Integrated pharmacokinetics and pharmacodynamics of atropine in healthy humans. I: Pharmacokinetics

Abstract

The pharmacokinetics of atropine in three healthy male volunteers after intravenous administration of 1.35 and 2.15 mg of the drug was determined. Pharmacodynamic effects of atropine were measured simultaneously. All the data were fitted to a novel integrated kinetic-dynamic model. Plasma concentrations of atropine and the amounts of atropine and its primary metabolite, tropine, excreted in the urine were measured by a sensitive gas chromatographic-mass spectrometric assay. The kinetics of elimination of atropine was first order. There was evidence that the kinetics of distribution of the drug was dose dependent. Two phases with apparent half-lives of 1 and 140 min were distinguishable in accordance with a linear two-compartment disposition model for atropine. The urinary excretion of unchanged drug was 57% of the dose. The steady-state volume of distribution was 210 L, implying extensive tissue binding and/or partitioning. Renal plasma clearance was 660 mL/min, suggesting significant tubular secretion. The renal clearance of atropine depended on urine flow. Urinary excretion of tropine amounted to 29% of the dose. The kinetics of the metabolite was first order.