title: Tacrolimus pharmacogenetics: polymorphisms associated with expression of cytochrome p4503A5 and P-glycoprotein correlate with dose requirement.
abstract: BACKGROUND
  There is marked heterogeneity in blood concentrations of tacrolimus following standard body-weight-based dosing. This is most apparent in black patients, who have a higher dose requirement when compared with other ethnic groups. Differences in intestinal P-glycoprotein and hepatic and intestinal cytochrome P4503A activity have been postulated as contributing to this problem.
  
  
  METHODS
  The dose-normalized blood concentrations of tacrolimus at 3 months after renal transplantation were related to CYP3AP1 and multiple drug resistance (MDR)-1 genotypes determined by polymerase chain reaction followed by restriction fragment length polymorphism analysis.
  
  
  RESULTS
  We found that a single nucleotide polymorphism in the CYP3AP1 pseudogene (A/G(44)) that previously has been noted to be more common in African Americans and strongly associated with hepatic CYP3A5 activity correlated well with the tacrolimus dose requirement. A weaker association was found for a polymorphism in the MDR-1 gene, which influences intestinal P-glycoprotein expression.
  
  
  CONCLUSIONS
  The CYP3AP1 genotype is a major factor in determining the dose requirement for tacrolimus, and genotyping may be of value in planning patient-specific drug dosing.
authors.affiliation: Division of Renal Medicine St. George's Hospital Medical School, London, United Kingdom. imacphee@sghms.ac.uk
authors.forename: Iain A M
authors.initials: IA
authors.lastname: Macphee
authors.forename: Salim
authors.initials: S
authors.lastname: Fredericks
authors.forename: Tracy
authors.initials: T
authors.lastname: Tai
authors.forename: Petros
authors.initials: P
authors.lastname: Syrris
authors.forename: Nicholas D
authors.initials: ND
authors.lastname: Carter
authors.forename: Atholl
authors.initials: A
authors.lastname: Johnston
authors.forename: Lawrence
authors.initials: L
authors.lastname: Goldberg
authors.forename: David W
authors.initials: DW
authors.lastname: Holt
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism*; D000293:Adolescent; D000328:Adult; D000368:Aged; D044466:Asian People / Q000235:genetics; D044383:Black People / Q000235:genetics; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D005260:Female; D019450:Genes, MDR / Q000502:physiology; D005838:Genotype; D006801:Humans; D008297:Male; D008875:Middle Aged; D010597:Pharmacogenetics; D020641:Polymorphism, Single Nucleotide / Q000502:physiology*; D011544:Pseudogenes / Q000235:genetics; D016559:Tacrolimus / Q000008:administration & dosage* / Q000627:therapeutic use; D044465:White People / Q000235:genetics; D001741:Black or African American
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D003577:Cytochrome P-450 Enzyme System; C104464:CYP3A protein, human; C510164:CYP3A5 protein, human; D051544:Cytochrome P-450 CYP3A; D016559:Tacrolimus