The potentiation of acenocoumarol anticoagulant effect by amiodarone

Out of 690 patients (337 males and 353 females) on long-term acenocoumarol therapy, 80 (35 males and 45 females) were taking amiodarone. Forty patients had started amiodarone treatment while being treated with acenocoumarol. Of these, nine patients had begun amiodarone treatment while taking acenocoumarol. The relation between the daily dose of acenocoumarol and the prothrombin ratio (AC dose/PR ratio) has been considered a useful indicator to study the interaction between amiodarone and acenocoumarol. Differences of acenocoumarol daily dose between takers and non-takers of amiodarone were statistically significant (t = 5.35; P less than 0.001) for the whole population, for all the age groups, and also among males (t = 2.43; P less than 0.01) as well as among females (t = 5.38; P less than 0.001). Out of 40 patients chronically treated with acenocoumarol in whom amiodarone was instituted, 32 showed a decrease of the AC dose/PR ratio, while in eight patients no change was recorded (paired t-test, t = 5.82; P less than 0.001). In 15 patients who were being concomitantly treated with acenocoumarol and amiodarone, amiodarone was discontinued. An increase of the AC dose/PR ratio was recorded (paired t-test, t = 4.01; P less than 0.001). Nine patients had started treatment with amiodarone while receiving acenocoumarol and a decrease of the AC dose/PR ratio was documented; amiodarone was discontinued some months later, and an increase of the AC dose/PR ratio was seen.