Pharmacodynamic effects of 51W89, an isomer of atracurium, in children during halothane anaesthesia

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Abstract
51W89 is one of the 10 stereoisomers of atracurium with less propensity to release histamine than atracurium. We evaluated dose-response data and neuromuscular effects of 2 × ED95 dose and maintenance doses of 51W89 during halothane anaesthesia in 68 children, 2–12 yr old. Neuromuscular function was monitored by evoked adductor pollicis EMG. Log-probit, single-dose, dose-response data gave ED50 and ED95 values of 23 and 41 μg kg−1, respectively, for 51W89. Twice the ED95 dose (80μgkg−1) had an onset time (time from administration to maximum effect) of 2.5 (SD 0.8) min, a clinical duration (time to 25% EMG recovery) of 31 (7) min and a recovery index (time from 25 to 75% EMG recovery) of 11.1 (1.7) min. Seventy-nine incremental doses of 51W89 of 0.5 × ED95 dose were given in 16 children at 85–90% neuromuscular block. The mean duration of these doses was 13.4 (3) min, with a calculated hourly maintenance requirement of 51W89 of 94 (19) μg kg−1. Duration of effect of incremental doses remained constant within individuals reflecting non-cumulative properties. There were insignificant changes in arterial pressure and heart rate after 51W89 and no side effects were observed. We regard 51W89 as a promising, non-cumulative, intermediate-acting neuromuscular.blocking agent the effects of which can be antagonized easily by neostigmine.

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