Dose-response relations of doxacurium and its reversal with neostigmine in young adults and healthy elderly patients.

Dose-response relationships for doxacurium and neostigmine were established in 24 young (18-40 yr) and 24 elderly (70-85 yr) patients, ASA physical status I or II, anesthetized with thiopental, fentanyl, nitrous oxide, and isoflurane. Mechanomyographic response of the adductor pollicis muscle to the train-of-four stimulation of the ulnar nerve was recorded. Doxacurium (5, 10, 15, or 20 micrograms/kg IV) was administered by random allocation. After maximal blockade, and additional dose, for a total of 30 micrograms/kg, was administered. When first twitch height recovered to 25%, incremental doses of 5 micrograms/kg were administered for maintenance of relaxation. Neostigmine (5, 10, 20, or 40 micrograms/kg) was injected at 25% first twitch recovery, and neuromuscular monitoring was continued for 10 min. The doses of doxacurium (+/- SEM) required to produce a 50%, 90%, and 95% depression of twitch tension in the young patients were, respectively, 13.3 +/- 1.6, 23.6 +/- 2.8, and 28.6 +/- 3.4 micrograms/kg, not statistically different from corresponding values in the elderly, 11.8 +/- 1.3, 21.2 +/- 2.3, and 25.9 +/- 2.9 micrograms/kg, respectively. Time to 25% recovery after 30 micrograms/kg was 80.2 +/- 12.2 min in the young versus 133.0 +/- 17.1 min in the elderly (P less than 0.05). Neostigmine-assisted recovery was not significantly different in both groups. The estimated doses of neostigmine to obtain 70% train-of-four recovery after 10 min were 53.6 +/- 7.5 micrograms/kg in the young and 41.6 +/- 5.8 micrograms/kg in the elderly (P = NS).(ABSTRACT TRUNCATED AT 250 WORDS)