Background Amiodarone and dronedarone decrease the risk of recurrences in patients with paroxysmal or persistent atrial fibrillation or atrial flutter. Both drugs are P-glycoprotein inhibitors and they are substrate/inhibitor of CYP3A4.

Purpose To assess the safety profile of amiodarone and dronedarone in patients treated with oral vitamin K antagonists.

Materials and methods Prospective study in a hospital for 12 months. Data collected: demographics and INR levels. Patients included: age >18 treated with acenocoumarol who were started on dronedarone or amiodarone. In patients with AF an INR of 2.0–3.0 was considered as therapeutic. We included patients who had an INR stable for at least 3 months prior to starting treatment with either drug. We monitored the INR for a month after initiation of antiarrhythmic treatment. We considered the effect of other factors in altering the INR. Safety profile of the drugs: class A-mild (INR: 3–4), class B-moderate (INR: 4–5), class C-severe (INR: >5). We considered an INR <3 a lack of interaction.

Results Patients included: 30. Patients treated with amiodarone: 18, 61.1% (11/18) females, mean age (years): 72 (range: 59–89). Patients treated with dronedarone: 12, 33.3% (4/12) females, mean age (years): 69 (range: 37–80). Patients treated with amiodarone, class A: 5 (27.8%), class B: 6 (33.3%), class C: 7 (38.9%). Patients treated with dronedarone, class A: 8 (66.7%), class B: 3 (25%), class C: 0, absence of interaction: 1 (8.3%). INR remained stable for at least 3 months in all cases after an alteration of INR had been detected and the pattern of acenocoumarol had been changed. No effects were observed due to other drugs, food or lifestyle changes in these patients. INR was altered only with the use of dronedarone or amiodarone.

Conclusions Dronedarone had a better safety profile than amiodarone in elderly patients treated with acenocoumarol. However, further studies should provide a greater degree of evidence in this regard and clarify the mechanisms of action involved in this interaction.

No conflict of interest.