Optimum time for neostigmine administration to antagonize vecuronium-induced neuromuscular blockade

We followed the recovery time course in 46 patients antagonized by neostigmine (0.036 mg kg-1) at different levels of vecuronium-induced neuromuscular blockade ranging from post-tetanic count 1 to train-of-four ratio 0.4 and in 15 patients during spontaneous recovery. Non-linear regression curve fit analyses showed that the optimal time for neostigmine administration was when the first twitch in the train of four (T1) was between 1% and 10%. Visual analyses of the scattergram in which the level of block, when neostigmine was given, was plotted against total recovery time (the time elapsed from administration of the last dose of vecuronium to train-of-four ratio 0.7) gave the same result. The reduction in total recovery time achieved by neostigmine was 32.6 min (SE diff. 6.0 min). To achieve the optimum effect, neostigmine must therefore be given 32.6 min plus the required time for peak effect of neostigmine (5.3-7.1 min), i.e. 37.9-39.7 min, before train-of-four ratio 0.7 is reached. During spontaneous recovery this corresponds to a T1 between 1% and 15%.