Recovery from pancuronium and vecuronium administered simultaneously in the isolated forearm and the effect on recovery following administration after cross-over of drugs.

If recovery of neuromuscular block in the isolated arm is determined by biophase binding, then a significant amount of drug will still be present in the biophase at 50% recovery of twitch response. To test this hypothesis we administered pancuronium at 50% recovery from vecuronium block and vecuronium at 50% recovery from pancuronium block in the isolated forearms of volunteers. To ensure that any effect of drug released into the plasma did not affect the results, both experiments were performed simultaneously, one in each forearm of each volunteer. Control experiments were performed to determine the effect of subsequent injections of the same drug at 50% recovery and of subsequent injections of the alternative drug (i.e., vecuronium following pancuronium and pancuronium following vecuronium) at 100% recovery of the twitch response. Prior administration of vecuronium significantly shortened the recovery from subsequent pancuronium when administered at 50% recovery, but not 100% recovery, and pancuronium significantly increased the recovery rate of vecuronium when given at 50% recovery but not 100% recovery. These findings support the concept of biophase binding of nondepolarizing neuromuscular blocking drugs.