Pharmacokinetics and pharmacodynamics of vecuronium bromide.

The pharmacokinetics and pharmacodynamics of vecuronium bromide were studied in patients under general anesthesia of enflurane and nitrous oxide in oxygen. Eighteen patients were randomly divided into two groups which received either 0.05 mg.kg(-1) (low dose group) or 0.20 mg.kg(-1) (high dose group) of vecuronium intravenously. The plasma concentration of vecuronium was determined by high performance liquid chromatography. The neuromuscular blocking effect was assessed by measuring the twitch tension of the adductor pollicis muscle elicited by supramaximal electrical stimulation. Pharmacokinetic analysis was carried out using a two compartment model. The relationship between the T4/T1 and T1/ control T1 ratios differed during onset and spontaneous offset of the blockade; the T4/T1 ratios were significantly higher during onset than during offset, although there were large variations of fade in the train-of-four response in each patient during offset. These results suggest that it is difficult to estimate the T1/control T1 ratio by the T4/T1 ratio during offset. Pharmacokinetic analysis revealed that the high dose group had a shorter elimination half-life than did the low dose group. A shorter elimination half-life at a high dose may be to some extent due to hepatic clearance. The pharmacokinetic parameters bore no fixed relationship to the pharmacodynamics in each patient.