The effect of a muscle relaxant may differ in the elderly for pharmacokinetic and pharmacodynamic reasons. Rocuronium, a derivative of vecuronium is a non depolarizing neuromuscular blocker with a rapid onset and intermediate duration. The purpose of this study was to compare differences in the onset and duration of rocuronium in young adults and the elderly.

The study was approved by our instituitional review board, and informed consent was obtained from all patients. Twenty two young adults (15 59 yr) and 21 elderly (65 80 yr) patients, ASA physical status 1 2 underwent elective orthopedic surgery under general anesthesia. All were anesthetized with pentothal sodium, nitrous oxide, and isoflurane. Rocuronium (0.6 mg/kg) was given and then intubation was performed after TOF response had totally disappeared. Neuromuscular relaxation was measured by TOF response at the adductor pollicis muscle after a supramaximal stimulation of Train-of-four (TOF, 2 Hz every 12 sec) at the ulnar nerve. Onset (disappearance of T1) and the recovery times of T1, T2, T3 and T4 were recorded.

The onset of neuromuscular block was slower in the elderly than the young adults (P < 0.05), and recovery times of T1, T2, T3, and T4 were prolonged in the elderly (P < 0.05).

Rocuronium has a slower onset time and a delayed recovery in the elderly.