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  • Title: Chlorpheniramine plasma concentration and histamine H1-receptor occupancy.
    Author: Yasuda SU, Wellstein A, Likhari P, Barbey JT, Woosley RL.
    Journal: Clin Pharmacol Ther; 1995 Aug; 58(2):210-20. PubMed ID: 7648771.
    Abstract:
    The plasma concentration-response relationship of the antihistamine chlorpheniramine is poorly characterized. This study examined concurrently the concentrations of chlorpheniramine and presence of H1-receptor antagonist in plasma after administration of 8 mg chlorpheniramine in normal volunteers. Six extensive metabolizers and five poor metabolizers, as judged by CYP2D6 phenotype (dextromethorphan metabolic ratio), were enrolled in the study. More than 80% occupancy of H1-receptors by antagonist in plasma was observed for 12 hours after the dose in extensive metabolizers and greater than 60% from 12 to 30 hours in poor metabolizers, when plasma concentrations had fallen below those that should result in 50% occupancy of receptors. The results suggest that (+/-)-chlorpheniramine plasma concentrations do not predict H1-receptor antagonist in plasma. In addition, a role is suggested for CYP2D6 in formation of a potent active metabolite of chlorpheniramine.
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