AMIODARONE POTENTIATES WARFARIN ANTICOAGULATION

First report of an interaction. confirmed by re-challenge After a cerebrovascular accident caused by an embolus, a 57-year~ld woman was treated with warfarin J-Sms / day. As an fCC showed episodes of supraventricular tachycardia. sinus bradycardia and atrial fibrillation, she had a permanent pacemaker inserted, and then was given amiodarone 200mg tid. The British corrected ratio of prothrombin times (BCR) increased from 1.5 to 5 within 5 days, and GI bleeding occurred, necessitating phytomenadione(vitamin K I). One month later, aner another cerebrovascular accident, warfarin was restarted. Aner 3 days, amiodarone was also given. W ithin 4 days, the 8eR rose from 2.5 to 4.5. To confirm an amiodarone-warfarin interaction. rabbits stabilised on O.4mg of warfarin had a S-rold increase in BCRs within 2 days of starting amiodarone 35mg/day . • Amiodarone is highly ( )o 90%) protein bound in the blood. A possible explanation of the interaction is therefore that it displaces warfarin from protein-binding sites,' Rces, A: ec aI .' British Medical Journal 282, 17S6 00 May 19111)J

6 , INPHARMA 6Juo 1981 0156-2703/ 81 / 0606-0006 $00.50/0 t:l ADIS Press