Dronedarone

Details

Dronedarone is a non-iodinated benzofuran derivative of amiodarone approved for rhythm and rate control in atrial fibrillation and atrial flutter. It was designed to retain amiodarone's multichannel electrophysiological profile while eliminating iodine-related extracardiac toxicity. Its major clinical advantage over amiodarone is freedom from thyroid, pulmonary, and neurological adverse effects; its major limitation is an absolute contraindication in severe systolic heart failure due to excess mortality in the ANDROMEDA trial. The pivotal ATHENA trial demonstrated a 24.2% relative risk reduction in cardiovascular hospitalisation or death in high-risk AF patients -- the first antiarrhythmic drug to show a morbidity-mortality benefit in this population.

Key Facts

Structure vs Amiodarone

• Dronedarone differs from amiodarone by: (1) removal of both iodine atoms -- eliminating thyroid and pulmonary toxicity; (2) replacement of ethyl groups on the terminal nitrogen with butyl groups; (3) addition of a methanesulfonyl group to the benzofuran ring to reduce lipophilicity, shortening the half-life from amiodarone's 40-55 days to approximately 24 hours. (sources/dronedarone-circ-2009, rating: medium)
• The structural modifications confer a much cleaner extracardiac safety profile but also reduce the drug's sustained antiarrhythmic potency relative to amiodarone (confirmed in DIONYSOS). (sources/dronedarone-circ-2009)

Mechanism of Action

• Multichannel blockade: Dronedarone blocks IKr (rapid delayed rectifier K+), IKs (slow delayed rectifier K+), IK1 (inward rectifier K+), IK-Ach (acetylcholine-gated K+), peak INa, and ICa-L. This broad profile mirrors amiodarone but with two key differences in potency. (sources/dronedarone-circ-2009, rating: medium)
• IK-Ach blockade 100x more potent than amiodarone (IC50 ~10 nmol/L vs ~1 umol/L in guinea pig atrial myocytes). IK-Ach is constitutively active in chronic AF -- dronedarone's potent IK-Ach blockade may be a key mechanism for AF suppression. (sources/dronedarone-circ-2009)
• INa blockade 10x more potent than amiodarone at 3 umol/L in human atrial myocytes (97% vs 41% block). This strong sodium channel inhibition increases the ventricular effective refractory period, which may account for arrhythmic death reduction in ATHENA -- but is also the proposed mechanism for contractility impairment in severe heart failure (ANDROMEDA). (sources/dronedarone-circ-2009)
• Non-competitive beta-adrenergic antagonism via inhibition of adenylate cyclase activity -- contributes to rate control. (sources/dronedarone-circ-2009)
• Acute vs. sustained administration yield opposite APD effects: acute administration abbreviates repolarisation (preclinical models); sustained administration prolongs QTc. (sources/dronedarone-circ-2009)

Pharmacokinetics

• Oral absorption 70-94%; net bioavailability 15% after first-pass metabolism; absorption increases 2-3-fold with food. Steady-state at 400 mg BID reached within 7 days. Terminal half-life ~24 hours. Clearance primarily non-renal. (sources/dronedarone-circ-2009, rating: medium)
• Fixed dose only: 400 mg BID. No dose adjustments for age, sex, race, or renal function have been studied. (sources/dronedarone-circ-2009)

Drug Interactions

• CYP3A4 substrate and moderate inhibitor: Potent CYP3A4 inhibitors (ketoconazole, antifungals, macrolide antibiotics, protease inhibitors) increase dronedarone exposure by up to 25-fold -- co-administration contraindicated. Moderate inhibitors (verapamil, diltiazem) require dose reduction to avoid bradycardia and conduction block. (sources/dronedarone-circ-2009, rating: medium)
• Digoxin: 1.7-2.5-fold increase via P-glycoprotein-mediated renal interaction -- monitor and reduce digoxin dose. (sources/dronedarone-circ-2009)
• Simvastatin: 2-4-fold increase via CYP3A4 inhibition -- risk of statin-induced myopathy. (sources/dronedarone-circ-2009)
• CYP2D6 inhibitor: Modestly increases metoprolol bioavailability; enhanced beta-blockade possible with all co-administered beta-blockers. (sources/dronedarone-circ-2009)
• Serum creatinine elevation: Dronedarone inhibits tubular secretion of creatinine -- apparent creatinine increase does NOT reflect reduced GFR; reversible. (sources/dronedarone-circ-2009)

Clinical Trials

DAFNE -- Dose Finding (Rhythm Control)

• n=270 persistent AF; dronedarone 800/1200/1600 mg daily vs placebo for 6 months. Reverse dose-effect on rhythm control: 800 mg achieved best SR maintenance (35% vs 10% placebo at 6 months; time to AF recurrence 60 vs 5.3 days). Higher doses were superior for rate control during AF recurrence. Dose-dependent QTc prolongation but no TdP. (sources/dronedarone-circ-2009, rating: medium)

EURIDIS and ADONIS -- Phase 3 Rhythm Control

• Pooled n=1237 patients in sinus rhythm; dronedarone 400 mg BID vs placebo for 12 months. Median time to first AF recurrence: 116 days vs 53 days. AF recurrence rate 64.1% vs 75.2%. Post hoc: 27% relative risk reduction in hospitalisation and death. Adverse events comparable to placebo. (sources/dronedarone-circ-2009, rating: medium)

ERATO -- Rate Control in Permanent AF

• n=174 elderly patients with permanent AF on background rate-control therapy; dronedarone 400 mg BID vs placebo for 6 months. Mean ventricular rate reduction: -11.7 bpm at rest and -24.5 bpm during exercise at day 14, sustained over 6 months. No improvement in exercise duration. (sources/dronedarone-circ-2009, rating: medium)

ANDROMEDA -- Severe HF (TERMINATED)

• Planned n=1000; NYHA class III/IV CHF + LVEF <=35%; terminated early after 627 patients. Excess mortality with dronedarone: 8.1% vs 3.8% (HR 2.13). Mechanism proposed: potent INa blockade impairs contractility in the failing myocardium. A retrospective analysis also found higher death in patients withdrawn from ACEi/ARB, though causality is uncertain. (sources/dronedarone-circ-2009, rating: medium)
• ABSOLUTE CONTRAINDICATION established: NYHA III/IV + LVEF <=35%. (sources/dronedarone-circ-2009)

ATHENA -- Pivotal Morbidity/Mortality Trial

• n=4,628 patients with paroxysmal or persistent AF/flutter + >=1 CV risk factor; dronedarone 400 mg BID vs placebo for 12 months. (sources/dronedarone-circ-2009, rating: medium)
• Primary composite endpoint (CV hospitalisation or all-cause death): 24.2% RRR (HR 0.76). First antiarrhythmic to demonstrate morbidity-mortality benefit in an AF population.
• CV death 29% RRR (HR 0.71); CV hospitalisation 26% RRR (HR 0.74); stroke 34% RRR (preserved in patients already on antithrombotics); arrhythmic death HR 0.55.
• All-cause mortality HR 0.84 -- NOT statistically significant. Only 4.4% of ATHENA patients had NYHA III and 3.9% had LVEF <35% -- ATHENA does not rebut ANDROMEDA's HF safety concern.
• Adverse effects: diarrhea 9.7%, nausea 5.3%, bradycardia 3.5%, serum creatinine increase 4.7%, QT prolongation 1.7%. No thyroid or pulmonary toxicity signal.

DIONYSOS -- Comparative Efficacy vs Amiodarone

• n=504 persistent AF; dronedarone 400 mg BID vs amiodarone (600 mg/day x 28 days then 200 mg/day) for minimum 6 months. Primary composite (AF recurrence or premature discontinuation): dronedarone 73.9% vs amiodarone 55.3%. Amiodarone significantly superior in sustained efficacy. Dronedarone had more GI adverse events; amiodarone had more cardiac adverse events (bradycardia, QT prolongation). (sources/dronedarone-circ-2009, rating: medium)

Safety Profile Summary

• Absent in dronedarone (unlike amiodarone): thyroid toxicity, pulmonary toxicity, neurological toxicity, corneal microdeposits, skin photosensitivity/hyperpigmentation.
• Present: GI effects (principal adverse effect -- diarrhea 9.7%, nausea 5.3%); bradycardia; QTc prolongation (dose-dependent, but low TdP risk); serum creatinine elevation (tubular, not GFR); rash.
• Absolute contraindication: NYHA III/IV HF + LVEF <=35% (ANDROMEDA mortality signal). Not for permanent AF in the context of haemodynamic instability.

Contradictions / Open Questions

• PALLAS trial (2011) -- absent from source: The 2009 review predates the PALLAS trial (Connolly et al., NEJM 2011), which showed that dronedarone doubled cardiovascular events (CV death, MI, stroke, or hospitalisation for HF or arrhythmia) in patients with permanent AF + CV risk factors. PALLAS led to a label update restricting dronedarone to paroxysmal or persistent AF only -- not permanent AF. This is the most important post-market safety limitation of this review. (sources/dronedarone-circ-2009)
• ATHENA all-cause mortality non-significant: Despite the impressive composite endpoint reduction, all-cause mortality was not statistically significantly reduced (HR 0.84). The composite benefit was driven primarily by reductions in CV hospitalisation for AF. Whether dronedarone truly reduces mortality in AF patients or primarily reduces hospitalisations remains debated. (sources/dronedarone-circ-2009)
• ANDROMEDA mechanism incompletely characterised: The proposed mechanism for ANDROMEDA mortality (potent INa blockade impairing contractility) is a hypothesis, not confirmed causal data. The confounding role of ACEi/ARB withdrawal in some patients is unresolved. (sources/dronedarone-circ-2009)
• Amiodarone superior in DIONYSOS -- practical positioning unclear: Since amiodarone has greater sustained efficacy in maintaining sinus rhythm and dronedarone has a cleaner extracardiac safety profile, the optimal patient for dronedarone vs amiodarone (beyond the HF contraindication) is not well-defined by these data alone.

Connections

• Related to entities/Amiodarone -- structural parent compound; pharmacological comparator; DIONYSOS direct head-to-head
• Related to entities/Atrial-Fibrillation -- primary indication for dronedarone
• Related to entities/Heart-Failure -- ANDROMEDA absolute contraindication in NYHA III/IV + LVEF <=35%
• Related to concepts/Drug-Induced-Arrhythmia -- QTc prolongation; rare TdP risk
• Related to concepts/Cardiac-Action-Potential -- multichannel blockade
• Related to concepts/Antiarrhythmic-Drugs

Sources

• Related to sources/dronedarone-circ-2009