Potential interaction between acenocoumarol and diclofenac, naproxen and ibuprofen and role of CYP2C9 genotype.

NSAIDs are reported to increase the risk of bleeding in coumarin users. The mechanism underlying this risk is inhibition of platelet aggregation, however a pharmacokinetic mechanism resulting in an increased International Normalised Ratio (INR) was proposed in some case reports in warfarin treated patients. In this retrospective cohort study the influence of diclofenac, naproxen and ibuprofen on the INR of outpatients stabilised on acenocoumarol therapy was investigated.