Maintenance of surgical muscle relaxation by repeat doses of vecuronium and atracurium at three different dose levels.

The time-course of the neuromuscular effects of vecuronium (n = 25) and atracurium (n = 25) has been compared at three different levels of maintenance dose in anaesthetized patients. Following intubation with vecuronium 0.1 mg kg-1 or atracurium 0.5 mg kg-1, surgical muscle relaxation was maintained by using increments of equipotent maintenance doses equivalent to 0.5, 1.0 and 1.5 x ED95 for each drug. Repeat doses were administered each time the twitch height, depressed by the previous dose, returned to 25% of its control value. The apparent increase in the duration of action, i.e. the difference between the duration of the last and the first maintenance dose, did not reach statistical significance and approximated 3 +/- 2, 6 +/- 4, 11 +/- 5 and 3 +/- 2, 8 +/- 13, 5 +/- 7 min following the low, medium and high maintenance doses of vecuronium and atracurium, respectively.