There is increasing evidence of gender differences in the pharmacokinetics and pharmacodynamics of aminosteroid neuromuscular blocking agents. Compared to males, females are more susceptible, requiring approximately 30% less rocuronium to achieve the same degree of neuromuscular block. However, little information is available whether this difference is applicable to modern benzylisoquinolines (cisatracurium).

In all, 848 patients (423 males, 425 females) undergoing general surgery under total intravenous anaesthesia with muscle relaxation, tracheal intubation and mechanical ventilation were studied. Patients were randomized to receive a single bolus dose of cisatracurium (0.1 mg kg−1, 221 males and 199 females) or rocuronium (0.6 mg kg−1, 202 males and 226 females). The onset time for 95% depression of T1, clinical duration until 25% recovery and recovery index (T1 from 25% to 75%) were determined with an NMT electromyographic module of the Datex-Ohmeda S/5 Anaesthesia Monitor. The data for male and female groups were compared with appropriate statistical tests (unpaired t-test, Mann–Whitney rank sum test and Fisher’s exact test).

In both groups (cisatracurium and rocuronium), males were significantly taller (P < 0.001) and heavier (P < 0.001) than females, but the body mass index was comparable. For rocuronium, the onset time was shorter 91.7 ± 14.3 s vs. 108.0 ± 14.6 s (P < 0.001) and the clinical duration was increased in females 43.3 ± 7.8 min vs. 31.3 ± 5.5 min (P < 0.001). In the cisatracurium group, both onset times (248.9 ± 60.7 s for males vs. 253.4 ± 70.9 s for females) and clinical duration (42.6 ± 6.9 min for males vs. 43.1 ± 6.9 min for females) were similar. The recovery index was identical for males and females in both groups.

Females were more sensitive than males to a single bolus dose of rocuronium. Under the study conditions described, the onset time was shorter and the clinical duration was increased in female patients. This suggests that the routine dose of rocuronium should be reduced in females compared to males. On the contrary, we could demonstrate no gender differences in the onset time or clinical duration of cisatracurium.