title: Bioavailability of intramuscular rocuronium in infants and children.
abstract: BACKGROUND
  Intramuscular rocuronium, in doses of 1,000 microg/kg in infants and 1,800 microg/kg in children, produces complete twitch depression in 5-6 min. To determine the rate and extent of absorption of rocuronium after intramuscular administration, blood was sampled at various intervals after rocuronium administration by both intramuscular and intravenous routes to determine plasma concentrations (Cp) of rocuronium.
  
  
  METHODS
  Twenty-nine pediatric patients ages 3 months to 5 yr were anesthetized with N2O and halothane. The trachea was intubated, ventilation was controlled, and adductor pollicis twitch tension was measured. When anesthetic conditions were stable, rocuronium (1,000 microg/kg for infants and 1,800 microg/kg for children) was injected either intramuscularly (in the deltoid muscle) or intravenously. Four venous plasma samples were obtained from each child 2-240 min after rocuronium administration. A mixed-effects population pharmacokinetic analysis was applied to these values to determine bioavailability, absorption rate constant, and time to peak Cp with intramuscular administration.
  
  
  RESULTS
  With intramuscular administration, rocuronium's bioavailability averaged 82.6% and its absorption rate constant was 0.105 min(-1). Simulation indicated that Cp peaked 13 min after rocuronium was given intramuscularly, and that 30 min after intramuscular administration, less than 4% of the administered dose remained to be absorbed from the intramuscular depot.
  
  
  CONCLUSIONS
  After rocuronium is administered into the deltoid muscle, plasma concentrations peak at 13 min, and approximately 80% of the administered drug is absorbed systemically.
authors.affiliation: Department of Anesthesia, University of California, San Francisco 94143-0648, USA.
authors.forename: L M
authors.initials: LM
authors.lastname: Reynolds
authors.forename: M
authors.initials: M
authors.lastname: Lau
authors.forename: R
authors.initials: R
authors.lastname: Brown
authors.forename: A
authors.initials: A
authors.lastname: Luks
authors.forename: M
authors.initials: M
authors.lastname: Sharma
authors.forename: D M
authors.initials: DM
authors.lastname: Fisher
mesh_terms: D000732:Androstanols / Q000008:administration & dosage / Q000009:adverse effects / Q000493:pharmacokinetics*; D001682:Biological Availability; D002675:Child, Preschool; D006801:Humans; D007223:Infant; D007273:Injections, Intramuscular; D008657:Metabolic Clearance Rate; D003473:Neuromuscular Nondepolarizing Agents / Q000493:pharmacokinetics*; D000077123:Rocuronium
chemical_list: D000732:Androstanols; D003473:Neuromuscular Nondepolarizing Agents; D000077123:Rocuronium