Pharmacodynamics of mivacurium in infants.

A computerized infusion system was used to determine mivacurium infusion requirements to maintain 95% and 50% neuromuscular block in 15 infants less than 1 yr of age. Neuromuscular block was measured by adductor pollicis EMG and anaesthesia maintained with 66% nitrous oxide in oxygen and alfentanil 50-100 micrograms kg-1 h-1. Neuromuscular block was produced by repeated bolus doses of mivacurium 0.1 mg kg-1; subsequently the target neuromuscular block was maintained by a closed loop infusion. Dose potency of mivacurium was similar to that previously published in children with a similar anaesthetic technique. Mean mivacurium requirement for 95% neuromuscular block was 820 (SD 300) micrograms kg-1 h-1, which represented an hourly requirement of 6.6 (1.5) individual ED95 doses. Infusion requirement for 50% neuromuscular block was 320 (150) micrograms kg-1 h-1. These infusion rates were similar to those in children. No side effects of mivacurium were noticed.