PHARMACODYNAMIC BEHAVIOR OF ROCURONIUM IN THE ELDERLY

This study compared the potency and time course of action of rocuronium (ORG 9426) in elderly and young patients during nitrous oxide-opioid anaesthesia. One hundred ASA physical status I-II patients (60, aged 65-80 yr, and 40, aged 20-45 yr) were studied by measuring the force of contraction of the adductor pollicis in response to train-of-four stimulation of the ulnar nerve. After induction of anaesthesia with thiopentone and maintenance with N2O/O2 and fentanyl, rocuronium 120, 160, 200, or 240 mug . kg-1 was administered to determine dose-response curves. When maximum block had been obtained, further rocuronium to a total of 300 mug . kg-1 was given. Additional doses of 100 mug . kg-1 were administered when the first twitch height (T1) had recovered to 25% control. At the end of surgery neuromuscular blockade was allowed, whenever possible, to recover spontaneously until T1 was 90% of control before administration of neostigmine. There was no difference in the potency of rocuronium in the elderly and the younger patients. The ED50 was 196 +/- 8 (SEE for the mean) in elderly, vs 215 +/- 17 mug . kg-1 in young patients (NS). When individual cumulative dose-response curves were constructed, the ED50 was 203 +/- 7 (SEM) and 201 +/- 10 mug . kg-1 in the elderly and the young respectively (NS). However, the onset of maximum neuromuscular block was slower in the elderly 3.7 +/- 1.1 (SD) vs 3.1 +/- 0.9 min, P < 0.05). The time to 25% T1 recovery was longer in the elderly (11.8 +/- 8.1 vs 8.0 +/- 6.5 min, P < 0.05) as was the recovery index, time from 25 to 75% T1 recovery (15.5 +/- 6.2 vs 11.2 +/- 4.9 min, P < 0.05). The duration of neuromuscular block after each maintenance dose was longer in the elderly (P < 0.01) and increased gradually with time. It is concluded that rocuronium is an intermediate-acting neuromuscular blocking drug with a similar potency in elderly and young patients, but the onset and recovery of neuromuscluar blockade are slower in the elderly.