Q: 64 year old male is admitted to ICU with atrial fibrillation and rapid ventricular rate (A.fib-RVR). Patient is chronically on warfarin at home for previous episodes of Deep Vein Thrombosis (DVTs) and pulmonary embolisms (PEs). Cardiology service decides to initiate Amiodarone bolus followed by drip. As interaction between amiodarone and warfarin is well known, how much should be the dose of warfarin cut done?
A) Completely stop
B) cut by 50%
C) cut by 25%
D) No adjustment needed
E) Tell cardiology they are wrong to start Amiodarone!
As Amiodarone may potentiates the effect of warfarin, it's dose should be cut back by about 25 percent. This inference is obtained from the cohort of 754 patients of a Swedish registry, who were on chronic warfarin treatment and in whom amiodarone was started. Though, close monitoring of INR is advised. Another caution is to closely monitor the thyroid function. Amiodarone is prone to cause thyrotoxicosis which may potentiates the effect of warfarin.
E is not a good practice!
1. Holm J, Lindh JD, Andersson ML, Mannheimer B. The effect of amiodarone on warfarin anticoagulation: a register-based nationwide cohort study involving the Swedish population. J Thromb Haemost 2017; 15:446.
2. Kurnik D, Loebstein R, Farfel Z, et al. Complex drug-drug-disease interactions between amiodarone, warfarin, and the thyroid gland. Medicine (Baltimore) 2004; 83:107.