Sensitivity to vecuronium in myasthenia gravis: a dose-response study.

A cumulative dose plus infusion technique and integrated EMG monitoring of the first dorsal interosseous muscle were used to determine the potency of vecuronium in 20 normal patients and in ten patients with myasthenia gravis under thiamylal, N2O, O2, fentanyl anaesthesia. The mean (+/- SEM) values for ED50, ED90, and ED95 in the normal patients were 19 +/- 1, 31 +/- 1 and 36 +/- 2 micrograms.kg-1, respectively. Myasthenic patients showed increased sensitivity to vecuronium, the mean values for ED50, ED90, and ED95 were 10 +/- 2, 17 +/- 2 and 20 +/- 3 micrograms.kg-1, being 50, 55 and 56 per cent of normal, respectively. We did not demonstrate a difference in sensitivity to vecuronium between those myasthenic patients who received pyridostigmine preoperatively and those who did not, nor among those chronically treated with corticosteroids, compared with those who were not.