title: Effect of CYP2D6 polymorphism on pharmacokinetics of a novel ACAT inhibitor, pactimibe and its unique metabolite, R-125528.
abstract: OBJECTIVE
  Pactimibe is a novel ACAT inhibitor. The pharmacokinetics of pactimibe and its pharmacologically inactive plasma metabolite, R-125528, of which the main clearance pathway is CYP2D6, was affected by coadministration of quinidine. The aim of this study was to investigate the influence of CYP2D6 polymorphism on pharmacokinetics of pactimibe and R-125528. In addition, exposure was examined after multiple doses of pactimibe sulfate in CYP2D6 poor metabolizer (PMs).
  
  
  METHODS
  24 healthy male Caucasian volunteers, genotyped as extensive, intermediate, and poor metabolizers, were received single dose of 25 mg pactimibe. In a multiple-dose study, six CYP2D6 PMs received 100 mg pactimibe for 21 days and exposure of pactimibe and R-125528 was examined.
  
  
  RESULTS
  In contrast to the mild 1.7-fold increase in AUC0-inf of pactimibe, a marked 3.1-fold increase in AUC0-tz of R-125528 was observed in CYP2D6 PMs. After multiple doses of 100 mg pactimibe to CYP2D6 PMs, the accumulation ratio of R-125528 reached 8.8-fold, however, the exposure of R-125528 in CYP2D6 PMs was covered by the exposure in additional metabolite safety testing.
  
  
  CONCLUSIONS
  Although CYP2D6 polymorphism greatly affected the pharmacokinetics of R-125528 rather than pactimibe, the exposure in CYP2D6 PMs after a multiple dose of 100 mg pactimibe sulfate was covered by additional non-clinical metabolite safety testing. The finding is clinically informative with respect to the safety testing of drug metabolite present at disproportionately high levels in a special population with specific genetic back ground.
authors.affiliation: Drug Metabolism & Pharmacokinetics Research Laboratories, Daiichi Sankyo Co., Ltd., Tokyo, Japan. kotsuma.masakatsu.gu@daiichisankyo.co.jp
authors.forename: M
authors.initials: M
authors.lastname: Kotsuma
authors.forename: T
authors.initials: T
authors.lastname: Tokui
authors.forename: S
authors.initials: S
authors.lastname: Freudenthaler
authors.forename: K
authors.initials: K
authors.lastname: Nishimura
mesh_terms: D000293:Adolescent; D000328:Adult; D000473:Alkanes / Q000097:blood / Q000493:pharmacokinetics*; D019540:Area Under Curve; D019389:Cytochrome P-450 CYP2D6 / Q000235:genetics* / Q000378:metabolism / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D005838:Genotype; D006207:Half-Life; D006801:Humans; D007210:Indoleacetic Acids / Q000378:metabolism / Q000493:pharmacokinetics* / Q000494:pharmacology; D007211:Indoles / Q000097:blood / Q000493:pharmacokinetics*; D016014:Linear Models; D008297:Male; D011110:Polymorphism, Genetic; D002785:Sterol O-Acyltransferase / Q000037:antagonists & inhibitors; D055815:Young Adult
chemical_list: D000473:Alkanes; D007210:Indoleacetic Acids; D007211:Indoles; C531582:R-125528; C509302:pactimibe; D019389:Cytochrome P-450 CYP2D6; D002785:Sterol O-Acyltransferase