Atracurium-induced neuromuscular block is not affected by chronic anticonvulsant therapy with carbamazepine

Patients on chronic anticonvulsant therapy are relatively resistant to some nondepolarizing neuromuscular blockers. Because of the controversial reports on atracurium, the purpose of the present study was to determine the effect of long-term carbamazepine treatment on the neuromuscular block produced by this muscle relaxant.

Eighteen otherwise healthy individuals scheduled for neurosurgical interventions were studied. Eight patients had received carbamazepine for an average of 41 weeks (range 4-156 weeks) prior to surgery. Ten patients without carbamazepine exposure served as controls. After premedication with oral diazepam, anaesthesia was induced with fentanyl and thiopental and maintained with nitrous oxide and isoflurane in oxygen. Atracurium was given for neuromuscular blockade and the evoked electromyogram (EMG) was recorded with a Datex Monitor NMT.

The lag time, the onset time, the duration 10%, 25%, 50%, 75% and the interval 25-75% did not differ between the groups.

Our results with atracurium differ from previous data demonstrating an influence of carbamazepine therapy on the pharmacokinetics and/or pharmacodynamics of other non-depolarizing muscle relaxants. As documented in this study, atracurium produces adequate neuromuscular block in patients chronically exposed to carbamazepine. Chronic carbamazepine therapy does not influence the onset time and duration of action of atracurium-induced neuromuscular block.