BIOAVAILABILITY OF INTRAMUSCULAR ROCURONIUM IN INFANTS AND CHILDREN

Background: Intramuscular rocuronium, in doses of 1,000 mu g/kg in inf ants and 1,800 mu g/kg in children, produces complete twitch depressio n in 5-6 min. To determine the rare and extent of absorption of rocuro nium after intramuscular administration, blood was sampled at Various intervals after rocuronium administration by both intramuscular and in travenous routes to determine plasma concentrations (Cp) of rocuronium . Methods: Twenty-nine pediatric patients ages 3 months to 5 yr were a nesthetized with N2O and halothane. The trachea a as intubated, ventil ation was controlled, and adductor pollicis twitch tension was measure d. When anesthetic conditions were stable, rocuronium (1,000 mu g/kg f or infants and 1,800 mu g/kg for children) was injected either intramu scularly (in the deltoid muscle) or intravenously. Four venous plasma samples were obtained from each child 2-240 min after rocuronium admin istration. A mixed-effects population pharmacokinetic analysis was app lied to these values to determine bioavailability, absorption rate con stant, and time to peak Cp with intramuscular administration. Results: With intramuscular administration, rocuronium's bioavailability avera ged 82.6% and its absorption rate constant was 0.105 min(-1). Simulati on indicated that Cp peaked 13 min after rocuronium was given intramus cularly, and that 30 min after intramuscular administration, less than 4% of the administered dose remained to be absorbed from the intramus cular depot. Conclusions: After rocuronium is administered into the de ltoid muscle, plasma concentrations peak at 13 min, and approximately 80% of the administered drug is absorbed systemically.