The Potency (ED50) and Cardiovascular Effects of Rapacuronium (Org 9487) During Narcotic-Nitrous Oxide-Propofol Anesthesia in Neonates, Infants, and Children


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Abstract

We studied the neuromuscular blocking effects of rapacuronium (Org 9487) (dose-response curve, onset, and 50% effective dose [ED50] value), and changes in heart rate and blood pressure, as well as evidence of histamine release in neonates, infants, and children in an open-label, randomized, two-center study. Fifteen neonates, 30 infants, and 30 children were studied. Anesthesia 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 children were 0.32 (95% confidence interval [CI] 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 received 0.3, 0.6, or 0.9 mg/kg Org 9487 developed a maximum T1 twitch depression of 34 ± 28%, 98 ± 3%, and 99 ± 2%, respectively. Time-to-peak effect (onset time) for 0.9 mg/kg Org 9487 was 57 ± 20 s. Maximum percent T1 twitch depression (±SD) in infants who received 0.3, 0.6, or 0.9 mg/kg rapacuronium 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 0.3, 0.6, and 0.9 mg/kg rapacuronium resulted in an average percent T1 twitch suppression of 29 ± 23, 83 ± 11, and 90 ± 16, respectively. Time-to-peak effect of 0.9 mg/kg Org 9487 was 96 ± 33 s, respectively. There was no evidence of histamine release or significant changes in heart rate or blood pressure in either group at any dose. Rapacuronium is a low-potency nondepolarizing muscle relaxant with a fast onset of relaxation and minimal cardiovascular effects. Its potency (ED50) is similar in neonates (0.32 mg/kg), infants (0.28 mg/kg), and children (0.39 mg/kg). T1 suppression (90% ± 16) is less and time to peak effect (96 ± 33 s) is greater (0.9 mg/kg rapacuronium) in children, compared with the combined group of infants and neonates.ImplicationsThis study assesses the potency of rapacuronium (Org 9487) in 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).

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