Sulphacetamide Sodium is a short-acting, bacteriostatic sulfonamide antibiotic primarily used topically in ophthalmology and dermatology. It is a derivative of sulfanilamide with high solubility, allowing for effective topical application. In the Indian context, it is a cornerstone treatment for superficial bacterial infections of the eye and skin, valued for its efficacy, low cost, and wide availability.
Adult: Ophthalmic: Instill 1-2 drops into the affected eye(s) every 2-3 hours during the day, less frequently at night, initially. Frequency may be reduced as infection improves. Topical Dermatological: Apply a thin layer to affected skin 2-4 times daily.
Note: Ophthalmic: Wash hands. Tilt head back, pull lower eyelid down to form a pouch. Instill drops without touching the dropper tip. Close eyes gently for 1-2 minutes. Apply finger pressure to the lacrimal sac (inner corner of eye) for 1 minute to minimize systemic absorption. Dermatological: Clean and dry area before application. Use sparingly. Do not use occlusive dressings unless directed.
Sulphacetamide is a competitive antagonist of para-aminobenzoic acid (PABA). It inhibits the bacterial enzyme dihydropteroate synthase. This prevents the incorporation of PABA into dihydrofolic acid, a precursor of folic acid. Bacteria susceptible to sulphacetamide must synthesize their own folic acid; mammalian cells utilize preformed folate and are thus unaffected by this mechanism.
Pregnancy: Category C (US FDA). No adequate and well-controlled studies in pregnant women. Use only if the potential benefit justifies the potential risk to the fetus. Systemic sulfonamides cross the placenta and can cause kernicterus in the newborn if used near term. Topical use with minimal absorption is generally considered low risk.
Driving: May cause transient blurred vision immediately after ophthalmic instillation. Patients should not drive or operate machinery until vision clears.
| Silver-containing preparations (e.g., Silver sulfadiazine) | Incompatible; forms precipitates, inactivating both agents. | Major |
| Para-aminobenzoic acid (PABA) containing products | PABA antagonizes the antibacterial effect of sulphacetamide. | Major |
| Local Anesthetics (e.g., Procaine, Tetracaine) | Metabolized to PABA, may antagonize sulphacetamide effect. | Moderate |
| Oral Sulfonylureas (e.g., Glipizide) | Theoretical risk of cross-sensitivity; no direct pharmacokinetic interaction with topical use. | Minor |
| Methotrexate | Increased risk of methotrexate toxicity due to displacement from plasma protein binding (relevant only with systemic absorption). | Moderate |
Same composition (Sulphacetamide (NA)), different brands: