Pancuronium and vecuronium pharmacokinetics and pharmacodynamics in younger and elderly adults

To evaluate the effect of aging on the distribution, metabolism, and neuromuscular junction sensitivity to pancuronium and vecuronium, the authors determined the pharmacokinetics and pharmacodynamics of these drugs in 12 healthy elderly subjects (70-84 yr) and 12 young adults (30-57 yr) during halothane-nitrous oxide anesthesia. Plasma concentrations of the muscle relaxants were determined using a selective ion-monitoring mass spectrometric technique specific for the parent compound. For vecuronium, plasma clearance (3.7 +/- 1.0 and 5.2 +/- 0.8 ml X kg-1 X min-1, respectively), and volume of distribution at steady-state (179 +/- 31 and 244 +/- 38 ml X kg-1, respectively) were lower in the elderly than in young adults; values for distribution half-lives, elimination half-life, and sensitivity of the neuromuscular junction were similar for the two groups. For pancuronium, there were no statistically significant differences between groups for these pharmacokinetic or pharmacodynamic parameters. However, there was a trend toward reduced clearance (20%) and prolonged elimination half-life (16%) in the elderly as compared to the younger patients. The authors conclude that healthy elective surgical patients between the ages of 70 and 84 yr of age do not differ markedly from younger adults in their pharmacokinetic/pharmacodynamic response to vecuronium and pancuronium.