Duration of the pharmacodynamic interaction between pancuronium and mivacurium.

The aim of this study was to determine for how long the duration of action of increments of mivacurium can be influenced by previous pancuronium administration. Fifteen patients, ASA I or II, undergoing general anaesthesia for major abdominal surgery were investigated. The post-tetanic count (PTC) was measured at the adductor pollicis muscle. Pancuronium 0.1 mg kg-1 was injected first. At recovery of the 10th response of the PTC (PTC10), a second dose of pancuronium was injected (0.02 mg kg-1). On recovery to PTC10, a bolus of mivacurium (0.04 mg kg-1) was given and regularly repeated at recovery of PTC10 until the end of surgery. The mean duration of the second dose of pancuronium was 53 min (SD 13 min) and of the first dose of mivacurium, 66 min (SD 14 min) (P < 0.01). The duration of action of further mivacurium boluses decreased significantly until the fifth dose. It took 222 minutes (95% confidence interval 190, 253 min) after the second pancuronium dose before the duration of action of mivacurium returned to normal values and became constant and predictable.