Fade characteristics and onset times following administration of pancuronium, tubocurarine and a mixture of both agents.

The onset characteristics of pancuronium, tubocurarine and a mixture of these two neuromuscular blocking drugs were studied during the induction of neuromuscular blockade, using a train-of-four pattern of stimulation. Four characteristics of onset were defined: train-of-four fade = a reduction in the height of the fourth twitch greater than a reduction in the height of the first twitch; latent onset time = time from injection of neuromuscular blocker to a greater than 5% reduction in the first twitch in the train-of-four; total onset time = time to 90% reduction in twitch height; manifest onset time = time from 5% to 90% reduction in twitch height. Tubocurarine was associated with significantly more fade than either pancuronium or the mixture. During the period of study the fade profile of the mixture was almost identical to that of pancuronium alone. The mixture had the most rapid total onset time (100.3 s), tubocurarine the slowest (135.1 s) and pancuronium was intermediate (124.0 s). The mixture and tubocurarine had similar latent onset times, while the mixture and pancuronium had similar manifest onset times.