PHARMACODYNAMICS AND PHARMACOKINETICS OF INTRAMUSCULAR DEXMEDETOMIDINE

The pharmacodynamics and pharmacokinetics of intramuscular dexmedetomidine-a novel alpha2-adrenergic receptor agonist under development for preanesthetic use-were studied in healthy male volunteers. Single intramuscular doses of dexmedetomidine (0.5, 1.0, and 1.5 mug/kg) and placebo were administered to six subjects in a single-blind, multiple crossover study. Dexmedetomidine induced dose-related impairment of vigilance assessed both objectively and subjectively. The drug also caused moderate decreases in blood pressure and heart rate. Plasma norepinephrine was dose-dependently (maximum 89%) decreased. The intramuscular doses resulted in linearly dose-related plasma concentrations of dexmedetomidine. Pharmacokinetic calculations revealed a time to maximum concentration from 1.6 to 1.7 hours, an elimination half-life of 1.6 to 2.4 hours, an apparent total plasma clearance of 0.7 to 0.9 L/hr/kg, and apparent volume of distribution of 2.1 to 2.6 L/kg. The sedative effect of dexmedetomidine dissipated during the 6-hour observation time, but all other effects were still evident 6 hours after administration of the higher doses, paralleling the plasma concentration curves. The relationship of plasma concentrations of dexmedetomidine to pharmacodynamic variables was consistent with a linear pharmacodynamic model. The pharmacodynamic-pharmacokinetic profile of intramuscular dexmedetomidine may be suited to the proposed preanesthetic clinical use of this alpha2-agonist.