Dronedarone for maintenance of sinus rhythm in atrial fibrillation or flutter

Benzofuran derivatives and the thyroid

Amiodarone and dronedarone are two clinically important benzofuran derivatives. Amiodarone has been used widely for treating resistant tachyarrhythmias in the past three decades. However amiodarone and its main metabolically active metabolite desethylamiodarone can adversely affect many organs, including the thyroid gland. Amiodarone-induced thyroid disorders are common and often present as a management challenge for endocrinologists. The pathogenesis of amiodarone-induced thyroid dysfunction is complex but the inherent effects of the drug itself as well as its high iodine content appear to play a central role. The non-iodinated dronedarone also exhibits anti-arrhythmic properties but appears to be less toxic to the thyroid. This review describes the biochemistry of benzofuran derivatives, including their pharmacology and the physiology necessary for understanding the cellular mechanisms involved in their actions. The known effects of these compounds on thyroid action are described. Recommendations for management of amiodarone-induced hypothyroidism and thyrotoxicosis are suggested. Dronedarone appears to be an alternative but less-effective anti-arrhythmic agent and it does not have adverse effects on thyroid function. It may have a future role as an alternative agent in patients being considered for amiodarone therapy especially those at high risk of developing thyroid dysfunction but not in severe heart failure.

The role of thyroid hormone nuclear receptors in the heart: evidence from pharmacological approaches

This review evaluates the hypothesis that the cardiac effects of amiodarone can be explained—at least partly—by the induction of a local ‘hypothyroid-like condition’ in the heart. Evidence supporting the hypothesis comprises the observation that amiodarone exerts an inhibitory effect on the binding of T3 to thyroid hormone receptors (TR) alpha-1 and beta-1 in vitro, and on the expression of particular T3-dependent genes in vivo. In the heart, amiodarone decreases heart rate and alpha myosin heavy chain expression (mediated via TR alpha-1), and increases sarcoplasmic reticulum calcium-activated ATPase and beta myosin heavy chain expression (mediated via TR beta-1). Recent data show a significant similarity in expression profiles of 8,435 genes in the heart of hypothyroid and amiodarone-treated animals, although similarities do not always exist in transcripts of ion channel genes. Induction of a hypothyroid cardiac phenotype by amiodarone may be advantageous by decreasing energy demands and increasing energy availability.

New horizons in antiarrhythmic therapy: will novel agents overcome current deficits?

Pharmacologic antiarrhythmic therapy is the most commonly used treatment in most patients with atrial fibrillation (AF), but currently available agents are limited by risks that may offset the benefits of sinus rhythm. The development of antiarrhythmic agents with the potential for fewer adverse ventricular effects and less extracardiac toxicity is a primary aim of current investigations. At present, pharmacologic research is actively focused on developing antiarrhythmic agents with multiple or novel ion channel effects. There are 4 agents that act by simultaneously blocking multiple ion channels that are currently under regulatory review: azimilide dihydrochloride, tedisamil, dronedarone, and vernakalant (RSD-1235). In addition, agents with mechanisms of action that differ from those of existing agents (eg, gap junction modulators) are under review, as is the use of nonantiarrhythmic agents (eg, renin-angiotensin system antagonists, statins, n-3 polyunsaturated fatty acids) to alter the cardiac substrate and suppress AF in some patient subtypes.

Dronedarone for the control of ventricular rate in permanent atrial fibrillation: the Efficacy and safety of dRonedArone for the cOntrol of ventricular rate during atrial fibrillation (ERATO) study

BACKGROUND

Dronedarone is a new multichannel blocker for atrial fibrillation (AF) previously demonstrated to have both rhythm and rate control properties in paroxysmal and persistent AF. The Efficacy and safety of dRonedArone for The cOntrol of ventricular rate during atrial fibrillation (ERATO) trial assessed the efficacy of dronedarone in the control of ventricular rate in patients with permanent AF, when added to standard therapy.

METHODS

In this randomized, double-blind, multinational trial, dronedarone, 400 mg twice a day (n = 85), or matching placebo (n = 89) was administered for 6 months to adult patients with permanent AF, in addition to standard therapy. The primary end point was the change in mean ventricular rate between baseline and day 14, as assessed by 24-hour Holter. Ventricular rate was also assessed during submaximal and maximal exercise.

RESULTS

Dronedarone significantly decreased mean 24-hour ventricular rate. Compared with placebo, the mean treatment effect at day 14 was a reduction of 11.7 beats per minute (beat/min; P < .0001). Comparable reductions were sustained throughout the 6-month trial. During maximal exercise and compared to placebo, there was a mean reduction of 24.5 beat/min (P < .0001), without any reduction in exercise tolerance as measured by maximal exercise duration. The effects of dronedarone were additive to those of other rate-control agents, including beta-blockers, calcium antagonists, and digoxin. Dronedarone was well tolerated, with no organ toxicities or proarrhythmia.

CONCLUSION

In addition to its reported rhythm-targeting and rate-targeting therapeutic actions in paroxysmal and persistent AF, dronedarone improves ventricular rate control in patients with permanent AF. Dronedarone was well tolerated with no evidence of organ toxicities or proarrhythmias in this short-term study.

Increased mortality after dronedarone therapy for severe heart failure

BACKGROUND

Dronedarone is a novel antiarrhythmic drug with electrophysiological properties that are similar to those of amiodarone, but it does not contain iodine and thus does not cause iodine-related adverse reactions. Therefore, it may be of value in the treatment of patients with heart failure.

METHODS

In a multicenter study with a double-blind design, we planned to randomly assign 1000 patients who were hospitalized with symptomatic heart failure and severe left ventricular systolic dysfunction to receive 400 mg of dronedarone twice a day or placebo. The primary end point was the composite of death from any cause or hospitalization for heart failure.

RESULTS

After inclusion of 627 patients (310 in the dronedarone group and 317 in the placebo group), the trial was prematurely terminated for safety reasons, at the recommendation of the data and safety monitoring board, in accordance with the board's predefined rules for termination of the study. During a median follow-up of 2 months, 25 patients in the dronedarone group (8.1%) and 12 patients in the placebo group (3.8%) died (hazard ratio in the dronedarone group, 2.13; 95% confidence interval [CI], 1.07 to 4.25; P=0.03). The excess mortality was predominantly related to worsening of heart failure--10 deaths in the dronedarone group and 2 in the placebo group. The primary end point did not differ significantly between the two groups; there were 53 events in the dronedarone group (17.1%) and 40 events in the placebo group (12.6%) (hazard ratio, 1.38; 95% CI, 0.92 to 2.09; P=0.12). More increases in the creatinine concentration were reported as serious adverse events in the dronedarone group than in the placebo group.

CONCLUSIONS

In patients with severe heart failure and left ventricular systolic dysfunction, treatment with dronedarone was associated with increased early mortality related to the worsening of heart failure. (ClinicalTrials.gov number, NCT00543699.)

Atrial fibrillation and congestive heart failure

Atrial fibrillation (AF) and congestive heart failure (CHF) are common cardiac conditions that frequently coexist. There is a complex interplay between the two conditions, with each increasing the morbidity and mortality associated with the other. The management of AF in patients with CHF requires special care because of the increased risk of antiarrhythmic drug therapy in the group. This report reviews current treatment options and assesses the role of the newer therapies of biventricular pacing for CHF and radiofrequency ablation for AF. It also discusses results of the AF-CHF study, which were reported in November 2007.

Biochemistry and biology of mammalian DNA methyltransferases

DNA methylation is a stable but not irreversible epigenetic signal that silences gene expression. It has a variety of important functions in mammals, including control of gene expression, cellular differentiation and development, preservation of chromosomal integrity, parental imprinting and X-chromosome inactivation. In addition, it has been implicated in brain function and the development of the immune system. Somatic alterations in genomic methylation patterns contribute to the etiology of human cancers and ageing. It is tightly interwoven with the modification of histone tails and other epigenetic signals. Here we review our current understanding of the molecular enzymology of the mammalian DNA methyltransferases Dnmt1, Dnmt3a, Dnmt3b and Dnmt2 and the roles of the enzymes in the above-mentioned biological processes.