BACKGROUND: Currently no information is available about the effective dose (ED) of rocuronium in Koreans. The purpose of this study was to determine the ED of rocuronium in a Korean cohort.

METHODS: We studied one hundred and twenty patients with a class I or II ASA physical status. Anesthesia was induced with propofol 2 mg/kg and fentanyl 2µg/kg intravenously, and maintained by the continuous infusion of propofol 5 mg/kg/h and 100% oxygen by mask ventilation. Additional increments of fentanyl 50µg were given as required, and surface electrodes were applied over the ulnar nerve at the wrist. Before each dose of rocuronium was administered intravenously, all patients were stimulated with a 50 Hz supramaximal tetanic stimulation for 5 seconds followed by a 1 Hz single twitch stimulation for 5 minutes to stabilize muscle contraction. The control value was then calibrated by acceleromyography. Twenty female patients were cumulatively administered rocuronium, at an initial dose of 100µg/kg followed by doses incremented by 50µg/kg. And 100 patients were allocated to five single dose groups. Subjects these dose groups were randomly administered 100µg/kg, 150µg/kg, 200µg/kg, 250µg/ kg, or 300µg/kg of rocuronium. We recorded both the 0.1 Hz single twitch responses of the adductor pollicis and the onset times to maximal blockade. The effect of rocuronium on single twitch was calculated as % reduction versus the control. Results were expressed as means ± SD or as 95% confidence intervals. A P value of < 0.05 was considered statistically significant. EDs were estimated by linear regression analysis using a probit model.

RESULTS: No significant differences were found in age, weight, height, or temperature among the dose groups. ED₅₀ and ED₉₅ were determined to be 184µg/kg and 382µg/kg, respectively. For men, ED₅₀ and ED₉₅ were 188µg/kg, 386µg/kg and for women, 180µg /kg, 376µg/kg, respectively. The ED₅₀ and ED₉₅ as determined by the cumulative method in women were 212µg/kg, 445µg/kg, respectively. As the dose of rocuronium increased, onset times decreased. Mean onset time was 178 sec.

CONCLUSIONS: The mean ED₉₅ of rocuronium in Koreans was determined to be 382µg /kg, and the ED of women was lower than that of men. The dose-response curve of the cumulative method was positioned to the right of that of the single bolus method in women. The onset time to maximum blockade reduced as the dose was increased.