Comparison of the neuromuscular effects of mivacurium and suxamethonium in infants and children

We compared both the time course of neuromuscular blockade and the cardiovascular side-effects of suxamethonium and mivacurium during halothane and nitrous oxide anaesthesia in infants 2–12 months and children 1–12 years of age. Equipotent doses of mivacurium and suxamethonium were studied; 2.2×ED95 was used in four groups of infants and children, while 3.4×ED95 was used in two groups of children. Onset of neuromuscular block in infants was not significantly faster with suxamethonium than with mivacurium (P=0.2). In all infants given suxamethonium, intubating conditions were excellent, while, in 6/10 infants given mivacurium, intubating conditions were excellent. Onset of complete neuromuscular block in children was significantly faster with suxamethonium, 0.9 min compared with mivacurium, 1.4 min (P×0.05). Increasing the dose of suxamethonium or mivacurium in children to 3.4×ED95 did not change the onset of neuromuscular block. Recovery of neuromuscular transmission to 25% of initial twitch height (T25) in infants and children was significantly faster after suxamethonium than after mivacurium, at 2.5 and 6 min, respectively (P×0.05). In children given 3.4×ED95 of suxamethonium or mivacurium, recovery from neuromuscular block was almost identical with the dose of 2.2×ED95, with spontaneous recovery to T25 prolonged by only 0.5 min. No infant or child had hypotension after the mivacurium bolus dose.