Pharmacokinetics and pharmacodynamics of vecuronium administered by bolus and infusion during halothane or balanced anesthesia.

Vecuronium was administered to two patient groups as a single intravenous dose, 60 micrograms/kg, combined with an infusion, 1 microgram/min/kg. Anesthesia was maintained for the first group with a halothane-nitrous oxide technique; the second group received fentanyl-barbiturate-tranquilizer-nitrous oxide. As the infusion ended, plasma vecuronium concentrations were 0.34 (+/- 0.10) microgram/ml for the halothane group and 0.32 (+/- 0.07) microgram/ml for the fentanyl group, associated with 93% (+/- 8) and 88% (+/- 10) twitch depression, respectively. Vecuronium plasma concentration-time data were combined with the simultaneous intensities of neuromuscular blockade to model the kinetic-dynamic values for each patient. For the halothane group the steady-state volume was 0.21 (+/- 0.04) L/kg, the clearance was 2.9 (+/- 0.1) ml/min/kg, and the elimination half-life was 100 (+/- 36) minutes; for the fentanyl group these were 0.20 (+/- 0.08) L/kg, 3.2 (+/- 0.1) ml/min/kg, and 84 (+/- 43) minutes, respectively. Plasma concentrations associated with 50% blockade averaged 0.2 microgram/ml for both groups. Neither the pharmacokinetics nor the pharmacodynamics of vecuronium in humans differed between these two patient groups.