Clinical pharmacology of pipecuronium in infants and children during halothane anesthesia

We determined the cumulative dose-response relations of pipecuronium in infants and children during nitrous oxidehalothane anesthesia. 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. Patients were stratified into four groups according to age: 3 mo or older but not yet 6 mo (n = 10), 6 mo or older but not yet 12 mo (n = 10), 1 yr or older but not yet 3 yr (n = 10), and 3 yr or older but not yet 6 yr (n = 9). The mean ED50 of pipecuronium in these age groups was 18, 20, 21, and 24 micrograms/kg, respectively; the mean ED95 was 33, 38, 47, and 49 micrograms/kg, respectively. The ED95 of pipecuronium was statistically significantly less for the 3-6-mo-old patients than for children between 1 and 6 yr of age. Similarly, pipecuronium dosage requirements calculated on the basis of body surface area were significantly less in infants 3-12 mo of age than in children 1-6 yr of age. Thus, compared with children, infants appear to be more sensitive to the neuromuscular blocking effects of pipecuronium. Duration (T25) of action after cumulative dosing with pipecuronium was approximately 20 min in infants and 30 min in children. Spontaneous recovery indices were not prolonged in the younger patients. The average T25-75 recovery index was 27.1 +/- 9.6 min. There were no changes in cardiac rhythm, heart rate, or blood pressure attributable to pipecuronium during this study.