Dose-response curve and time-course of effect of vecuronium in male and female patients

To determine the differences between men and women in the dose-response curve and the time-course of effect of vecuronium, we studied 60 adult patients (30 male and 30 female), ASA I, age 18-51 yr, undergoing elective plastic surgery. Anaesthesia was maintained with nitrous oxide 60% in oxygen; thiopentone and incremental doses of fentanyl were given as required. Neuromuscular function was assessed mechano-myographically using the train-of-four (TOF) stimulation at the wrist every 12 s. The percentage depression of T-1 was used as the study variable. The dose-response relationship of vecuronium was determined by a cumulative dose-response technique. The dose-response curve in men was shifted in a parallel fashion to the right, indicating a decrease in the sensitivity to vecuronium-induced neuromuscular block, compared with women. The ED50, ED90 and ED95 of vecuronium were 23.9 (4.7), 45.4 (11.2) and 55.7 (14.3) mu g kg(-1) in men and 18.4 (3.7), 33.5 (7.8) and 39.8 (9.6) mu g kg(-1) in women respectively. There were statistically significant differences in these values between the two groups (P < 0.01 in each instance). After a total dose of vecuronium 80 mu g kg(-1), neuromuscular block was significantly longer in women than in men. The duration of peak effect, clinical duration, and the total duration were 18.7 (7.1), 26.6 (8.8) and 50.6 (16.0) min respectively in men and 26.0 (7.2), 37.1 (11.2) and 65.9 (20.7) min in women. They differed significantly between men and women (P < 0.005 in each case).