The clinical pharmacology of doxacurium in young adults and in elderly patients.

Neuromuscular blockade induced by doxacurium 30 micrograms.kg-1 was compared in 21 young (18-55 years) and 17 elderly (65-85 years) patients. Anaesthesia was induced with thiopentone and maintained with fentanyl, nitrous oxide in oxygen and isoflurane. Neuromuscular blockade was measured electromyographically (Datex Relaxograph) at the adductor pollicis using train-of-four stimuli at 20 s intervals. The depth of maximum neuromuscular blockade was similar in young and elderly patients (median 100% compared to 96%). However, the onset was significantly slower in the elderly: their mean (SD) time to 90% suppression of the first response of the train-of-four was 7.7 (1.8) min compared to 5.7 (1.7) min in the young (p = 0.002). Four min after doxacurium, the conditions for tracheal intubation were significantly poorer in the elderly (p < 0.001). Mean (SD) recovery of first response of the train-of-four to 25% of control was unaffected by age: young 79.0 (41.6) min; elderly 66.2 (32.1) min (p > 0.05). When the first response had reached 25% of control, neuromuscular blockade was antagonised with neostigmine 60 micrograms.kg-1. The mean time to first response to 90% of control was similar in the young and the elderly patients (9.1 min compared to 10.4 min). Recovery of the train-of-four ratio to 0.7 was significantly slower in the elderly: mean (SD) 17.1 (10.6) min compared to 10.1 (7.0) min (p = 0.03). Doxacurium was associated with clinically insignificant haemodynamic changes in both groups.