title: Meta-analysis of the influence of MDR1 C3435T polymorphism on digoxin pharmacokinetics and MDR1 gene expression.
abstract: OBJECTIVE
  Studies revealing conflicting results of the functional significance of MDR1 exon 26 C3435T SNP on the disposition of digoxin in different ethnic groups led us to perform a meta-analysis on published data investigating the influence of C3435T SNP on the pharmacokinetics of digoxin and the expression of MDR1.
  
  
  METHODS
  Meta-analysis was performed on data from published studies investigating the influence of MDR1 C3435T SNP on digoxin pharmacokinetics, as well as MDR1 expression in Caucasian and Japanese populations. The following outcomes were included: exposures to digoxin measured by area under the concentration-time curve and maximum concentration, the mean intestinal MDR1 mRNA expression and P-gp expression in the absence of digoxin administration.
  
  
  RESULTS
  The overall results of the meta-analysis in Caucasian and Japanese subjects suggested no major influence of the C3435T SNP on exposure levels of digoxin as determined by AUC(0-4 h) or AUC(0-24 h) although C(max) values for digoxin were lower in wild-type (CC) subjects compared with subjects harbouring TT genotypes. Subgroup analysis by ethnic populations showed the oral availability of digoxin to be lower in wild-type Caucasian populations compared with wild-type Japanese subjects. No causal relationships were detected between the C3435T SNP and MDR1 mRNA or protein expression.
  
  
  CONCLUSIONS
  Our meta-analysis of available studies indicates that the synonymous MDR1 C3435T SNP does not affect the pharmacokinetics of digoxin and the expression of MDR1 mRNA. Future studies should focus on the impact of MDR1 haplotypes on the pharmacokinetics of MDR1 substrates rather than the C3435T SNP alone.
authors.affiliation: Laboratory of Clinical Pharmacology, Division of Clinical Trials and Epidemiological Sciences, National Cancer Centre, Singapore. ctebal@nccs.com.sg
authors.forename: Balram
authors.initials: B
authors.lastname: Chowbay
authors.forename: Huihua
authors.initials: H
authors.lastname: Li
authors.forename: Machin
authors.initials: M
authors.lastname: David
authors.forename: Yin Bun
authors.initials: YB
authors.lastname: Cheung
authors.forename: Edmund J D
authors.initials: EJ
authors.lastname: Lee
mesh_terms: D000284:Administration, Oral; D019540:Area Under Curve; D004077:Digoxin / Q000008:administration & dosage / Q000493:pharmacokinetics*; D004791:Enzyme Inhibitors / Q000493:pharmacokinetics*; D005786:Gene Expression Regulation / Q000235:genetics; D019450:Genes, MDR / Q000235:genetics*; D005838:Genotype; D006801:Humans; D007564:Japan / Q000208:ethnology; D020641:Polymorphism, Single Nucleotide / Q000235:genetics*; D012333:RNA, Messenger / Q000032:analysis; D044465:White People / Q000208:ethnology
chemical_list: D004791:Enzyme Inhibitors; D012333:RNA, Messenger; D004077:Digoxin