RYCLORA

Dexchlorpheniramine, the d-isomer of the racemic compound chlorpheniramine, is two times more active than chlorpheniramine. Dexchlorpheniramine does not prevent the release of histamine, but rather, competes with free histamine for binding at the H₁-receptor sites, and competitively antagonizes the effects of histamine on H₁-receptors in the GI tract, uterus, large blood vessels, and bronchial muscle. Blockade of H₁-receptors also suppresses the formation of oedema, flare, and pruritus that result from histaminic activity. Since dexchlorpheniramine binds to central and peripheral H₁-receptors, sedative effects are likely to occur. Dexchlorpheniramine has high antihistaminic activity, moderate anticholinergic effects and minimal sedative effects.