Single Copy Of Variant Cyp2a6 Alleles Does Not Confer Susceptibility To Liver Dysfunction In Patients Treated With Coumarin

Objective: Coumarin, used in the treatment of chronic venous diseases, is mainly metabolized to non-toxic 7-hydroxy-coumarin by CYP2A6. At least, 3 variant alleles, CYP2A6*2, CYP2A6*3 and CYP2A6*4A, have been shown to encode catalytically defective proteins. Sporadic elevation of liver enzymes has been reported on the chronic administration of coumarin. We sought to determine if susceptibility to coumarin-associated liver dysfunction is genetically determined by polymorphism in CYP2A6 and impairment of the 7-hydroxylation of coumarin. Additionally, we were interested in the effect of polymorphism on smoking because of the predominant role of CYP2A6 in the metabolism of nicotine. Methods: The investigation was performed prospectively within a randomized double-blind clinical trial of the coumarin-containing drug SB-LOT (90 mg coumarin + 540 mg troxerutin/d) vs. placebo in 231 German patients with chronic venous insufficiency. Monitoring of the hepatic status involved regular measurements of liver function during the 16-week treatment. Geno-typing of CYP2A6 was carried out by means of PCR and confirmed by DNA sequencing analysis. Results: The allelic frequencies of the variant CYP2A6*2 and CYP2A6*3 alleles were 0.023 and 0.014, respectively. There was no significant difference in the incidence of liver dysfunction between heterozygotes with CYP2A6*2, CYP2A6*3 and wild-type homozygotes. CYP2A6 polymorphism had no significant effect on smoking behavior. Conclusion: No evidence was obtained that the studied polymorphism in CYP2A6 is a determinant of the coumarin-associated liver dysfunction.