Treating arrhythmias: an expert opinion

New oral anticoagulants: will they replace warfarin?

Vitamin K antagonists, such as warfarin, are considered to be the treatment of choice to prevent thromboembolic events, but problems, such as the need for frequent dose adjustment and monitoring of coagulation status, as well as multiple drug and food interactions, make their use difficult for both physician and patient. Two new anticoagulants are now being considered as possible replacements of vitamin K antagonists. Dabigatran, an oral direct thrombin inhibitor has already been approved in the USA for prevention of stroke in patients with atrial fibrillation. Rivaroxaban, a factor Xa inhibitor, and dabigatran are licensed in Europe and Canada for short-term thromboprophylaxis after elective hip or knee replacement surgery. The advantages of these drugs are that they are safe and effective, require no monitoring, have a direct mode of action against only one clotting factor (thrombin or factor Xa), have limited drug interactions, and have rapid peak blood levels. Based on the fact that dabigatran has already been approved for use in the USA, it would appear that it has an advantage over rivaroxaban in becoming the replacement drug for vitamin K antagonists.

Managing atrial fibrillation in the elderly: critical appraisal of dronedarone

Atrial fibrillation is the most commonly seen arrhythmia in the geriatric population and is associated with increased cardiovascular morbidity and mortality. Treatment of the elderly with atrial fibrillation remains challenging for physicians, because this unique subpopulation is characterized by multiple comorbidities requiring chronic use of numerous medications, which can potentially lead to severe drug interactions. Furthermore, age-related changes in the cardiovascular system as well as other physiological changes result in altered drug pharmacokinetics. Dronedarone is a new drug recently approved for the treatment of arrhythmias, such as atrial fibrillation and/or atrial flutter. Dronedarone is a benzofuran amiodarone analog which lacks the iodine moiety and contains a methane sulfonyl group that decreases its lipophilicity. These differences in chemical structure are responsible for making dronedarone less toxic than amiodarone which, in turn, results in fewer side effects. Adverse events for dronedarone include gastrointestinal side effects and rash. No dosage adjustments are required for patients with renal impairment. However, the use of dronedarone is contraindicated in the presence of severe hepatic dysfunction.

Mitochondrial oxidative stress and respiratory chain dysfunction account for liver toxicity during amiodarone but not dronedarone administration

The role played by oxidative stress in amiodarone-induced mitochondrial toxicity is debated. Dronedarone shows pharmacological properties similar to those of amiodarone but several differences in terms of toxicity. In this study, we analyzed the effects of the two drugs on liver mitochondrial function by administering an equivalent human dose to a rat model. Amiodarone increased mitochondrial H(2)O(2) synthesis, which in turn induced cardiolipin peroxidation. Moreover, amiodarone inhibited Complex I activity and uncoupled oxidative phosphorylation, leading to a reduction in the hepatic ATP content. We also observed a modification of membrane phospholipid composition after amiodarone administration. N-acetylcysteine completely prevented such effects. Although dronedarone shares with amiodarone the capacity to induce uncoupling of oxidative phosphorylation, it did not show any of the oxidative effects and did not impair mitochondrial bioenergetics. Our data provide important insights into the mechanism of mitochondrial toxicity induced by amiodarone. These results may greatly influence the clinical application and toxicity management of these two antiarrhythmic drugs.