Rocuronium-induced neuromuscular blockade is affected by chronic phenytointherapy

Patients receiving chronic anticonvulsant therapy have been reported to sho w resistance to certain nondepolarizing neuromuscular blockers. In this stu dy, the effects of chronic phenytoin therapy on the onset, duration, and re covery of rocuronium action was assessed. Thirty-six patients scheduled for various neurosurgical procedures were studied: 18 receiving chronic phenyt oin therapy (Group I) and 18 controls (Group II). Rocuronium 0.6 mg/kg (2 x DE95) was administered after induction of general anesthesia with 4-6 mg/k g thiopental sodium and 3-5 mug/kg intravenous (IV) fentanyl. Maintenance a nesthesia consisted of N2O in O-2, 0.5% end-tidal isoflurane, and a fentany l infusion. Neuromuscular block was monitored with acceleromyography of the adductor pollicis-brevis muscle by using a TOF-GUARD Biometer monitor (Bio meter International A/S. Odense, Denmark). According to the amplitude of th e first response of train-of-four, neither the lag time nor the onset time differed between the two groups. However, the recovery index was significan tly shorter in patients chronically treated with phenytoin (mean recovery i ndex: control group. 8.3 +/- 1.7 minutes: phenytoin group. 6.7 +/- 2.3 minu tes: P <.05). In addition, the times of recovery to 10%, 25%. 75%, and 90% of the baseline response were also significantly shorter in the phenytoin g roup than in the control group. We conclude that the duration of action of rocuronium and the recovery index were affected by chronic phenytoin therap y.