The potency (ED50) and cardiovascular effects of rapacuronium (Org 9487) during narcotic-nitrous oxide-propofol anesthesia in neonates, infants, and children

We studied the neuromuscular blocking effects of rapacuronium (Org 9487) (d ose-response curve, onset, and 50% effective dose [ED50] value), and change s in heart rate and blood pressure, as well as evidence of histamine releas e in neonates, infants, and children in an open-label, randomized, two-cent er study. Fifteen neonates, 30 infants, and 30 children were studied. Anest hesia was induced and maintained with propofol, nitrous oxide:oxygen (60:40 ), and fentanyl. Mechanomyographic monitoring of neuromuscular function was performed at the thumb. The potency (ED50) for neonates, infants, and chil dren were 0.32 (95% confidence interval [CT] 0.15-0.61), 0.28 (95% CI 0.11- 0.61), and 0.39 (95% CI 0.17-0.85) mg/kg, respectively. Neonates who receiv ed 0.3, 0.6, or 0.9 mg/kg Org 9487 developed a maximum T-1 twitch depressio n of 34 +/- 28%, 98 +/- 3%, and 99 +/- 2%, respectively. Time-to-peak effec t (onset time) for 0.9 mg/kg Org 9487 was 57 +/- 20 s. Maximum percent T-1 twitch depression (+/-SD) in infants who received 0.3, 0.6, or 0.9 mg/kg ra pacuronium was 41 +/- 34%, 96 +/- 7%, and 100 +/- 1%, respectively. Time-to -peak effect for 0.9 mg/kg Org 9487 was 62 +/- 29 s. In children 03, 0.6, a nd 0.9 mg/kg rapacuronium resulted in an average percent T-1 twitch suppres sion of 29 +/- 23, 83 +/- 11, and 90 +/- 16, respectively. Time-to-peak eff ect of 0.9 mg/kg Org 9387 was 96 +/- 33 s, respectively. There was no evide nce of histamine release or significant changes in heart rate or blood pres sure in either group at any dose. Rapacuronium is a low-potency nondepolari zing muscle relaxant with a fast onset of relaxation and minimal cardiovasc ular effects. Its potency (ED50) is similar in neonates (0.32 mg/kg), infan ts (0.28 mg/kg), and children (0.39 mg/kg). T-1 suppression (90% +/- 16) is less and time to peak effect (96 +/- 33 s) is greater (0.9 mg/kg rapacuron ium) in children, compared with the combined group of infants and neonates. Implications: This study assesses the potency of rapacuronium (Org 9487) i n pediatric patients. The potency of rapacuronium is similar in neonates (0 .32 mg/kg), infants (0.28 mg/kg), and children (0.39 mg/kg).