A 74-year-old woman is admitted to the hospital for an episode of paroxysmal atrial fibrillation that caused palpitations and dizziness. She is started on metoprolol and amiodarone. Her past medical history is also significant for recurrent deep venous thrombosis 6 months ago. The patient has been on chronic anticoagulation therapy with a stable dose of warfarin since then. Her primary care physician checks her International Normalized Ratio every month; it is 2.6 at the time of admission. Echocardiogram shows left atrial enlargement and left ventricular ejection fraction of 45%. She feels well the following day and is ready for discharge. Which of the following is the best management for this patient's anticoagulation?

Question

A 74-year-old woman is admitted to the hospital for an episode of paroxysmal atrial fibrillation that caused palpitations and dizziness.  She is started on metoprolol and amiodarone.  Her past medical history is also significant for recurrent deep venous thrombosis 6 months ago.  The patient has been on chronic anticoagulation therapy with a stable dose of warfarin since then.  Her primary care physician checks her International Normalized Ratio every month; it is 2.6 at the time of admission.  Echocardiogram shows left atrial enlargement and left ventricular ejection fraction of 45%.  She feels well the following day and is ready for discharge.  Which of the following is the best management for this patient's anticoagulation?

Quizplus · Accepted Answer

Explanation: 11ec2b69_be03_c0e4_8f63_7149fd26ca61_MD0005_00 Warfarin interacts with several prescription and over-the-counter medications, leading to over/under-anticoagulation and increased bleeding risk (with or without a change in the prothrombin time). Therefore, new medications should always be added cautiously in patients on chronic anticoagulation with warfarin. Amiodarone slows warfarin metabolism (and increases serum concentration) in the liver by inhibiting the cytochrome enzyme system and can lead to over-anticoagulation in patients maintained on a stable dose of warfarin. Although large-scale clinical studies for dosing of warfarin along with amiodarone are lacking, it is recommended that the warfarin dose be reduced by 25%-50% to compensate for the increase in serum concentration of warfarin after initiating amiodarone therapy. The prothrombin time/International Normalized Ratio (INR) should be followed closely for the next several weeks until a new stable dosing regimen for warfarin has been established. (Choice A) Maintaining the current dose of warfarin and rechecking the INR in 2 weeks will lead to over-anticoagulation with a potential risk of bleeding complications. (Choices C and D) Increased warfarin dose should be considered if the patient is started on new medications that can decrease warfarin effect by enhanced metabolism and/or a decrease in the serum concentration of warfarin (eg, rifampin, phenobarbital, oral contraceptives). (Choice E) Completely stopping warfarin while starting amiodarone is not recommended, as this can lead to under-anticoagulation for several days with an increased risk of systemic thromboembolism. Educational objective: It is recommended that the warfarin dose be reduced by 25%-50% to compensate for the increase in serum concentration of warfarin after initiating amiodarone therapy. References: Clinical observations with the amiodarone/warfarin interaction: dosing relationships with long-term therapy. (http://www.ncbi.nlm.nih.gov/pubmed/11796427)

A 74-Year-Old Woman Is Admitted to the Hospital for an Episode