Long-lasting Drug Interaction Between Warfarin and Amiodarone

Overview

Authors describe a case of drug interaction between amiodarone and warfarin in 66-year-old man with recurrentatrial fibrillation. In spite of a relatively low dose of warfarin, prothrombin time became extremely prolonged andbleeding manifestations occurred. Effects of the interaction persisted for a long time after the withdrawal of bothdrugs. Various approaches to oral anticoagulant reversal are discussed. Pharmacokinetics of both drugs is explained,as well as the mechanism of their interaction through cytochrome P450 inhibition in the liver. Authors emphasizethe great interindividual variability and long persistence of this interaction. It is necessary to consider carefully theindication of using these drugs together and when the use is inevitable, it is recommended to lower the warfarin doseto 50–70 % and to perform thorough and frequent INR monitoring.

Key words:
drug interaction, amiodaron, warfarin, cytochrome P450.