The Effect of Anticonvulsant Therapy on Two Doses of Rocuronium-Induced Neuromuscular Blockade

Larger and more frequent doses of steroidal neuromuscular blocking agents are required to paralyze patients taking anticonvulsants (carbamazepine and phenytoin). We compared the effects of rocuronium on onset, duration, and speed of recovery from neuromuscular blockade (NMB) in anticonvulsant-treated (Tx) and untreated (C or control) patients. Thirty-eight neurosurgical patients were enrolled: 11 Tx and 8 C patients received 0.6 mg/kg rocuronium; 9 Tx and 10 C patients received 1.2 mg/kg rocuronium. Anesthesia was induced with midazolam, fentanyl, and thiopental, and maintained with N2O and isoflurane in O2. The evoked compound electromyograph (EMG) of the hypothenar eminence was recorded (train-of-four supramaximal stimulus at 2 Hz every 20 seconds). Rocuronium was administered after baseline EMG was recorded. Data = mean +/- SD. Rocuronium 1.2 mg/kg significantly shortened onset time [depression of baseline height of first twitch (T1) to 10% of baseline] of NMB versus rocuronium 0.6 mg/kg in both Tx (2.5+/-2 versus 3.3+/-2 minutes) and C (1.3+/-1 versus 2.8+/-1 minute) patients. Duration (recovery to 25% of T1) of NMB was significantly shorter in the Tx patients than in the C patients who received rocuronium 0.6 mg/kg (21+/-9 versus 45+/-20 minutes), but similar in Tx and C patients who received 1.2 mg/kg rocuronium (56+/-24 versus 69+/-21 minutes). The speed of recovery (time from 10 to 25% recovery of T1) was significantly slower in Tx patients who received 1.2 mg/kg rocuronium (9+/-5 minutes) than in those who received 0.6 mg/kg (5+/-3 minutes) and not different from controls who received 0.6 (9+/-4 minutes) or 1.2 mg/kg (12+/-7 minutes) rocuronium. We recommend the use of rocuronium 1.2 mg/kg and very frequent monitoring of NMB in anticonvulsant-treated patients to avoid premature and extremely rapid recovery after the standard 0.6 mg/kg rocuronium.