title: Population analysis of the non linear red blood cell partitioning and the concentration-effect relationship of draflazine following various infusion rates.
abstract: OBJECTIVE
  To investigate the impact of the specific red blood cell binding on the pharmacokinetics and pharmacodynamics of the nucleoside transport inhibitor draflazine after i.v. administration at various infusion rates. It was also aimed to relate the red blood cell (RBC) occupancy of draflazine to the ex vivo measured adenosine breakdown inhibition (ABI).
  
  
  METHODS
  Draflazine was administered to healthy volunteers as a 15-min i.v. infusion of 0.25, 0.5, 1, 1.5 and 2.5 mg immediately followed by an infusion of the same dose over 1 h. Plasma and whole blood concentrations were measured up to 120 h post dose, and were related to the ex vivo measured ABI, serving as a pharmacodynamic endpoint. The capacity-limited specific binding of draflazine to the nucleoside transporter located on the erythrocytes was evaluated by a population approach.
  
  
  RESULTS
  The estimate of the population parameter typical value (%CV) of the binding constant Kd and the maximal specific binding capacity (Bmax) was 0.385 (3.5) ng ml-1 plasma and 158 (2.1) ng ml-1 RBC, respectively. The non-specific binding was low. The specific binding to the erythrocytes was a source of non-linearity in the pharmacokinetics of draflazine. The total plasma clearance of draflazine slightly decreased with increasing doses, whereas the total clearance in whole blood increased with increasing doses. The sigmoidal Emax equation was used to relate the plasma and whole blood concentration of draflazine to the ex vivo determined ABI. In plasma, typical values (%CV) of Emax, IC50 and Hill factor were 81.4 (1.9)%, 3.76 (9.3) ng ml-1 and 1.06 (3.4), respectively. The relationship in whole blood was much steeper with population parameter typical values (%CV) of Emax, IC50 and Hill factor of 88.2 (2.0)%, 65.7 (2.8) ng ml-1 and 4.47 (5.5), respectively. The RBC occupancy of draflazine did not coincide with the ex vivo measured ABI. The observed relationship between RBC occupancy and ABI was not directly proportional but similar for all studied infusion schemes.
  
  
  CONCLUSIONS
  The findings of this study show that the occupancy of the nucleoside transporter by draflazine should be at least 90% in order to inhibit substantially adenosine breakdown in vivo. On the basis of these findings it is suggested that a 15 min infusion of 1 mg draflazine followed by an infusion of 1 mg h-1 could be appropriate in patients undergoing a coronary artery bypass grafting.
authors.affiliation: Janssen Research Foundation, Beerse, Belgium.
authors.forename: E
authors.initials: E
authors.lastname: Snoeck
authors.forename: V
authors.initials: V
authors.lastname: Piotrovskij
authors.forename: P
authors.initials: P
authors.lastname: Jacqmin
authors.forename: A
authors.initials: A
authors.lastname: Van Peer
authors.forename: M
authors.initials: M
authors.lastname: Danhof
authors.forename: K
authors.initials: K
authors.lastname: Ver Donck
authors.forename: R
authors.initials: R
authors.lastname: Woestenborghs
authors.forename: H
authors.initials: H
authors.lastname: Van Belle
authors.forename: L
authors.initials: L
authors.lastname: Van Bortel
authors.forename: R
authors.initials: R
authors.lastname: Van Gool
authors.forename: A G
authors.initials: AG
authors.lastname: Dupont
authors.forename: J
authors.initials: J
authors.lastname: Heykants
mesh_terms: D000241:Adenosine / Q000097:blood; D000328:Adult; D019540:Area Under Curve; D001667:Binding, Competitive; D015331:Cohort Studies; D004305:Dose-Response Relationship, Drug; D004311:Double-Blind Method; D004906:Erythrocyte Count / Q000187:drug effects; D004912:Erythrocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D006207:Half-Life; D006801:Humans; D007275:Injections, Intravenous; D008297:Male; D008875:Middle Aged; D010879:Piperazines / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics* / Q000494:pharmacology; D010975:Platelet Aggregation Inhibitors / Q000097:blood / Q000493:pharmacokinetics* / Q000494:pharmacology; D012044:Regression Analysis; D012984:Software; D044465:White People
chemical_list: D010879:Piperazines; D010975:Platelet Aggregation Inhibitors; C072040:draflazine; D000241:Adenosine