Sulphacetamide (20% w/v) + Chlorpheniramine Maleate (0.5% w/v) (Medical Monograph)

Overview

A fixed-dose ophthalmic solution combining a bacteriostatic sulfonamide antibiotic (Sulphacetamide) with a first-generation alkylamine antihistamine (Chlorpheniramine Maleate). It is primarily indicated for the treatment of superficial bacterial conjunctivitis and associated allergic symptoms like itching and redness. Sulphacetamide inhibits bacterial folate synthesis, while Chlorpheniramine antagonizes histamine H1 receptors, providing symptomatic relief from pruritus and inflammation.

Sulphacetamide is a competitive antagonist of para-aminobenzoic acid (PABA), inhibiting the bacterial enzyme dihydropteroate synthase. This prevents the synthesis of dihydrofolic acid, a precursor for tetrahydrofolic acid, which is essential for bacterial DNA and protein synthesis. Chlorpheniramine Maleate is a potent competitive inverse agonist at histamine H1 receptors, blocking the effects of histamine released during allergic reactions, thereby reducing vascular permeability, itching, and erythema.