Mivacurium when preceded by pancuronium becomes a long-acting muscle relaxant

To ensure rapid recovery of neuromuscular block, it might be useful to administer a short-acting relaxant after a long-acting one. Therefore, the interaction between pancuronium and mivacurium was investigated when mivacurium was administered during the recovery from pancuronium block.

After written informed consent, 41 adult patients were studied during propofol/alfentanil/nitrous oxide/oxygen anesthesia. Neuromuscular function was monitored using an electromyographic (EMG) method. AFter a stable EMG calibration response, cumulative doses of pancuronium were given to establish a 95% neuromuscular block. In the control group, and ED95 dose of 100 microg/kg mivacurium was administered instead of pancuronium. When the EMG response after pancuronium or mivacurium had recovered to 25% of the baseline, a single randomized intravenous bolus dose of 10 or 70 microg/kg mivacurium was given. Thereafter, spontaneous recovery of the neuromuscular function was recorded.

The time from pancuronium until T1 25% EMG recovery was 38 +/- 12 min (mean +/- SD). The respective times after 10 or 70 microg/kg mivacurium were 28 +/- 8 and 54 +/- 7 min in the pancuronium group or 3 +/- 1 (n=3) and 10 +/- 4 min in the mivacurium group (P=0.0001). Times to 95% EMG recovery after 10 or 70 microgm/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 microg/kg mivacurium group, respectively (P<0.0001). Recovery indexes after 10 or 70 microg/kg mivacurium wre 26 +/- 4 and 22 +/- 6 min in the pancuronium group or 7 +/- 3 (n=3) and 5+/- 2 min in the mivacurium group, respectively (P<0.0001). Times from the administration of 10 or 70 microg/kg mivacurium until train-of-four ration 0.7 were 94 +/- 16 and 111 +/- 14 min in the pancuronium group and 12 +/- 4 and 22 +/- 8 min in the mivacurium group, respectively (P<0.0001).

After pancuronium, mivacurium is not a short acting neuromusclar blocking agent.