Chronic carbamazepine therapy does not influence mivacurium-induced neuromuscular block

Patients receiving anticonvulsant drugs chronically are relatively resistant to some non-depolarizing neuromuscular blocking drugs. We investigated the influence of chronic carbamazepine therapy on neuromuscular block induced by mivacurium in 20 otherwise healthy individuals undergoing neurosurgical operations, 10 of whom were receiving chronic treatment with carbamazepine and the other 10 served as controls. The median duration of carbamazepine therapy was 22 weeks (range 4-182 weeks). After premedication with oral diazepam, anaesthesia was induced with fentanyl and thiopentone and maintained with 0.5% isoflurane and nitrous oxide in oxygen. The ulnar nerve was stimulated and the evoked electromyogram recorded using a Datex NMT monitor. Mivacurium 0.15 mg kg-1 (2 x ED95) was given as a bolus i.v. Based on the response to the first of four stimuli, lag time, onset-time, times to recovery to 10%, 25%, 50% and 75% of baseline responses and recovery index (RI 25-75%) did not differ between the two groups. We conclude that mivacurium-induced neuromuscular block was not influenced by preceding chronic carbamazepine therapy.