Relative potency of vecuronium in male and female patients in Britain and Australia

We compared the potency of vecuronium when given to similar patients in Brisbane, Australia, and Cardiff, United Kingdom. Forty patients in each centre were anaesthetized using the same technique with propofol, fentanyl, nitrous oxide and vecuronium either 20 or 30 μg kg −1 by random allocation. Neuromuscular block was measured with similar Datex Relaxographs. There was no significant difference in potency between British and Australian patients. The ED 50 , and ED 95 for a British male of average weight were 29.5 μg kg −1 (95% confidence limits 27.3–32.3 μg kg −1 ) and 51.3 μg kg −1 (44.3–63.9 μg kg −1 ), respectively. ED 50 and ED 95 for Australians were 5.5% greater, with confidence limits from 4% less to 17% greater. Females were significantly more sensitive to vecuronium than males, requiring 22% less drug to achieve the same degree of neuromuscular block (confidence limits 12–32%). The results are consistent with the ED 50 being independent of body weight when the dose is expressed as μg kg −2/3 , but not as μg or μg kg −