THE PHARMACODYNAMICS OF MIVACURIUM PRECEDED BY ATRACURIUM OR CISATRACURIUM IN CHILDREN

We evaluated whether mivacurium maintains its short duration of effect when preceded by atracurium or cisatracurium in 45 children during pr opofol/alfentanil/N2O/O2(2), anesthesia. Neuromuscular response was re corded by using an adductor pollicis electromyogram (EMG). Children we re randomized to receive two doses of atracurium (350 mu g/kg and 70 m u g/kg in Group AM), cisatracurium (64 mu g/kg and 10 mu g/kg in Group CM), or mivacurium (200 mu g/kg and 100 mu g/kg in Group MM), followe d by a final dose of mivacurium 100 mu g/kg. The second and third dose s of the muscle relaxants were administered at 25% EMG recovery. After the final dose of mivacurium, the times to 95% of EMG recovery in gro ups AM, CM, and MM were (median with 10-90 percentile range) 33.0 (28. 0-40.0) min, 30.7 (26.0-40.3) min, and 10.3 (8.0-14.0) min,respectivel y (P < 0.0001). The recovery times to a train-of-four ratio of 0.70 we re 30.3 (24.7-37.0) min, 28.0 (24.7-37.7) min, and 10.3 (8.0-13.7) min for groups AM, CM, and MM, respectively (P < 0.0001). Thus, the durat ion of effect of mivacurium was prolonged by 200% if preceded by eithe r atracurium or cisatracurium. Implications: We compared the pharmacod ynamics of mivacurium given alone or preceded by atracurium or cisatra curium in children. The duration of effects of mivacurium was prolonge d by 200% if preceded by either atracurium or cisatracurium. This impl ies that mivacurium has a short duration of effect only when given as a single relaxant.