MIVACURIUM WHEN PRECEDED BY PANCURONIUM BECOMES A LONG-ACTING MUSCLE-RELAXANT

Background: To ensure rapid recovery of neuromuscular block, it might be useful to administer a short-acting relaxant after a long-acting on e. Therefore, the interaction between pancuronium and mivacurium was i nvestigated when mivacurium was administered during the recovery from pancuronium block. Methods: After written informed consent, 41 adult p atients were studied during propofol/alfentanil/nitrous oxide/oxygen a nesthesia. Neuromuscular function was monitored using an electromyogra phic (EMG) method. After a stable EMG calibration response, cumulative doses of pancuronium were given to establish a 95% neuromuscular bloc k. In the control group, an ED(95) dose of 100 mu g/kg mivacurium was administered instead of pancuronium. When the EMG response after pancu ronium or mivacurium had recovered to 25% of the baseline, a single ra ndomized Intravenous bolus dose of 10 or 70 mu g/ kg mivacurium was gi ven. Thereafter, spontaneous recovery of the neuromuscular function wa s recorded. Results: The time from pancuronium until T1 25% EMG recove ry was 38 +/- 12 min (mean +/- SD). The respective times after 10 or 7 0 mu g/kg mivacurium were 28 +/- 8 and 54 +/- 7 min in the pancuronium group of 3 +/- 1 (n = 3) and 10 +/- 4 min in the mivacurium group (P = 0.0001). Times to 95% EMG recovery after 10 or 70 mu g/kg mivacurium were 77 +/- 14 and 97 +/- 16 min in the pancuronium group and 11 +/- 3 and 20 +/- 7 min in the mivacurium group, respectively (P < 0.0001). Recovery indexes after 10 or 70 mu g/kg mivacurium were 26 +/- 4 and 22 +/- 6 min in the pancuronium group or 7 +/- 3 (n = 3) and 5 +/- 2 m in in the mivacurium group, respectively (P < 0.0001). Times from the administration of 10 or 70 mu g/kg mivacurium until train-of-four rati o 0.7 were 94 +/- 16 and 111 +/- 14 min in the pancuronium group and 1 2 +/- 8 and 22 +/- 8 min in the mivacurium group, respectively (P < 0. 0001). Conclusions: After pancuronium, mivacurium is not a short-actin g neuromuscular blocking agent.