Recovery from mivacurium-induced neuromuscular blockade is not affected by anticonvulsant therapy

Long-term chronic anticonvulsant therapy produces a resistance to the effects of all nondepolarizing neuromuscular blocking agents studied to date. Since the metabolism of mivacurium is unique among the nondepolarizing neuromuscular blocking agents, the effect of anticonvulsants on its recovery parameters was examined. Forty five patients were separated into three groups based on the number of chronic anticonvulsant medications the subjects were taking: subjects in group 1, the control group, took no anticonvulsant medication; group 2 subjects took one medication; and group 3 subjects took two medications. Mivacurium, 0.15 mg/kg i.v., was administered after induction of general anesthesia with thiopental sodium, 4-6 mg/kg, and fentanyl 2-4 μg/kg i.v. Maintenance anesthesia consisted of N₂O in O₂, 0.2-0.3% end-tidal isoflurane, and a fentanyl infusion. The evoked compound electromyograph (ECEMG) of the adductor pollicis-brevis muscle was measured for time of onset, T-1 (time at which ECEMG signal reaches 5, 25, 50, and 75% of baseline), TR (TOF ratio), and recovery index. T-1 at 25% was 18.2 ± 1.8, 20.7 ± 1.9, and 21.5 ± 1.4 min for groups 1, 2, and 3, respectively, with TR at 25% being 23.7 ± 2.3, 26.9 ± 2.4, and 27.3 ± 2.3 min. No significant differences were noted in neuromuscular recovery between groups at any time point. These results fail to demonstrate the resistance to the nondepolarizing neuromuscular blockade of mivacurium that hits been observed with other nondepolarizing agents.