title: Interstitial muscle concentrations of rocuronium under steady-state conditions in anaesthetized dogs: actual versus predicted values.
abstract: BACKGROUND
  The objective of this study was to compare rocuronium effect (C(e)) and peripheral (C(2)) compartment concentrations predicted by pharmacokinetic-pharmacodynamic (PK-PD) modelling with those measured in plasma (C(p)) and in the interstitial fluid of muscle tissue (C(ISF,u)) by microdialysis in anaesthetized dogs.
  
  
  METHODS
  After approval by the Animal Care Committee, eight adult male dogs with a body weight ranging from 7 to 18 kg were anaesthetized with pentobarbital. Each dog received a 2-min rocuronium infusion of 0.15 mg kg(-1) min(-1) followed by a 118-min infusion of 60 microg kg(-1) min(-1) via the right jugular vein. Arteriovenous gradient across the hindlimb was measured at 40, 60, 100 and 120 min. Three microdialysis samples were collected at 40-min intervals. Once the infusion stopped, arterial samples were collected every 2 min for the first 10 min and every 20 min for the next 120 min. Neuromuscular function was monitored using train-of-four stimulation until full recovery. Dogs were then killed and a biopsy of muscle tissue was performed (C(m)).
  
  
  RESULTS
  At steady state, the mean C(ISF,u) value was 1353 ng ml(-1). After correction for the unbound fraction in plasma, the mean C(e,corr) and C(2,corr) were 1681 and 1481 ng ml(-1), respectively. At the terminal sampling point, C(m) was 10-fold higher than C(p).
  
  
  CONCLUSIONS
  Unbound concentration of rocuronium measured in the muscle interstitial fluid under steady-state conditions confirms that parametric PK-PD modelling gives reliable estimates of effect site concentrations. Rocuronium accumulates in muscle tissue, probably by non-specific protein binding in the interstitial space.
authors.affiliation: Faculté de pharmacie, Université de Montréal, Montréal, Québec, Canada.
authors.forename: S
authors.initials: S
authors.lastname: Ezzine
authors.forename: F
authors.initials: F
authors.lastname: Varin
mesh_terms: D000732:Androstanols / Q000097:blood / Q000493:pharmacokinetics*; D000818:Animals; D004285:Dogs; D045604:Extracellular Fluid / Q000378:metabolism; D008297:Male; D017551:Microdialysis; D008954:Models, Biological; D018482:Muscle, Skeletal / Q000378:metabolism*; D009469:Neuromuscular Junction / Q000187:drug effects / Q000502:physiology; D003473:Neuromuscular Nondepolarizing Agents / Q000097:blood / Q000493:pharmacokinetics*; D000077123:Rocuronium
chemical_list: D000732:Androstanols; D003473:Neuromuscular Nondepolarizing Agents; D000077123:Rocuronium