Rocuronium-induced neuromuscular block is affected by chronic carbamazepine therapy

Background: Patients on chronic anticonvulsant drugs are relatively resista nt to certain nondepolarizing neuromuscular blockers such as pancuronium, v ecuronium, pipecuronium, doxacurium, or metocurine, but not resistant to mi vacurium and atracurium, This study investigated the influence of chronic c arbamazepine therapy on the neuromuscular block induced by the new muscle r elaxant rocuronium. Methods: Twenty-two otherwise healthy individuals scheduled for neurosurgic al operations were studied: 11 of them were on chronic treatment with carba mazepine; the others served as control subjects. The median duration of car bamazepine therapy was 9 weeks (range, 4-312 weeks). After premedication wi th Oral diazepam, anesthesia was induced with fentanyl and thiopental and m aintained with nitrous oxide/oxygen and 0.5% inspired isoflurane. Rocuroniu m, 0.6 mg/kg (2 x ED95), was given for intubation. The ulnar nerve was stim ulated, and the evoked electromyogram recorded using a Datex NMT monitor. Results: Based on the response to the first of four stimuli, neither the la g time nor the onset-time differed between the two groups, However, the int ervals of recovery to 10%, 25%, 50%, and 75% of the baseline response and t he recovery index (RI, 25%-75%) were significantly shorter in patients on c hronic carbamazepine therapy. Conclusions: The authors conclude that the duration of the rocuronium-induc ed neuromuscular block is significantly shortened by preceding chronic carb amazepine therapy.