Dose-response relationships for neostigmine antagonism of vecuronium-induced neuromuscular block in adults and the elderly.

We have studied the dose-response relationship for neostigmine in 36 adult (ages 18-50 yr) and 36 elderly (ages > 70 yr) subjects during antagonism of neuromuscular block induced by vecuronium. All patients received vecuronium 0.08 mg kg-1 and neuromuscular block was monitored mechanomyo-graphically using the train-of-four (TOF) mode of stimulation. Six patients of each age group were allocated randomly to receive neostigmine 5, 15, 25, 35 or 45 micrograms kg-1 or saline at 10% recovery of T1 (first response in the TOF). TOF ratios were recorded continuously over the next 10 min and the values at 1-min intervals from 5 min onwards were used to construct the dose-response relationships. There was a significant difference (P < 0.05) in the time to spontaneous recovery of T1 to 10% between the adults (24 (SD 5.5) min) and the elderly (33 (7.8) min). Dose-response curves for neostigmine were parallel in the two age groups, but those for the elderly were significantly to the right of the curves for the adults. This suggests an apparently lesser relative potency of neostigmine, or the requirement of a larger dose, in the elderly for attaining antagonism of a moderately intense vecuronium block at the same time as in adults.