Interactions between warfarin-sodium(warfarin) and Amiodarone (amiodarone)
amiodarone and warfarin (Major Drug-Drug)
MONITOR CLOSELY: Amiodarone may increase the pharmacologic effects of warfarin by inhibiting CYP450 2C9 hepatic metabolism of S-warfarin. Similar effects may also occur with other oral anticoagulants, resulting in significant hypoprothrombinemia and bleeding. When amiodarone is added to an anticoagulant regimen, increased anticoagulant effects may become apparent within one to several weeks and may persist for months after the amiodarone is discontinued. The effects of this interaction are highly variable - while some patients are asymptomatic, serious and life-threatening bleeding complications have been reported in others. Patients who are poor CYP450 2C9 metabolizers may have a higher risk of bleeding and a faster onset of the interaction.
MANAGEMENT: An empiric 30% to 50% reduction in anticoagulant dosage has been recommended, in addition to frequent monitoring of the patient and the prothrombin time or International Normalized Ratio (INR). Patients should be advised to notify their physician promptly if they experience any signs of excessive anticoagulation such as unusual or prolonged bleeding, bruising, vomiting, change in stool or urine color, headache, dizziness, or weakness.
