Vecuronium is more potent in Montreal than in Paris

This study was undertaken to compare the potency of vecuronium in patients anaesthetized in Montreal or Paris. Anaesthesia was induced with thiopentone and maintained with N2O, and intermittent boluses of thiopentone and fentanyl in 18 patients in Paris and 19 in Montreal. Neuromuscular blockade was measured using train-of-four stimulation of the ulnar nerve. The force of contraction of the adductor pollicis muscle was measured. Single doses of vecuronium, 20, 30, or 40 micrograms.kg-1 were given by random allocation. Dose response curves were constructed by obtaining the linear regression of the logit of the first response (T1) neuromuscular blockade versus log dose. The patients in Paris required 27% more vecuronium (95% confidence limits 5-53%; P = 0.01) for the same intensity of blockade. In Montreal, the ED50 and ED90 (+/- SEE for the mean) values were 26.0 +/- 1.4 and 44.2 +/- 2.5 micrograms.kg-1 compared with 33.0 +/- 3.3 and 71.9 +/- 7.2 micrograms.kg-1 in Paris respectively. The patients were comparable with respect to age, sex, height and weight. These results confirm, for vecuronium, the transatlantic difference in potency of neuromuscular blocking drugs which was previously observed with d-tubocurarine between London and New York.