Dronedarone

In animals, dronedarone prevents atrial fibrillation or restores normal sinus rhythm depending on the model used. It also prevents ventricular tachycardia and ventricular fibrillation in several animal models. These effects most likely result from its electrophysiological properties belonging to all four Vaughan-Williams classes. Dronedarone is a multichannel blocker inhibiting the potassium currents (including IK(Ach), IKur, IKr, IKs) and thus prolonging cardiac action potential and refractory periods (Class III). It also inhibits the sodium currents (Class Ib) and the calcium currents (Class IV). It non-competitively antagonises adrenergic activities (Class II).

Pharmacodynamic properties

In animal models, dronedarone reduces the heart rate. It prolongs Wenckebach cycle length and AH-, PQ-, QT- intervals; with no marked effect or weak increase on QTc-intervals, and with no change in HV- and QRS- intervals. It increases effective refractory periods (ERP) of the atrium, atrio-ventricular node, and ventricular ERP was slightly prolonged with a minimal degree of reverse frequency dependency. Dronedarone decreases arterial blood pressure and myocardial contractility (dP/dt max) with no change in left ventricular ejection fraction and reduces myocardial oxygen consumption. Dronedarone has vasodilatory properties, in coronary arteries (related to the activation of the nitric oxide pathway) and in peripheral arteries. Dronedarone displays indirect antiadrenergic effects and partial antagonism to adrenergic stimulation. It reduces alpha-adrenergic blood pressure response to epinephrine and beta1 and beta2 responses to isoproterenol.

Absorption

Following oral administration in fed condition, dronedarone is well absorbed (at least 70%). However due to presystemic first pass metabolism, the absolute bioavailability of dronedarone (given with food) is 15%. Concomitant intake of food increases dronedarone bioavailability by on average 2- to 4-fold. After oral administration in fed conditions, peak plasma concentrations of dronedarone and the main circulating active metabolite (N-debutyl metabolite) are reached within 3 to 6 hours. After repeated administration of 400 mg twice daily, steady state is reached within 4 to 8 days of treatment and the mean accumulation ratio for dronedarone ranges from 2.6 to 4.5. The steady state mean dronedarone C_max is 84-147 ng/ml and the exposure of the main N-debutyl metabolite is similar to that of the parent compound. The pharmacokinetics of dronedarone and its N-debutyl metabolite both deviate moderately from dose proportionality: a 2-fold increase in dose results in an approximate 2.5- to 3.0-fold increase with respect to C_max and AUC.

Distribution

The in vitro plasma protein binding of dronedarone and its N-debutyl metabolite is 99.7% and 98.5% respectively and is not saturable. Both compounds bind mainly to albumin. After intravenous (IV) administration the volume of distribution at steady state (V_ss) ranges from 1,200 to 1,400 L.

Biotransformation

Dronedarone is extensively metabolised, mainly by CYP 3A4. The major metabolic pathway includes N-debutylation to form the main circulating active metabolite followed by oxidation, oxidative deamination to form the inactive propanoic acid metabolite, followed by oxidation, and direct oxidation. Monoamine Oxidases contribute partially to the metabolism of the active metabolite of dronedarone. The N-debutyl metabolite exhibits pharmacodynamic activity but is 3 to 10-times less potent than dronedarone. This metabolite contributes to the pharmacological activity of dronedarone in humans.

Elimination

After oral administration, approximately 6% of the labelled dose is excreted in urine mainly as metabolites (no unchanged compound excreted in urine) and 84% are excreted in faeces mainly as metabolites. After intravenous administration the plasma clearance of dronedarone ranges from 130 to 150 L/h. The terminal elimination half-life of dronedarone is around 25-30 hours and that of its N-debutyl metabolite around 20-25 hours. In patients, dronedarone and its metabolite are completely eliminated from the plasma within 2 weeks after the end of a 400 mg twice daily-treatment.

Special populations

The pharmacokinetics of dronedarone in patients with AF is consistent with that in healthy subjects. Gender, age and weight are factors that influence the pharmacokinetics of dronedarone. Each of these factors has a limited influence on dronedarone.

Gender

In female patients, dronedarone exposures and its N-debutyl metabolite exposure are on average 1.3- to 1.9-fold higher as compared to male patients.

Elderly

Of the total number of subjects in clinical studies of dronedarone, 73% were 65 years of age and over and 34% were 75 years of age and over. In patients aged 65 years of age and over, dronedarone exposures are 23% higher in comparison with patients aged below 65 years of age.

Hepatic impairment

In subjects with moderate hepatic impairment, dronedarone unbound exposure is increased by 2-fold. That of the active metabolite is decreased by 47%. The effect of severe hepatic impairment on the pharmacokinetics of dronedarone was not assessed.

Renal impairment

The effect of renal impairment on dronedarone pharmacokinetics has not been evaluated in a specific study. Renal impairment is not expected to modify the pharmacokinetics of dronedarone because no unchanged compound was excreted in urine and only approximately 6% of the dose was excreted in urine as metabolites.

Dronedarone had no genotoxic effects, based on one in vivo micronucleus test in mice and four in vitro tests.

In 2-year oral carcinogenicity studies, the highest dronedarone dose administered for 24 months was 70 mg/kg/day in rats and 300 mg/kg/day in mice.

Observations were increased incidence of mammary gland tumors in female mice, histiocytic sarcomas in mice and hemangiomas at the mesenteric lymph node level in rats, all at the highest tested dose only (corresponding to an exposure of 5 to 10 times that of the human therapeutic dose).

Hemangiomas are not precancerous changes and do not transform into malignant hemangiosarcomas in either animals or man. None of these observations was considered relevant for humans.

In chronic toxicity studies, slight and reversible phospholipidosis (accumulation of foamy macrophages) was observed in mesenteric lymph nodes mainly in the rat. This effect is considered specific to this species and not relevant to humans.

Dronedarone caused marked effects on embryo-foetal development at high doses in rats, such as increased post-implantation losses, reduced foetal and placental weights, and external, visceral and skeletal malformations.