Interaction of the antiarrhythmic agents SR 33589 and amiodarone with the beta-adrenoceptor and adenylate cyclase in rat heart

Exploring the interplay between extracellular pH and Dronedarone's pharmacological effects on cardiac function

Dronedarone (DRN) is a clinically used drug to mitigate arrhythmias with multichannel block properties, including the sodium channel Nav1.5. Extracellular acidification is known to change the pharmacological properties of several antiarrhythmic drugs. Here, we explore how modification in extracellular pH (pHe) shapes the pharmacological profile of DRN upon Nav1.5 sodium current (INa) and in the ex vivo heart preparation. Embryonic human kidney cells (HEK293T/17) were used to transiently express the human isoform of Nav1.5 α-subunit. Patch-Clamp technique was employed to study INa. Neurotoxin-II (ATX-II) was used to induce the late sodium current (INaLate). Additionally, ex vivo Wistar male rat preparations in the Langendorff system were utilized to study electrocardiogram (ECG) waves. DRN preferentially binds to the closed state inactivation mode of Nav1.5 at pHe 7.0. The recovery from INa inactivation was delayed in the presence of DRN in both pHe 7.0 and 7.4, and the use-dependent properties were distinct at pHe 7.0 and 7.4. However, the potency of DRN upon the peak INa, the voltage dependence for activation, and the steady-state inactivation curves were not altered in both pHe tested. Also, the pHe did not change the ability of DRN to block INaLate. Lastly, DRN in a concentration and pH dependent manner modulated the QRS complex, QT and RR interval in clinically relevant concentration. Thus, the pharmacological properties of DRN upon Nav1.5 and ex vivo heart preparation partially depend on the pHe. The pHe changed the biological effect of DRN in the heart electrical function in relevant clinical concentration.

Multitargeting nature of muscarinic orthosteric agonists and antagonists

Muscarinic receptors (mAChRs) are typical members of the G protein-coupled receptor (GPCR) family and exist in five subtypes from M1 to M5. Muscarinic receptor subtypes do not sufficiently differ in affinity to orthosteric antagonists or agonists; therefore, the analysis of receptor subtypes is complicated, and misinterpretations can occur. Usually, when researchers mainly specialized in CNS and peripheral functions aim to study mAChR involvement in behavior, learning, spinal locomotor networks, biological rhythms, cardiovascular physiology, bronchoconstriction, gastrointestinal tract functions, schizophrenia, and Parkinson's disease, they use orthosteric ligands and they do not use allosteric ligands. Moreover, they usually rely on manufacturers' claims that could be misleading. This review aimed to call the attention of researchers not deeply focused on mAChR pharmacology to this fact. Importantly, limited selective binding is not only a property of mAChRs but is a general attribute of most neurotransmitter receptors. In this review, we want to give an overview of the most common off-targets for established mAChR ligands. In this context, an important point is a mention the tremendous knowledge gap on off-targets for novel compounds compared to very well-established ligands. Therefore, we will summarize reported affinities and give an outline of strategies to investigate the subtype's function, thereby avoiding ambiguous results. Despite that, the multitargeting nature of drugs acting also on mAChR could be an advantage when treating such diseases as schizophrenia. Antipsychotics are a perfect example of a multitargeting advantage in treatment. A promising strategy is the use of allosteric ligands, although some of these ligands have also been shown to exhibit limited selectivity. Another new direction in the development of muscarinic selective ligands is functionally selective and biased agonists. The possible selective ligands, usually allosteric, will also be listed. To overcome the limited selectivity of orthosteric ligands, the recommended process is to carefully examine the presence of respective subtypes in specific tissues via knockout studies, carefully apply "specific" agonists/antagonists at appropriate concentrations and then calculate the probability of a specific subtype involvement in specific functions. This could help interested researchers aiming to study the central nervous system functions mediated by the muscarinic receptor.

An exploratory analysis of effects of poyendarone, a deuterated analogue of dronedarone, on the canine model of paroxysmal atrial fibrillation

Poyendarone, a deuterated analogue of dronedarone, is expected to reduce the onset of cardiovascular adverse events of dronedarone, including congestive heart failure and excessive QT-interval prolongation. Since information is still lacking on the anti-atrial fibrillatory property of poyendarone, we assessed it along with effects on the inter-atrial conduction time (IACT) and atrial effective refractory period (AERP) using the canine paroxysmal atrial fibrillation model. Poyendarone hydrochloride (n = 4) and dronedarone hydrochloride (n = 4) in intravenous doses of 0.3 and 3 mg/kg/30 s were cumulatively administered. Poyendarone hardly altered sinoatrial rate, but dronedarone decreased it in a dose-related manner, whereas both drugs slightly but significantly reduced idioventricular rate. Poyendarone shortened duration of burst pacing-induced atrial fibrillation, whereas such abbreviation was not observed by dronedarone. Poyendarone and dronedarone similarly prolonged IACT in a frequency-dependent manner, indicating that their I_Na inhibitory actions may be similar. The high dose of poyendarone prolonged AERP in a reverse frequency-dependent manner, extent of which at basic pacing cycle lengths of 300 and 400 ms was comparable to that of dronedarone. However, the extent at a basic pacing cycle length of 200 ms was tended to be greater in poyendarone than in dronedarone, suggesting greater I_Ks inhibitory action of poyendarone. The deuteration of dronedarone attenuated the inhibition of sinus automaticity and prolonged the AERP with keeping the blood pressure and ventricular rate stable. Thus, poyendarone may have both more potent anti-atrial fibrillatory action and wider cardiovascular safety margin than dronedarone.

How the Deuteration of Dronedarone Can Modify Its Cardiovascular Profile: In Vivo Characterization of Electropharmacological Effects of Poyendarone, a Deuterated Analogue of Dronedarone

Since deuterium replacement has a potential to modulate pharmacodynamics, pharmacokinetics and toxicity, we developed deuterated dronedarone; poyendarone, and assessed its cardiovascular effects. Poyendarone hydrochloride in doses of 0.3 and 3 mg/kg over 30 s was intravenously administered to the halothane-anesthetized dogs (n = 4), which provided peak plasma concentrations of 108 ± 10 and 1120 ± 285 ng/mL, respectively. The 0.3 mg/kg shortened the ventricular repolarization period. The 3 mg/kg transiently increased the heart rate at 5 min but decreased at 45 min, and elevated the total peripheral vascular resistance and left ventricular preload, whereas it reduced the mean blood pressure at 5 min, left ventricular contractility and cardiac output. The transient tachycardic action is considered to be induced by the hypotension-induced, reflex-mediated increase of sympathetic tone. The 3 mg/kg delayed both intra-atrial and intra-ventricular conductions, indicating Na⁺ channel inhibitory action. Moreover, the 3 mg/kg transiently shortened the ventricular repolarization period at 5 min. No significant change was detected in the late repolarization by poyendarone, indicating it might not hardly significantly alter rapidly activating delayed-rectifier K⁺ current (I_Kr). Poyendarone prolonged the atrial effective refractory period greater than the ventricular parameter. When compared with dronedarone, poyendarone showed similar pharmacokinetics of dronedarone, but reduced β-adrenoceptor blocking activity as well as the cardio-suppressive effect. Poyendarone failed to inhibit I_Kr and showed higher atrial selectivity in prolonging the effective refractory period of atrium versus ventricle. Thus, the deuteration may be an effective way to improve the cardiovascular profile of dronedarone. Poyendarone is a promising anti-atrial fibrillatory drug candidate.

Comparative effects of amiodarone and dronedarone treatments on cardiac function in a rabbit model

AIM

The objective of the study was to compare the effects of amiodarone (AM) and dronedarone (DR) on heart rate variability (HRV) and cardiac contractility in a rabbit model.

MATERIALS AND METHODS

A total of 16 male New Zealand white rabbits were divided into two groups, treated either with AM or DR at incremental dosages of 50 mg/kg/day (AM50 and DR50) and 100 mg/kg/day (AM100 and DR100), orally administrated for 7 days. At the end of each period, electrocardiograms were recorded during consciousness and analyzed using the short-term time and frequency domains of HRV. Standard echocardiography and speckle-tracking echocardiography were studied during immobilization with xylazine and ketamine.

RESULTS

The results showed that AM100 and DR100 significantly decreased heart rate, total power, low-frequency component, and low-to-high frequency ratio compared with baselines. Most echocardiogram parameters revealed no significant difference from baselines, except for the global circumferential plane strain rate and time to peak standard deviation of strain, which had statistical significances after treating with AM.

CONCLUSION

Both AM and DR possess negative chronotropy and reduce HRV, which may be explained by their sympathetic suppression and calcium channel blocking activities. Theoretically, both antiarrhythmic drugs may also possess negative inotropy, but only AM is shown to have a negative inotropic effect and reduces cardiac dyssynchrony in this model.

Influence of Amiodarone and Dronedarone on the Force-Interval Dependence of Rat Myocardium

The antiarrhythmic effect of amiodarone and its analogue dronedarone is caused by their direct actions on several cardiomyocyte sarcolemmal ion currents. However, whether their effects are related to intracellular calcium levels is not exactly known. Ca²⁺ cycling refers to the release and reuptake of intracellular Ca²⁺, which induces muscle contraction and relaxation and determines the force-interval dependence. This study aimed to evaluate the influence of amiodarone and dronedarone on the force-interval relationship. Materials and Results. The work was performed on the papillary muscles of the left ventricle of male Wistar rats. Muscle perfusion was performed at 36.5°C with oxygenated Krebs-Henseleit solution with baseline stimulation 0.5 Hz. The postrest test (4-60 s) and the extrasystolic exposure (0.2-1.5 s) were evaluated. Inotropic reaction to the test exposure was evaluated before and after muscle perfusion with solution containing amiodarone (10⁻⁶ M) or dronedarone (10⁻⁶ M) during 10 min. Amiodarone or dronedarone led to decrease of the amplitude of extrasystolic contractions of the papillary muscles. The amplitude of postextrasystolic contractions after short extrasystolic intervals on the background of the drugs was increased. Amiodarone and dronedarone led to increase of the amplitude of postrest contractions. Conclusions. Dronedarone reduces the excitability of cardiomyocyte sarcolemma to a greater extent than amiodarone. Amiodarone and dronedarone are able to increase postextrasystolic and postrest potentiation. The effect of amiodarone on postextrasystolic and postrest potentiation is more pronounced in comparison with dronedarone.

Cardiovascular pharmacology of K2P17.1 (TASK-4, TALK-2) two-pore-domain K+ channels

K_2P17.1 (TASK-4, TALK-2) potassium channels are expressed in the heart and represent potential targets for pharmacological management of atrial and ventricular arrhythmias. Reduced K_2P17.1 expression was found in atria and ventricles of heart failure (HF) patients. Modulation of K_2P17.1 currents by antiarrhythmic compounds has not been comprehensively studied to date. The objective of this study was to investigate acute effects of clinically relevant antiarrhythmic drugs on human K_2P17.1 channels to provide a more complete picture of K_2P17.1 electropharmacology. Whole-cell patch clamp and two-electrode voltage clamp electrophysiology was employed to study human K_2P17.1 channel pharmacology. K_2P17.1 channels expressed in Xenopus laevis oocytes were screened for sensitivity to antiarrhythmic drugs, revealing significant activation by propafenone (+ 296%; 100 μM), quinidine (+ 58%; 100 μM), mexiletine (+ 21%; 100 μM), propranolol (+ 139%; 100 μM), and metoprolol (+ 17%; 100 μM) within 60 min. In addition, the currents were inhibited by amiodarone (- 13%; 100 μM), sotalol (- 10%; 100 μM), verapamil (- 21%; 100 μM), and ranolazine (- 8%; 100 μM). K_2P17.1 channels were not significantly affected by ajmaline and carvedilol. Concentration-dependent K_2P17.1 activation by propafenone was characterized in more detail. The onset of activation was fast, and current-voltage relationships were not modulated by propafenone. K_2P17.1 activation was confirmed in mammalian Chinese hamster ovary cells, revealing 7.8-fold current increase by 100 μM propafenone. Human K_2P17.1 channels were sensitive to multiple antiarrhythmic drugs. Differential pharmacological regulation of repolarizing K_2P17.1 background K⁺ channels may be employed for personalized antiarrhythmic therapy.

Dronedarone attenuates the duration of atrial fibrillation in a dog model of sustained atrial fibrillation

Atrial fibrillation (AF) is a supraventricular arrhythmia that leads to a decrease in cardiac output and impairs cardiac function and quality of life. Dronedarone has an atrial-selective property and has been used for management of AF in humans, but limited information is available in dogs. This study was designed to evaluate efficacy of dronedarone in attenuating the duration of AF in dog model of sustained AF. Six beagle dogs were anesthetized with isoflurane and instrumented to measure atrial action potential duration (aAPD) and atrial effective refractory period (AERP). Then AF was induced by rapid right atrial pacing (20 V, 40 Hz) simultaneously with infusion of phenylephrine (2 µg/kg/min, intravenously) for 20 min. The duration of sustained AF was recorded, and the animals were allowed to recover. Dronedarone was given at a dose of 20 mg/kg, BID, orally for 7 days. On the last day, the dogs were anesthetized again to record aAPD and AERP, and AF was induced with the same procedure as described above. The results showed that after dronedarone administration the aAPD was lengthened significantly from 76.4 ± 4.2 ms to 91.2 ± 3.9 ms (P<0.05) and AERP was prolonged significantly from 97.5 ± 2.8 ms to 120 ± 4.8 ms (P<0.05). The duration of sustained AF was also significantly attenuated after receipt of dronedarone (P<0.05). It can be suggested that oral dronedarone attenuates the duration of sustained AF in a dog model of AF by extending the AERP more than the aAPD, causing post-repolarization refractoriness. Hence, dronedarone may be useful for management of AF in dogs.

Intracellular Calcium Mobilization in Response to Ion Channel Regulators via a Calcium-Induced Calcium Release Mechanism

Free intracellular calcium ([Ca²⁺]_i), in addition to being an important second messenger, is a key regulator of many cellular processes including cell membrane potential, proliferation, and apoptosis. In many cases, the mobilization of [Ca²⁺]_i is controlled by intracellular store activation and calcium influx. We have investigated the effect of several ion channel modulators, which have been used to treat a range of human diseases, on [Ca²⁺]_i release, by ratiometric calcium imaging. We show that six such modulators [amiodarone (Ami), dofetilide, furosemide (Fur), minoxidil (Min), loxapine (Lox), and Nicorandil] initiate release of [Ca²⁺]_i in prostate and breast cancer cell lines, PC3 and MCF7, respectively. Whole-cell currents in PC3 cells were inhibited by the compounds tested in patch-clamp experiments in a concentration-dependent manner. In all cases [Ca²⁺]_i was increased by modulator concentrations comparable to those used clinically. The increase in [Ca²⁺]_i in response to Ami, Fur, Lox, and Min was reduced significantly (P < 0.01) when the external calcium was reduced to nM concentration by chelation with EGTA. The data suggest that many ion channel regulators mobilize [Ca²⁺]_i. We suggest a mechanism whereby calcium-induced calcium release is implicated; such a mechanism may be important for understanding the action of these compounds.

The effect of long-term amiodarone administration on myocardial fibrosis and evolution of left ventricular remodeling in a porcine model of ischemic cardiomyopathy

Amiodarone is effective in suppressing arrhythmias in heart failure patients. We investigated the effect of long-term amiodarone administration on myocardial fibrosis and left ventricular (LV) remodeling in a porcine model of ischemic cardiomyopathy. Eighteen infarcted farm pigs were randomized to receive long-term amiodarone administration for 3 months (n = 9) or conventional follow-up (n = 9). Evolution of LV remodeling over 3 months post-myocardial infarction was examined at tissue level (myocyte size, myocardial fibrosis and vascular density assessed by whole-field digital histopathology), organ level (LV structure and function assessed by echocardiography), and systemic level (BNP and MMP-9 levels). Long-term administration of the standard anti-arrhythmic doses of amiodarone was not associated with adverse effects on myocardial fibrosis and other features of adverse cardiac remodeling. This favorable safety profile suggests that long-term anti-arrhythmic therapy with amiodarone warrants further clinical investigation in the subpopulation of heart failure patients with significantly increased burden of arrhythmias.

Acute effects of intravenous dronedarone on electrocardiograms, hemodynamics and cardiac functions in anesthetized dogs

Dronedarone is a class III antiarrhythmic that has been used for management of atrial fibrillation in humans, but limited information was found in dogs. The objective of this study was to determine the acute effects of escalating concentrations of dronedarone on electrocardiograms (ECG), hemodynamics and cardiac mechanics in healthy dogs. A total of 7 beagle dogs were anesthetized with isoflurane and instrumented to obtain lead II ECG, pressures at ascending aorta, right atrium, pulmonary artery and left ventricle, and left ventricular pressure-volume relationship. Five dogs were given vehicle and followed by escalating doses of dronedarone (0.5, 1.0 and 2.5 mg/kg, 15 min for each dose), and two dogs were used as a vehicle-treated control. All parameters were measured at 15 min after the end of each dose. The results showed that all parameters in vehicle-treated dogs were unaltered. Dronedarone at 2.5 mg/kg significantly lengthened PQ interval (P<0.01), reduced cardiac output (P<0.01) and increased systemic vascular resistance (P<0.01). Dronedarone produced negative inotropy assessed by significantly lowered end-systolic pressure-volume relationship, preload recruitable stroke work, contractility index and dP/dtmax. It also impaired diastolic function by significantly increased end-diastolic pressure-volume relationship, tau and dP/dtmin. These results suggested that acute effects of dronedarone produced negative dromotropy, inotropy and lusitropy in anesthetized dogs. Care should be taken when given dronedarone to dogs, especially when the patients have impaired cardiac function.

Benefit-risk assessment of dronedarone in the treatment of atrial fibrillation

Rhythm control in atrial fibrillation (AF) can be achieved using pharmacological therapy. Amiodarone is the most efficacious anti-arrhythmic agent; however, its use is limited due to an unfavourable safety profile, including pro-arrhythmia, thyroid, liver, skin and pulmonary complications. Dronedarone, which is structurally similar to amiodarone, was developed to try and achieve a favourable balance of efficacy and risk. Dronedarone has been evaluated in several large clinical trials, which have shown reduced mortality and hospitalization rates in patients with non-permanent AF. In patients with permanent AF and/or heart failure, dronedarone has been shown to cause increased mortality and morbidity and should not be used in these groups. Compared with amiodarone, dronedarone has fewer toxic effects (thyroid, skin, pulmonary) and, although less efficacious, may be used as first-line therapy for maintenance of sinus rhythm in patients with non-permanent AF. Clinicians must be vigilant in monitoring their patients to ensure they do not develop permanent AF or heart failure.

Dronedarone: an overview

Atrial fibrillation (AF) is the most common arrhythmia encountered in clinical practice. Until recently, a rhythm control strategy for AF has been limited by drug toxicity and side-effects, and landmark AF trials have shown that such a strategy is not superior to a rate control one. New antiarrhythmic drugs, free of undesired effects, would enhance the rhythm control strategy, with the possibility of sinus rhythm restoration and maintenance. One of the promising drugs recently approved for clinical use is dronedarone. This drug has amiodarone-like antiarrhythmic and electrophysiological properties, despite it having a modified structure and lacking an iodine moiety. Thus, dronedarone lacks amiodarone's organ toxicity (including adverse thyroid and pulmonary effects). The efficacy of dronedarone has been investigated in several clinical trials, proving its effect in the prevention of AF recurrence, rate control in paroxysmal/persistent and permanent AF, reduction of cardiovascular hospitalization or death from any cause, and others. Indirect comparisons with amiodarone, as well as one head-to-head study of the two drugs, indicate that the relative safety of dronedarone may be at a cost of its lower antiarrhythmic efficacy compared with amiodarone.

Dronedarone in high-risk permanent atrial fibrillation

BACKGROUND

Dronedarone restores sinus rhythm and reduces hospitalization or death in intermittent atrial fibrillation. It also lowers heart rate and blood pressure and has antiadrenergic and potential ventricular antiarrhythmic effects. We hypothesized that dronedarone would reduce major vascular events in high-risk permanent atrial fibrillation.

METHODS

We assigned patients who were at least 65 years of age with at least a 6-month history of permanent atrial fibrillation and risk factors for major vascular events to receive dronedarone or placebo. The first coprimary outcome was stroke, myocardial infarction, systemic embolism, or death from cardiovascular causes. The second coprimary outcome was unplanned hospitalization for a cardiovascular cause or death.

RESULTS

After the enrollment of 3236 patients, the study was stopped for safety reasons. The first coprimary outcome occurred in 43 patients receiving dronedarone and 19 receiving placebo (hazard ratio, 2.29; 95% confidence interval [CI], 1.34 to 3.94; P=0.002). There were 21 deaths from cardiovascular causes in the dronedarone group and 10 in the placebo group (hazard ratio, 2.11; 95% CI, 1.00 to 4.49; P=0.046), including death from arrhythmia in 13 patients and 4 patients, respectively (hazard ratio, 3.26; 95% CI, 1.06 to 10.00; P=0.03). Stroke occurred in 23 patients in the dronedarone group and 10 in the placebo group (hazard ratio, 2.32; 95% CI, 1.11 to 4.88; P=0.02). Hospitalization for heart failure occurred in 43 patients in the dronedarone group and 24 in the placebo group (hazard ratio, 1.81; 95% CI, 1.10 to 2.99; P=0.02).

CONCLUSIONS

Dronedarone increased rates of heart failure, stroke, and death from cardiovascular causes in patients with permanent atrial fibrillation who were at risk for major vascular events. Our data show that this drug should not be used in such patients. (Funded by Sanofi-Aventis; PALLAS ClinicalTrials.gov number, NCT01151137.).

Dronedarone: an alternative to amiodarone?

OBJECTIVE

To review the safety and efficacy of the newly approved, mixed-activity antiarrhythmic dronedarone (classes I-IV) versus its parent compound comparator, amiodarone (class III, with mixed activity).

DATA SOURCES

A MEDLINE/PUBMED (January 1966 to March 2010) and International Pharmaceutical Abstract (January 1975 to March 2010) search of English language papers in addition to a bibliographic search of retrieved papers.

STUDY SELECTION

All human studies of dronedarone, alone or in combination with amiodarone, were reviewed.

DATA SYNTHESIS

Approved in July 2009, dronedarone is a new antiarrhythmic agent indicated to reduce the risk of hospitalization for cardiac events in patients with paroxysmal or persistent atrial fibrillation or atrial flutter. Dronedarone has been viewed as a potential therapeutic alternative for amiodarone because of a lower risk for pulmonary, thyroid, and dermatologic adverse effects. Compared with amiodarone, dronedarone has poor bioavailability and a shorter terminal disposition half-life, which dictates a twice-daily dosing regimen. Furthermore, dronedarone failed to demonstrate superiority over amiodarone with respect to recurrence of atrial fibrillation in a comparative efficacy analysis. Dronedarone therapy is more costly and increases overall tablet burden. No dosage adjustments are required with dronedarone for renal impairment. Use of dronedarone is contraindicated in the presence of severe hepatic impairment. No serious organ-related toxicities (i.e., thyroid and pulmonary system) have been reported with use of dronedarone.

CONCLUSION

Dronedarone as a niche drug may be a reasonable theoretical alternative for patients who cannot tolerate amiodarone or have underlying comorbidities that contraindicate amiodarone use (e.g., pulmonary, thyroid disease). However, dronedarone has not been studied in the vast majority of indications and patient populations in which amiodarone has been studied.

Dronedarone: evidence supporting its therapeutic use in the treatment of atrial fibrillation

Introduction:

Dronedarone, a benzofuran derivative with a structure similar to amiodarone, has been developed as a potential therapy for patients with atrial fibrillation.

Aim:

To review the published evidence regarding the efficacy and safety of dronedarone use in patients with atrial fibrillation.

Evidence review:

Available evidence suggests that dronedarone 400 mg orally twice daily can lengthen the time to and decrease the overall recurrence of atrial fibrillation compared with placebo. Dronedarone may reduce risk of mortality and cardiovascular hospitalization. Patients with atrial fibrillation receiving dronedarone had improved ventricular rate control compared with patients receiving placebo. Dronedarone is associated with few serious adverse events except, notably, in patients with decompensated heart failure.

Place in therapy:

Dronedarone may have a role in rate and rhythm control for patients with atrial fibrillation. Dronedarone can reduce unique, but potentially serious, end points in patients with atrial fibrillation. Despite this, the exact role of dronedarone in the management of patients with atrial fibrillation continues to emerge. It remains uncertain if dronedarone should be considered a primary treatment strategy for atrial fibrillation. Dronedarone should not be administered to patients with decompensated heart failure.

Conclusion:

Dronedarone is a unique drug that may serve a key role to treat patients with atrial fibrillation.

Pharmacokinetics/Pharmacodynamics of Antiarrhythmic Drugs

This article describes the pharmacology of antiarrhythmic medications. Although these medications are broadly considered in terms of their blockade of either sodium or potassium channels, they act by a variety of pharmacodynamic mechanisms. Elimination may be via hepatic metabolism or renal mechanisms, or a combination. In particular, interactions between antiarrhythmic medications and other drugs that interfere with hepatic metabolism by P450 enzymes is a source for toxicity.

Significant sirolimus and dronedarone interaction in a kidney transplant recipient

OBJECTIVE

To report the potential clinically significant pharmacokinetic interaction between sirolimus and dronedarone.

CASE SUMMARY

A 67-year-old man status post-kidney transplant in 2004 was maintained on an immunosuppressive regimen consisting of sirolimus, mycophenolate mofetil, and prednisone. He had been maintained for more than 1 year on a stable dose of sirolimus (5 mg/day), with concentrations ranging between 5 and 13.5 ng/mL. The patient was admitted to the hospital with a complaint of bloody diarrhea; shortly after admission, he developed atrial fibrillation for which dronedarone 400 mg twice daily was initiated. Sirolimus concentrations obtained 3 days after initiation of dronedarone revealed a trough concentration that was increased by more than 3-fold (38.6 ng/mL) from his baseline trough concentration. After sirolimus was held for 6 days, the trough concentration was 7.8 ng/mL. The dosage was reduced to 1 mg/day; there was no need for further adjustment.

DISCUSSION

While the potential for an interaction between sirolimus and dronedarone is listed in the package insert of dronedarone, there are no documented reports of this interaction in the peer-reviewed literature. Since sirolimus is a narrow therapeutic index medication, information about the severity and magnitude of the interaction with dronedarone may help clinicians avoid therapeutic misadventures when this combination is employed. Our case clearly demonstrates a significant pharmacokinetic interaction between sirolimus and dronedarone. The Horn Drug Interaction Probability Scale indicates that the occurrence of an interaction between sirolimus and dronedarone in our case is probable.

CONCLUSIONS

Due to the potential for sirolimus toxicity and excessive immunosuppression, the concurrent use of dronedarone and sirolimus should be avoided when possible. If concurrent administration cannot be avoided, we suggest close monitoring and a 50-75% dose reduction of sirolimus prior to dronedarone initiation.

Impact of dronedarone in atrial fibrillation and flutter on stroke reduction

Background:

Dronedarone has been developed for treatment of atrial fibrillation (AF) or atrial flutter (AFL). It is an amiodarone analogue but noniodinized and without the same adverse effects as amiodarone.

Objective and methods:

This is a review of 7 studies (DAFNE, ADONIS, EURIDIS, ATHENA, ANDROMEDA, ERATO and DIONYSOS) on dronedarone focusing on efficacy, safety and prevention of stroke. There was a dose-finding study (DAFNE), 3 studies focusing on maintenance of sinus rhythm (ADONIS, EURIDIS and DIONYSOS), 1 study focusing on rate control (ERATO) and 2 studies investigating mortality and morbidity (ANDROMEDA and ATHENA).

Results:

The target dose for dronedarone was established in the DAFNE study to be 400 mg twice daily. Both EURIDIS and ADONIS studies demonstrated that dronedarone was superior to placebo for maintaining sinus rhythm. However, DIONYSOS found that dronedarone is less efficient at maintaining sinus rhythm than amiodarone. ERATO concluded that dronedarone reduces ventricular rate in patients with chronic AF. The ANDROMEDA study in patients with severe heart failure was discontinued because of increased mortality in dronedarone group. Dronedarone reduced cardiovascular hospitalizations and mortality in patients with AF or AFL in the ATHENA trial. Secondly, according to a post hoc analysis a significant reduction in stroke was observed (annual rate 1.2% on dronedarone vs 1.8% on placebo, respectively [hazard ratio 0.66, confidence interval 0.46 to 0.96, P = 0.027]). In total, 54 cases of stroke occurred in 3439 patients (crude rate 1.6%) receiving dronedarone compared to 76 strokes in 3048 patients on placebo (crude rate 2.5%), respectively.

Conclusion:

Dronedarone can be used for maintenance of sinus rhythm and can reduce stroke in patients with AF who receive usual care, which includes antithrombotic therapy and heart rate control.

Dronedarone

Amiodarone is the most effective antiarrhythmic drug for maintaining sinus rhythm for patients with atrial fibrillation. Extra-cardiac side effects have been a limiting factor, especially during chronic use, and may offset its benefits. Dronedarone is a noniodinated benzofuran derivative of amiodarone that has been developed for the treatment of atrial fibrillation and atrial flutter. Similar to amiodarone, dronedarone is a potent blocker of multiple ion currents, including the rapidly activating delayed-rectifier potassium current, the slowly activating delayed-rectifier potassium current, the inward rectifier potassium current, the acetylcholine activated potassium current, peak sodium current, and L-type calcium current, and exhibits antiadrenergic effects. It has been studied for maintenance of sinus rhythm and control of ventricular response during episodes of atrial fibrillation. Dronedarone reduces mortality and morbidity in patients with high-risk atrial fibrillation, but may be unsafe in those with severe heart failure. This article will review evidence of safety and effectiveness of dronedarone in patients with atrial fibrillation.

[Dronedarone: the new antiarrythmic agent?]

Dronedarone is recommended as the successor drug to amiodarone because a faster onset of effects and less side effects are to be expected. This review describes the pharmacological properties of this multi-channel blocker and summarizes the results from recent studies proving successful antiarrhythmic therapy using dronedarone in patients with atrial fibrillation.

Interaction with the hERG channel and cytotoxicity of amiodarone and amiodarone analogues

BACKGROUND AND PURPOSE

Amiodarone (2-n-butyl-3-[3,5 diiodo-4-diethylaminoethoxybenzoyl]-benzofuran, B2-O-CH(2)CH(2)-N-diethyl) is an effective class III antiarrhythmic drug demonstrating potentially life-threatening organ toxicity. The principal aim of the study was to find amiodarone analogues that retained human ether-a-go-go-related protein (hERG) channel inhibition but with reduced cytotoxicity.

EXPERIMENTAL APPROACH

We synthesized amiodarone analogues with or without a positively ionizable nitrogen in the phenolic side chain. The cytotoxic properties of the compounds were evaluated using HepG2 (a hepatocyte cell line) and A549 cells (a pneumocyte line). Interactions of all compounds with the hERG channel were measured using pharmacological and in silico methods.

KEY RESULTS

Compared with amiodarone, which displayed only a weak cytotoxicity, the mono- and bis-desethylated metabolites, the further degraded alcohol (B2-O-CH(2)-CH(2)-OH), the corresponding acid (B2-O-CH(2)-COOH) and, finally, the newly synthesized B2-O-CH(2)-CH(2)-N-pyrrolidine were equally or more toxic. Conversely, structural analogues such as the B2-O-CH(2)-CH(2)-N-diisopropyl and the B2-O-CH(2)-CH(2)-N-piperidine were significantly less toxic than amiodarone. Cytotoxicity was associated with a drop in the mitochondrial membrane potential, suggesting mitochondrial involvement. Pharmacological and in silico investigations concerning the interactions of these compounds with the hERG channel revealed that compounds carrying a basic nitrogen in the side chain display a much higher affinity than those lacking such a group. Specifically, B2-O-CH(2)-CH(2)-N-piperidine and B2-O-CH(2)-CH(2)-N-pyrrolidine revealed a higher affinity towards hERG channels than amiodarone.

CONCLUSIONS AND IMPLICATIONS

Amiodarone analogues with better hERG channel inhibition and cytotoxicity profiles than the parent compound have been identified, demonstrating that cytotoxicity and hERG channel interaction are mechanistically distinct and separable properties of the compounds.

In vitro effects of acute amiodarone and dronedarone on epicardial, endocardial, and M cells of the canine ventricle

Amiodarone (AM) is an antiarrhythmic agent widely used in the treatment of ventricular and supraventricular arrhythmias. Dronedarone (DR) is a new compound with a pharmacological profile similar to that of AM, but iodine free. We previously demonstrated that chronic AM treatment reduces transmural dispersion of repolarization (TDR) in the canine heart. We used standard microelectrode technique to evaluate the effects of acute AM (100 microM) and DR (30 microM) on epicardial (EPI), endocardial (ENDO), and M region tissues obtained from the left ventricular wall of the canine heart. Amiodarone (100 microM, 120 min of exposure) produced little change in the action potential duration of ENDO and EPI tissues, but it shortened the action potential of M cells, especially at slow rates, leading to a decrease in TDR. Similar results were observed with DR. Acute AM (100 microM) and DR (30 microM) eliminated d-sotalol-induced early afterdepolarizations (EADs) and triggered activity in 3 of 3 and 2 of 6 M cell preparations, respectively. The reduction of TDR and the elimination of EAD-induced triggered activity differentiates AM and DR from other class III agents. These effects may explain the efficacy and low arrhythmogenicity of acute AM and suggest a potential safe use of DR as an antiarrhythmic agent.

Acute in vitro effects of dronedarone, an iodine-free derivative, and amiodarone, on the rabbit sinoatrial node automaticity: a comparative study

Amiodarone is a potent antiarrhythmic drug commonly used in the treatment of supraventricular and ventricular arrhythmias. Dronedarone is a recently developed iodine-free compound (Sanofi Recherche), structurally related to amiodarone. Amiodarone and dronedarone have shown similar long-term effects on sinoatrial node automaticity in vivo and in vitro in the rabbit heart. In the present study, we used a microelectrode technique to compare the acute in vitro electrophysiologic effects of amiodarone (100 microM) and dronedarone (100 microM) on the rabbit sinus node. Like amiodarone, dronedarone induces a marked reduction in sinus node automaticity, evidenced by decreases in spontaneous beating rate, action potential amplitude, and slope of phase 4 depolarization. Isoproterenol dose-dependently increases sinus node automaticity in the presence of either amiodarone or dronedarone. The data suggest that dronedarone may be a useful antiarrhythmic alternative to amiodarone in the treatment of supraventricular arrhythmias.

Negative inotropic and lusitropic effects of intravenous amiodarone in conscious rats

1. The acute effect of amiodarone on haemodynamics (mean arterial pressure and heart rate) and ventricular function (+dP/dt(max) and -dP/dt(max)) was investigated in conscious rats. In addition, the effects of amiodarone on dobutamine stress were determined. 2. Catheters were inserted in rats into the left ventricle and femoral artery and vein. Three groups of rats received 25 or 50 mg/kg, i.v., amiodarone or vehicle (a 1:1:8 mixture of Tween 80:99.5% ethanol:distilled water), followed by dobutamine (10 microg/kg). 3. The hypotensive effect of 50 mg/kg amiodarone was combined with marked bradycardia and attenuation of +dP/dt(max) and -dP/dt(max). A slight, but significant, hypotension was caused by 25 mg/kg amiodarone, without affecting heart rate, +dP/dt(max) and -dP/dt(max). However, although both doses of amiodarone attenuated the tachycardia caused by dobutamine, neither 25 nor 50 mg/kg amiodarone affected the increase in mean arterial pressure or the enhanced response of +dP/dt(max) and -dP/dt(max). 4. In conclusion, amiodarone caused hypotension, bradycardia, negative inotropic (+dP/dt(max)) and lusitropic (-dP/dt(max)) effects in conscious rats. In addition, amiodarone attenuated the tachycardia without affecting the hypertensive, contractile (+dP/dt(max)) and lusitropic (-dP/dt(max)) responses to dobutamine stress.

Pharmacologic targets for atrial fibrillation

Despite advances in treatment, atrial fibrillation (AF) remains the most common arrhythmia in humans. Antiarrhythmic drug therapy continues to be a cornerstone of AF treatment, even in light of emerging non-pharmacologic therapies. Conventional antiarrhythmic drugs target cardiac ion channels and are often associated with modest AF suppression and the risk of ventricular proarrhythmia. Ongoing drug development has focused on targeting atrial-specific ion channels as well as novel non-ionic targets. Targeting non-ionic mechanisms may also provide new drugs directed towards the underlying mechanisms responsible for AF and possibly greater antiarrhythmic potency. Agents that act against these new targets may offer improved safety and efficacy in AF treatment.

A review of the investigational antiarrhythmic agent dronedarone

Arrhythmias are a major cause of morbidity and mortality, and atrial fibrillation is the most widespread disorder of cardiac rhythm. Amiodarone is an effective antiarrhythmic agent that has been in clinical use for about 20 years. It is effective for multiple types of arrhythmias, including atrial fibrillation, and has a low incidence of cardiac adverse events, including Torsade de Pointes. It has many noncardiac adverse effects that are serious and limit its long-term use. Dronedarone is an investigational antiarrhythmic agent that is designed to have similar cardiac effects to amiodarone but with fewer adverse effects. This review presents some of the animal and human studies that evaluate the effects of dronedarone.

Dose-dependent effects of oral dronedarone on the circadian variation of RR and QT intervals in healthy subjects: implications for antiarrhythmic actions

Dronedarone, a non-iodinated benzofuran derivative, was developed as a potentially less toxic alternative to amiodarone. This study describes Holter data of dronedarone in humans. Five groups of healthy subjects were given 1 of 5 oral doses of dronedarone in a twice-daily regimen or placebo. Holter recordings of circadian rhythmicity of RR and QT intervals were evaluated. Dronedarone prolonged RR and QT intervals as a function of dose, without effect on circadian patterns. The relative prolongation of QT, QTc, and RR by dronedarone was significant. The QTc interval did not exhibit a clearly recognizable circadian pattern, suggesting that the circadian pattern of the QT interval was mostly a reflection of circadian changes in the RR interval in the study population. Dronedarone resembled amiodarone in class III and sympatholytic effects, indicating its potential as a unique antiarrhythmic compound seemingly devoid of the side effects mediated by iodine in amiodarone.

Dronedarone

Dronedarone, a potassium channel antagonist, is chemically related to amio-darone. It is being developed by sanofi-aventis as a class III antiarrhythmic agent for the treatment of atrial fibrillation and atrial flutter in the US and Europe. Dronedarone has a favourable benefit/risk ratio, with the absence of any proarrhythmic effects. Sanofi merged with Synthélabo to form Sanofi-Synthélabo in 1999. In August 2004, Sanofi-Synthelabo merged with Aventis to form sanofi-aventis. The ATHENA trial is a multinational, randomised, double-blind trial evaluating the effects of dronedarone (400mg bid) compared with placebo, over a minimum 12-month follow-up period, in patients with atrial fibrillation or flutter. The trial is investigating the efficacy of dronedarone in preventing cardiovascular hospitalisations or death from any cause. Enrolment was extended to 4300 patients in order to attain the planned rate of adverse events; patient recruitment is ongoing.Previously, sanofi-aventis completed two pivotal phase III trials in atrial fibrillation. The trials, EURIDIS (EURopean trial In atrial fibrillation or flutter patients for the maintenance of Sinus rhythm) and ADONIS (American-Australasian trial with DronedarONe In atrial fibrillation or flutter patients for the maintenance of Sinus rhythm), involved 1237 patients who were in sinus rhythm at the time of randomisation. Results showed dronedarone to have anti-arrhythmic effects and a favourable benefit/risk ratio, with the absence of any proarrhythmic effect.Another trial, ERATO (Efficacy and safety of dronedARone for The cOntrol of ventricular rate), took place in 35 centres across nine European countries assessing dronedarone in 174 patients with permanent atrial fibrillation. Dronedarone was in phase II trials in Japan for the treatment of atrial fibrillation; however, no recent developments have been reported.

Dronedarone: An Emerging Agent with Rhythm- and Rate-Controlling Effects

Of current antiarrhythmic agents, amiodarone is among the most effective with the additional advantage of having little proarrhythmic potential. However, it can cause potentially serious extracardiac side effects, stimulating the search for safer derivatives. Dronedarone, a new antiarrhythmic drug that is structurally related to amiodarone, lacks an iodine moiety and, thus, amiodarone's iodine-related organ toxicity, while its methane sulfonyl group decreases lipophilicity so shortening half-life and decreasing tissue accumulation. Electrophysiological studies show that dronedarone shares amiodarone's multichannel blocking effects, inhibiting transmembrane Na(+), K(+), Ca(2+), and slow L-type calcium channels, as well as its antiadrenergic effects. Unlike amiodarone, it has little effect at thyroid receptors. Possessing both rate- and rhythm-control properties, dronedarone has proved safe and effective in preventing recurrence of atrial fibrillation (AF) in patients with persistent AF in the Dronedarone Atrial Fibrillation Study After Electrical Cardioversion (DAFNE) trial, the first prospective randomized trial to evaluate its efficacy and safety. Dronedarone has since undergone further extensive evaluation in three pivotal phase III trials. In two sister studies, the European Trial in Atrial Fibrillation or Flutter Patients Receiving Dronedarone for the Maintenance of Sinus Rhythm (EURIDIS) and American-Australian-African Trial with Dronedarone in Atrial Fibrillation/Flutter Patients for the Maintenance of Sinus Rhythm (ADONIS), dronedarone 400 mg b.i.d. showed significant efficacy against placebo in prevention of AF recurrence. Additionally, in patients with permanent AF, dronedarone was highly effective at controlling ventricular rate on top of standard rate-controlling therapies in the Efficacy and Safety of Dronedarone for the Control of Ventricular Rate during Atrial Fibrillation (ERATO) study.

The Novel Antiarrhythmic Drug Dronedarone: Comparison with Amiodarone

Dronedarone is a noniodinated benzofuran derivative that has been developed to overcome the limiting iodine-associated adverse effects of the commonly used antiarrhythmic drug, amiodarone. It displays a wide cellular electrophysiological spectrum largely similar to amiodarone, inhibiting the potassium currents I(Kr), I(Ks), I(KI), I(KACh), and I(sus), as well as sodium currents and L-type calcium currents in isolated cardiomyocytes. In addition, dronedarone exhibits antiadrenergic properties. In vivo, dronedarone has been shown to be more effective than amiodarone in several arrhythmia models, particularly in preventing ischemia- and reperfusion-induced ventricular fibrillation and in reducing mortality. However, an increased incidence of torsades de pointes with dronedarone in dogs shows that possible proarrhythmic effects of dronedarone require further evaluation. The clinical trails DAFNE, EURIDIS, and ADONIS indicated safety, antiarrhythmic efficacy and low proarrhythmic potential of the drug in low-risk patients. In contrast, the increased incidence of death in the dronedarone group of the discontinued ANDROMEDA trial raises safety concerns for patients with congestive heart failure and moderate to severe left ventricular dysfunction. Dronedarone appears to be effective in preventing relapses of atrial fibrillation and atrial flutter. Torsades de pointes, the most severe adverse effect associated with amiodarone, has not yet been reported in humans with dronedarone. Unlike amiodarone, dronedarone had little effect on thyroid function and hormone levels in animal models and had no significant effects on human thyroid function in clinical trials. In conclusion, dronedarone could be a useful drug for prevention of atrial fibrillation and atrial flutter relapses in low-risk patients. However, further experimental studies and long-term clinical trials are required to provide additional evidence of efficacy and safety of dronedarone.

Acute effects of dronedarone on both components of the cardiac delayed rectifier K+ current, HERG and KvLQT1/minK potassium channels

Dronedarone is a noniodinated benzofuran derivative that has been synthesized to overcome the limiting iodine-associated adverse effects of the potent antiarrhythmic drug amiodarone. In this study, the acute electrophysiological effects of dronedarone on repolarizing potassium channels were investigated to determine the class III antiarrhythmic action of this compound. HERG and KvLQT1/minK potassium channels conduct the delayed rectifier potassium current IK in human heart, being a primary target for class III antiarrhythmic therapy. HERG and KvLQT1/minK were expressed heterologously in Xenopus laevis oocytes, and the respective potassium currents were recorded using the two-microelectrode voltage-clamp technique. Dronedarone blocked HERG channels with an IC50 value of 9.2 microM and a maximum tail current reduction of 85.2%. HERG channels were blocked in the closed, open, and inactivated states. The half-maximal activation voltage was shifted by -6.1 mV, and HERG current block by dronedarone was voltage-dependent, but not use-dependent. Dronedarone exhibited a weaker block of KvLQT1/minK currents (33.2% at 100 microM drug concentration), without causing significant changes in the corresponding current-voltage relationships. In conclusion, these data demonstrate that dronedarone is an antagonist of cloned HERG potassium channels, with additional inhibitory effects on KvLQT1/minK currents at higher drug concentrations, providing a molecular mechanism for the class III antiarrhythmic action of the drug.

Effects of amiodarone and dronedarone on voltage-dependent sodium current in human cardiomyocytes

Effect of Dronedarone on Cardiac Na Current.

INTRODUCTION

Amiodarone (AM) is a highly effective antiarrhythmic agent used in the management of both atrial and ventricular arrhythmias. Its noniodinated analogue dronedarone (SR) may have fewer side effects than AM. In this study, we compared the effects of AM and SR on the sodium current I(Na) in human atrial myocytes.

METHODS AND RESULTS

INa was studied with the whole-cell, patch clamp technique. Both AM and SR induced a dose-dependent inhibition of I(Na) recorded at -40 mV from a holding potential of -100 mV. AM inhibited I(Na) by 41%+/- 11% (n = 4) at 3 microM, and by 80%+/- 7% (n = 5) at 30 microM. SR produced more potent block, inhibiting INa significantly at only 0.3 microM (23%+/- 10%, n = 4) and completely (97%+/- 4%, n = 4) at 3 microM. Both AM and SR had only moderate effects on voltage-dependent properties of I(Na) (current-voltage relationship, availability for activation) and had no effect on the current decay kinetics.

CONCLUSION

Both AM and SR inhibit I(Na) significantly in single human atrial cells, showing that the two drugs have Class I antiarrhythmic properties. The acute effects of SR are more potent than those of AM. The study supports the idea that the iodinated form of the molecule has no part in the acute effect of AM on Na+ channels.

Effects of dronedarone and amiodarone on plasma thyroid hormones and on the basal and postischemic performance of the isolated rat heart

The present study investigated the effects of dronedarone and amiodarone on plasma thyroid hormones and the possible consequences on the response of the heart to ischemia. Amiodarone (30 mg/kg/day per os) or dronedarone (30 mg/kg/day per os) were administered for 2 weeks in normal and thyroxine-treated animals (25 microg/100 g body weight od sc, for 2 weeks), while animals without amiodarone and dronedarone served as controls. Isolated rat hearts were perfused in a Langendorff mode and subjected to 20 and 30 min of zero-flow global ischemia followed by 45 min of reperfusion. Functional changes were assessed by measuring left ventricular developed pressure (LVDP) under resting conditions and in response to ischemia-reperfusion, LVDP%, as well as the severity of ischemic contracture. Amiodarone resulted in increased T4, T4/T3 and rT3, whereas dronedarone did not alter the thyroid hormone profile in normal animals. In thyroxine-treated animals, amiodarone increased T4/T3 ratio but T4, T3 and rT3 levels were not altered. Basal functional parameters and ischemic contracture did not change by amiodarone and/or dronedarone neither in normal nor in thyroxine-treated hearts. In normal hearts, postischemic functional recovery, LVDP%, was not altered by amiodarone or dronedarone administration. LVDP% was statistically higher in thyroxine-treated hearts than in normal and this beneficial effect was not abolished by amiodarone or dronedarone treatment.

Hemodynamic and antiadrenergic effects of dronedarone and amiodarone in animals with a healed myocardial infarction

The hemodynamic and antiadrenergic effects of dronedarone, a noniodinated compound structurally related to amiodarone, were compared with those of amiodarone after prolonged oral administration, both at rest and during sympathetic stimulation in conscious dogs with a healed myocardial infarction. All dogs (n = 6) randomly received orally dronedarone (10 and 30 mg/kg), amiodarone (10 and 30 mg/kg), and placebo twice daily for 7 days, with a 3-week washout between consecutive treatments. Heart rate (HR), mean arterial pressure (MBP), positive rate of increase of left ventricular pressure (+LVdP/dt), echocardiographically assessed left ventricular ejection fraction (LVEF), and fractional shortening (FS), as well as chronotropic response to isoproterenol and exercise-induced sympathetic stimulation were evaluated under baseline and posttreatment conditions. Resting values of LVEF, FS, +LVdP/dt, and MBP remained unchanged whatever the drug and the dosing regimen, whereas resting HR was significantly and dose-dependently lowered after dronedarone and to a lesser extent after amiodarone. Both dronedarone and amiodarone significantly reduced the exercise-induced tachycardia and, at the highest dose, decreased the isoproterenol-induced tachycardia. Thus, dronedarone and amiodarone displayed a similar level of antiadrenergic effect and did not impair the resting left ventricular function. Consequently, dronedarone might be particularly suitable for the treatment and prevention of various clinical arrhythmias, without compromising the left ventricular function.