title: Explaining variability in ciclosporin exposure in adult kidney transplant recipients.
abstract: OBJECTIVE
  Optimal ciclosporin A (CsA) exposure in kidney transplant recipients is difficult to attain because of variability in CsA pharmacokinetics. A better understanding of the variability in CsA exposure could be a good means of individualizing therapy. Specifically, genetic variability in genes involved in CsA metabolism could explain exposure differences. Therefore, this study is aimed at identifying a relationship between genetic polymorphisms and the variability in CsA exposure, while accounting for non-genetic sources of variability.
  
  
  METHODS
  De novo kidney transplant patients (n = 33) were treated with CsA for 1 year and extensive blood sampling was performed on multiple occasions throughout the year. The effects of the non-genetic covariates hematocrit, serum albumin concentration, cholesterol, demographics (i.e., body weight), CsA dose interval, prednisolone dose and genetic polymorphisms in genes encoding ABCB1, CYP3A4, CYP3A5, and PXR on CsA pharmacokinetics were studied using non-linear mixed effect modeling.
  
  
  RESULTS
  The pharmacokinetics of CsA were described by a two-compartment disposition model with delayed absorption. Body weight was identified as the most important covariate and explained 35% of the random inter-individual variability in CsA clearance. Moreover, concurrent prednisolone use at a dosage of 20 mg/day or higher was associated with a 22% higher clearance of CsA, hence lower CsA exposure. In contrast, no considerable genotype effects (i.e., greater than 30-50%) on CsA clearance were found for the selected genes.
  
  
  CONCLUSIONS
  It appears that the selected genetic markers explain variability in CsA exposure insufficiently to be of clinical relevance. Therefore, therapeutic drug monitoring is still required to optimize CsA exposure after administration of individualized doses based on body weight and, as this study suggests, co-administration of prednisolone.
authors.affiliation: Department of Clinical Pharmacy and Toxicology, Leiden University Medical Center, Albinusdreef 2, 2333 ZA, Leiden, The Netherlands. r.r.press@lumc.nl
authors.forename: Rogier R
authors.initials: RR
authors.lastname: Press
authors.forename: Bart A
authors.initials: BA
authors.lastname: Ploeger
authors.forename: Jan
authors.initials: J
authors.lastname: den Hartigh
authors.forename: T
authors.initials: T
authors.lastname: van der Straaten
authors.forename: Hans
authors.initials: H
authors.lastname: van Pelt
authors.forename: Meindert
authors.initials: M
authors.lastname: Danhof
authors.forename: Hans
authors.initials: H
authors.lastname: de Fijter
authors.forename: Henk-Jan
authors.initials: HJ
authors.lastname: Guchelaar
mesh_terms: D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics; D000328:Adult; D000368:Aged; D001835:Body Weight; D016572:Cyclosporine / Q000008:administration & dosage* / Q000097:blood / Q000493:pharmacokinetics*; D051544:Cytochrome P-450 CYP3A / Q000235:genetics; D004334:Drug Administration Schedule; D005260:Female; D016231:Fluorescence Polarization Immunoassay; D005838:Genotype; D006801:Humans; D007166:Immunosuppressive Agents / Q000008:administration & dosage* / Q000097:blood / Q000493:pharmacokinetics*; D016030:Kidney Transplantation / Q000276:immunology; D008297:Male; D008875:Middle Aged; D011110:Polymorphism, Genetic; D011239:Prednisolone / Q000008:administration & dosage / Q000493:pharmacokinetics; D000077297:Pregnane X Receptor; D011987:Receptors, Steroid / Q000235:genetics; D016019:Survival Analysis
chemical_list: C513055:ABCB1 protein, human; D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D007166:Immunosuppressive Agents; D000077297:Pregnane X Receptor; D011987:Receptors, Steroid; D016572:Cyclosporine; D011239:Prednisolone; C510164:CYP3A5 protein, human; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human