonist of para-aminobenzoic acid (PABA), inhibiting bacterial dihydropteroate synthase and thus folate synthesis. In the Indian market, it is widely available as eye drops and eye ointment, often in combination with other agents like corticosteroids for enhanced anti-inflammatory effect.
Adult: One to two drops into the affected eye(s) every 2-3 hours during the day, with less frequent application at night (e.g., every 4-6 hours). For ointment: Apply a small ribbon (approx. 1 cm) into the lower conjunctival sac 3-4 times daily and at bedtime. Frequency may be reduced as infection improves.
Note: 1. Wash hands before use. 2. Tilt head back, pull down lower eyelid to form a pouch. 3. Instill the prescribed number of drops without touching the dropper tip to the eye, eyelid, or any surface. 4. Close eyes gently for 1-2 minutes, applying gentle pressure to the nasolacrimal duct (inner corner of eye) to minimize systemic absorption. 5. Wait at least 5-10 minutes before instilling any other eye medication. For ointment: Apply in the same manner, then close eyes and roll them to spread the ointment. Vision may be blurred temporarily.
Sulphacetamide is a bacteriostatic antibiotic. It is a structural analogue of para-aminobenzoic acid (PABA). It competitively inhibits the bacterial enzyme dihydropteroate synthase. This inhibition prevents the incorporation of PABA into dihydrofolic acid (folic acid), a crucial precursor for the synthesis of purines and pyrimidines required for bacterial DNA and RNA synthesis.
Pregnancy: Pregnancy Category C (US FDA). Animal reproduction studies have not been conducted with topical sulphacetamide. It is not known whether it can cause fetal harm when applied topically. Use during pregnancy only if the potential benefit justifies the potential risk to the fetus. Minimal systemic absorption is expected.
Driving: May cause transient blurring of vision immediately after instillation, especially the ointment form. Patients should not drive or operate machinery until vision clears.
| Silver preparations (e.g., Silver Nitrate) | Incompatible; forms insoluble silver sulphacetamide precipitate. | Major |
| Local Anesthetics (e.g., Procaine, Tetracaine) | Procaine is a PABA derivative and may antagonize the antibacterial effect of sulphacetamide. | Moderate |
| Oral Sulfonamides (e.g., Cotrimoxazole) | Increased risk of systemic sulfonamide toxicity and cross-hypersensitivity. | Moderate |
| Warfarin | Theoretically, systemic absorption could potentiate warfarin effect by displacing it from protein binding sites. Monitor INR if used extensively on damaged cornea. | Moderate |
Same composition (Sulphacetamide (20% w/v)), different brands: