BACKGROUND: Atracurium is non-depolarizing neuromuscular blocking agent with intermediate duration of action. The purpose of this study is to determine the effective dose (ED) of atracurium in Korean adults.

METHODS: We studied 100 patients, aged 18-59 yr, who had given informed consent and belonged to class I or II of ASA physical status. We excluded patients who had cardiac, pulmonary, renal, hepatic, neurological, psychiatric, muscular, inflammatory or endocrine disease, as were pregnant women and patient with recent exposure (< 72 hr) to medications known to interfere with neuromuscular transmission. In all patients, anesthesia was induced with intravenous propofol 2 mg/kg and fentanyl 2µg/kg. Anesthesia was maintained with continous infusion of propofol 5 mg/kg and 100% oxygen through mask, supplemented with fentanyl as required. The electrodes were applied over the ulnar nerve at the wrist. Then, the patients were stimulated with a 50 Hz supramaximal tetanic stimulation for 4 seconds and a 1 Hz single twitch for 5 minutes to stablize muscle contraction and then a control value was obtained with acceleromyography (TOF-Guard^®, Organon Technika BV , Netherland). Thereafter, a 0.1 Hz single twitch of adductor pollicis was kept during the study. The 100 patients were randomly divided to five groups. The patients in each group received 90µg/kg, 120µg/kg, 150µg/kg, 180µg/kg, 210µg/kg of atracurium. We measured the maximal response (% reduction) and time to achieve maximal blockade of single twitch. Values were expressed as mean ± SD or 95% confidence intervals. ED values were obtained from the regression analysis using probit model. A P value of < 0.05 was considered statistically significant.

RESULTS: There were no significant defferences in age, body mass index and temperature among dose groups. ED50 and ED95 of atracurium were 128µg/kg, 236µg/kg, respectively. For men, ED₅₀ and ED₉₅ were 127µg/kg, 249µg/kg, respectively. For women, ED₅₀ and ED₉₅ were 128µg/kg, 236µg/kg, respectively. The onset time to maximum blockade was reduced as dose was increased.

CONCLUSIONS: ED₅₀ and ED₉₅ of atracurium in Korean adults were 128µg/kg, 236µg/kg, respectively. There was no difference between the effective doses of men and women. Onset time of atracurium was reduced as doses were increased.