The interaction of diazepam with vecuronium: a clinical study

Diazepam, known to possess myorelaxation property, has been widely used clinically to control muscular rigidity and spasticity. The interactions of diazepam with neuromuscular blocking agents have been extensively studied, yet the results reported are somewhat controversial and inconclusive.

The interaction of diazepam with one of the neuromuscular blocking agents, vecuronium, was studied in 20 ASA I-II patients undergoing elective surgery. They were randomly assigned to two groups with ten in each group. Anesthesia was induced with fentanyl, thiopental and vecuronium and maintained with 1% halothane and 70% N2O in O2. The experimental group received diazepam (0.2 mg/kg) 3 minutes prior to vecuronium (0.1 mg/kg) during induction while the control group received vecuronium (0.1 mg/kg) straight without diazepam. Control records of the integrated electromyography showed the response to train-of-four supramaximal stimulation by a Datex Relaxograph during induction. In no time when the first twitch (T1) recovered to 25% of the control, it was topped up again with another intraoperative dose of vecuronium (0.025 mg/kg). From the derived data, the following parameters were calculated and analysed: (1) onset time T10 (the time from the end of injection of vecuronium during induction to depression of T1 to 10% of control twitch height); (2) duration time T25 (the time from administering vecuronium during induction to the time when T1 recovered to 25% of the original twitch height); (3) topup time T25-25 (the time from administering the top dose of vecuronium to the time when T1 returned to 25% of control twitch height again) and (4) recovery time T25-50 (the time of recovery of T1 from 25% to 50% of the control twitch height at the end of the operation).

Significant differences between both groups were found in T10 (221.8 +/- 62.2 vs 135.4 +/- 23.3 sec, p < 0.01) and T25 (41.9 +/- 10.2 vs 50.6 +/- 9.4 min, p < 0.05). The results of T25-25 and T25-50 did not differ much (26.6 +/- 6.9 vs 29.3 +/- 4.4 min, p > 0.05 and 15.0 +/- 8.9 vs 16.9 +/- 8.7 min, p > 0.05 respectively).

The administration of diazepam (0.2 mg/kg) three minutes prior to vecuronium (0.1 mg/kg) during induction may hasten the onset of vecuronium and prolong its duration of action.