Evaluation of the antimuscarinic activity of atropine, terfenadine and mequitazine in healthy volunteers.

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Abstract
1 The anticholinergic effects of atropine and two antihistamines (terfenadine and mequitazine) were investigated vs placebo is a double-blind study. 2 Salivary secretion, basal pupil diameter, pilocarpine (0.25%) induced miosis and heart rate were determined in eight healthy volunteers, seven male and one female, aged between 23 and 35 years. Each volunteer received all four separate courses of treatment: i.e., terfenadine 60 mg or mequitazine 5 mg twice daily for 3 days, and one single dose on the day of the trial; for the placebo or atropine courses they received the placebo twice daily during 3 days and, on the morning of test day, either the placebo again or atropine 1 mg. Pupillary diameter was measured under standardized conditions using a pupil gauge (Smith and Nephew Pharmaceuticals Ltd). 3 Atropine significantly reduced salivary output (-2.25 .+-. 0.36 ml from control values of 4.17 .+-. 0.42 ml, P < 0.001) and heart rate (-9.7 .+-. 3.7 beats min-1 from 77.5 .+-. 2.7, P < 0.05). These maximal effects were observed 3 h after atropine dosing for salivary secretion and 1 h for heart rate. Atropine did not affect basal pupil diameter or pilocarpine-induced miosis. 4 Mequitazine and terfenadine did not affect salivary flow, heart rate or pilocarpine-induced miosis. 5 Terfenadine and mequitazine had no anticholinergic effect in these tests involving a limited number of subjects.