Affinities of brompheniramine, chlorpheniramine, and terfenadine at the five human muscarinic cholinergic receptor subtypes

Anticholinergic effects are presumed to be the mechanism for the efficacy o f chlorpheniramine in symptomatic relief of the common cold. Terfenadine, a second-generation antihistamine, reportedly lacks anticholinergic side eff ects. We evaluated affinities of two commonly used over-the-counter antihis tamines, brompheniramine and chlorpheniramine, as well as terfenadine in co mparison with atropine at the five human muscarinic cholinergic receptor su btypes using CHO cells stably transfected with the individual subtypes. Atr opine was more potent than all three drugs at m1-m5 (p<0.01). No significan t difference was observed between chlorpheniramine and brompheniramine. Atr opine, brompheniramine, and chlorpheniramine could not discriminate between m1-m5. Terfenadine demonstrated subtype selectivity at m3. In vitro compar isons in human muscarinic receptor subtypes could potentially be used to pr edict clinical anticholinergic effects of antihistamines and to target rece ptor-specific effects of such agents.