title: Pharmacokinetic-pharmacodynamic relationships of imatinib and its main metabolite in patients with advanced gastrointestinal stromal tumors.
abstract: OBJECTIVE
  This study explored factors affecting the pharmacokinetic variability of imatinib and CGP 74588, and the pharmacokinetic-pharmacodynamic correlations in patients with advanced gastrointestinal stromal tumors.
  
  
  METHODS
  Thirty-five patients with advanced gastrointestinal stromal tumors received 400 mg of imatinib daily. Six blood samples were drawn: before intake, during 1- to 3- and 6- to 9-hour intervals after intake on day 1, and before intake on days 2, 30, and 60. Plasma imatinib and CGP 74588 concentrations were quantified by reverse-phase high-performance liquid chromatography coupled with tandem mass spectrometry, and analyzed by the population pharmacokinetic method (NONMEM program). The influence of 17 covariates on imatinib clearance (CL) and CGP 74588 clearance (CLM/fm) was studied. These covariates included clinical and biological variables and occasion (OCC = 0 for pharmacokinetic data corresponding to the first administration, or OCC = 1 for the day 30 or 60 administrations).
  
  
  RESULTS
  The best regression formulas were: CL (L/h) = 7.97 (AAG/1.15)(-0.52), and CLM/fm (L/h) = 58.6 (AAG/1.15)(-0.60) x 0.55(OCC), with the plasma alpha1-acid glycoprotein (AAG) levels indicating that both clearance values decreased at a higher AAG level. A significant time-dependent decrease in CLM/fm was evidenced with a mean (+SD) CGP 74588/imatinib area under the curve (AUC) ratio of 0.25 (+/-0.07) at steady state, compared with 0.14 (+/-0.03) on day 1. Hematologic toxicity was correlated with pharmacokinetic variables: the correlation observed with the estimated unbound imatinib AUC at steady-state (r = 0.56, P < 0.001) was larger than that of the total imatinib AUC (r = 0.32, NS).
  
  
  CONCLUSIONS
  The plasma AAG levels influenced imatinib pharmacokinetics. A protein-binding phenomenon needs to be considered when exploring the correlations between pharmacokinetics and pharmacodynamics.
authors.affiliation: Hospital Henri-Mondor, Créteil, France, EA3035, Institut Claudius-Regaud, Toulouse, France.
authors.forename: Catherine
authors.initials: C
authors.lastname: Delbaldo
authors.forename: Etienne
authors.initials: E
authors.lastname: Chatelut
authors.forename: Micheline
authors.initials: M
authors.lastname: Ré
authors.forename: Alain
authors.initials: A
authors.lastname: Deroussent
authors.forename: Sophie
authors.initials: S
authors.lastname: Séronie-Vivien
authors.forename: Aurore
authors.initials: A
authors.lastname: Jambu
authors.forename: Patrice
authors.initials: P
authors.lastname: Berthaud
authors.forename: Axel
authors.initials: A
authors.lastname: Le Cesne
authors.forename: Jean-Yves
authors.initials: JY
authors.lastname: Blay
authors.forename: Gilles
authors.initials: G
authors.lastname: Vassal
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000970:Antineoplastic Agents / Q000097:blood / Q000493:pharmacokinetics* / Q000627:therapeutic use* / Q000633:toxicity; D001549:Benzamides; D005260:Female; D046152:Gastrointestinal Stromal Tumors / Q000188:drug therapy* / Q000473:pathology; D006801:Humans; D000068877:Imatinib Mesylate; D008297:Male; D008657:Metabolic Clearance Rate; D008875:Middle Aged; D018579:Patient Selection; D010879:Piperazines / Q000097:blood / Q000493:pharmacokinetics* / Q000627:therapeutic use* / Q000633:toxicity; D011743:Pyrimidines / Q000097:blood / Q000493:pharmacokinetics* / Q000627:therapeutic use* / Q000633:toxicity; D015203:Reproducibility of Results
chemical_list: D000970:Antineoplastic Agents; D001549:Benzamides; D010879:Piperazines; D011743:Pyrimidines; D000068877:Imatinib Mesylate