EFFECTS OF BOLUS ADMINISTRATION OF ORG-9426 IN CHILDREN DURING NITROUS-OXIDE HALOTHANE ANESTHESIA

ORG-9426 is a new steroidal nondepolarizing neuromuscular blocking drug. We determined the dose-response relationship of ORG-9426 in 62 children (aged 1-5 yr) during nitrous oxide-halothane anesthesia by means of log-probit transformation and least-squares linear regression of the initial dose and response. Twelve additional patients received a bolus of 600-mu-g/kg (2 X the dose estimated to produce 95% depression of neuromuscular function [ED95]) of ORG-9426. Neuromuscular blockade was monitored by recording the electromyographic activity of the adductor pollicis muscle resulting from supramaximal stimulation of the ulnar nerve at 2 Hz for 2 s at 10-s intervals. To determine the dose-response relationship, patients randomly received initial bolus doses of 120 (n = 15), 160 (n = 16), 200 (n = 16), or 240 (n = 15) ug/kg ORG-9426. The resulting dose estimated to produce 50% depression of neuromuscular function (ED50) and ED95 were 179 and 303-mu-g/kg, respectively. Time from administration of 600-mu-g/kg to onset of 90% and 100% neuromuscular block was 0.8 t 0.1 (0.5-1.3) and 1.3 +/- 0.2 (0.7-2.8) min. The time to recovery of neuromuscular transmission to 25% (T25) was 26.7 +/- 1.9 (17.2-39.0) min. The recovery index (T25-75) was 11.0 +/- 1.6 (6.0-22.8) min, and the time to complete recovery of the magnitude of the fourth response to a train-of-four stimuli divided by the magnitude of the first response (T4/T1) greater-than-or-equal-to 0.75 was 41.9 +/- 3.2 (26.5-57.7) min. The heart rate transiently increased from 90 +/- 4 (68-108) to 106 +/- 4 (76-122) beats/min (P < 0.01) within 1 min after ORG-9426 (2 X ED95) administration. The relatively rapid onset of action of a bolus of ORG-9426 that can produce paralysis and the minimal change in heart rate make this neuromuscular blocking drug useful in children in situations where rapid tracheal intubation is desired.