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Ebola Virus Disease is one of the most lethal transmissible infections characterized by a high fatality rate. Several research studies have aimed to identify effective antiviral agents. Amiodarone, a drug used for the treatment of arrhythmias, has been shown to inhibit filovirus infection in vitro by acting at the early step of the viral replication cycle. Here we demonstrate that amiodarone reduces virus binding to target cells and slows down the progression of the viral particles along the endocytic pathway. Overall our data support the notion that amiodarone interferes with Ebola virus infection by affecting cellular pathways/ targets involved in the viral entry process.

The ectopic overexpression of the voltage-dependent Eag1 (Kv10.1) K + channel is associated with the cancerous phenotype in about 70% of human cancers and tumor cell lines. Recent reports showed that, compared with the canonical Shaker-related Kv family, Kv10.1 presents unique structural and functional properties. Herein, we report the interaction of the class III anti-arrhythmic compound amiodarone with Kv10.1. Using whole-cell patch clamp, we found that amiodarone inhibits Kv10.1 channel conductance with nanomolar affinity. Additionally, and interestingly, we also report that amiodarone inhibits the characteristic Cole-Moore shift of Eag1 channels. Our observations are interpreted considering the structural-functional characteristics of these channels. We conclude that amiodarone possibly binds with high affinity to the voltage sensor module, altering the gating of Kv10.1.

Cardiac arrhythmia may occur in the course of epilepsy. Simultaneous therapy of the two diseases might be complicated by drug interactions since antiarrhythmic and antiepileptic agents share some molecular targets. The aim of this study was to evaluate the influence of amiodarone, an antiarrhythmic drug working as a multi-channel blocker, on the protective activity of four classical antiepileptic drugs in the maximal electroshock test in mice. Amiodarone at doses up to 75 mg/kg did not affect the electroconvulsive threshold in mice. Acute amiodarone at the dose of 75 mg/kg significantly potentiated the anticonvulsive effect of carbamazepine, but not that of valproate, phenytoin or phenobarbital in the maximal electroshock-induced seizures in mice. The antiarrhythmic agent and its combinations with antiepileptic drugs did not impair motor performance or long-term memory in mice, except for the combination of amiodarone and phenobarbital. Brain concentrations of antiepileptic drugs were not changed. Despite favourable impact of amiodarone on the anticonvulsive action of carbamazepine in the maximal electroshock, co-administration of the two drugs should be carefully monitored in clinical conditions. Further studies are necessary to evaluate effects of chronic treatment with amiodarone on seizure activity and the action of antiepileptic drugs., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Dronedarone is a CYP2D6 inhibitor; therefore, it is prudent to exercise caution when concurrently administering CYP2D6-metabolized β-blockers because of a lack of published data on potential drug interactions. The aim of this study was to investigate the effect of dronedarone on the pharmacokinetics of orally administered carvedilol in rats. Twenty male Sprague-Dawley rats were randomly divided into two groups and 10mg/kg carvedilol was administered to the rat with or without dronedarone pretreatment in a parallel design. Blood samples were collected before and after 0.25, 0.5, 0.75, 1, 2, 4, 6, 8, 12, and 24h of drug administration. The plasma concentration of carvedilol was determined using LC-MS/MS. The systemic exposure to carvedilol was significantly increased and elimination of carvedilol was significantly decreased in the dronedarone-pretreated rats than in the vehicle-pretreated rats. The one-compartment model with first-order absorption and elimination was sufficient to explain the pharmacokinetic characters after single oral administration of carvedilol to both vehicle-pretreated and dronedarone-pretreated rats. This study suggests that dronedarone inhibits CYP2D6-mediated carvedilol metabolism, and dose adjustment is needed in carvedilol and dronedarone combination therapy. Further studies are needed to clarify the effect of dronedarone on carvedilol and CYP2D6 substrates in clinical use., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Introduction: Approximately seven to eight million people worldwide have Chagas disease. In Brazil, benznidazole is the most commonly used active drug against Trypanosoma cruzi; however, its efficacy is limited, and side effects are frequent. Recent studies suggest that amiodarone may be beneficial in the treatment of this disease, by exerting anti-T. cruzi action. This study evaluated changes in T. cruzi cell count in in vitro cultures subjected to different doses of benznidazole, amiodarone, and their combination., Methods: T. cruzi (Y strain) cultures containing approximately 100,000 cells were treated with either 100mg, 50mg, 25mg, 12.5mg, or 10mg of benznidazole, amiodarone, or their combination. On the 4th day, cell count was compared to the baseline data., Results: On the 4th day, no parasites were observed in any of the treated cultures., Conclusions: Benznidazole and amiodarone were equally effective in eliminating T. cruzi in culture. The combination of the two drugs was also equally effective, but our data cannot demonstrate synergism, as similar results were obtained when the drugs were tested individually or in combination. It is suggested that this study be repeated with other T. cruzi strains to determine whether similar results can be obtained again.

Among comorbidity in chronic heart failure (CHF), dysthyroidism represents a relevant problem especially in the ageing CHF patients worldwide. Thyroid greatly affects many cardiovascular activities and its dysfunction may worsen a CHF condition. In particular, hypothyroidism has a relative high prevalence in patients with heart failure and it plays a key role in influencing CHF onset, progression and prognosis. Hyperthyroidism, is less frequent in this clinical context but it necessitates of immediate treatment because of its negative effects on cardiovascular balance. Also, it must be considered that dysthyroism may also be iatrogenic and the main responsible drug is Amiodarone.Based on the best available evidence and our cumulative clinical experience, this manuscript analyzes the prevalence, the pathophysiology and the prognostic impact of thyroid disorders in chronic heart failure.

Cardiac enzymes such as cytochrome P450 2J2 (CYP2J2) metabolize arachidonic acid (AA) to cardioprotective epoxyeicosatrienoic acids (EETs), which in turn are metabolized by soluble epoxide hydrolase (sEH) to dihydroxyeicosatrienoic acids (DHETs). As EETs and less potent DHETs exhibit cardioprotective and vasoprotective functions, optimum levels of cardiac EETs are paramount in cardiac homeostasis. Previously, we demonstrated that dronedarone, amiodarone and their main metabolites, namely N-desbutyldronedarone (NDBD) and N-desethylamiodarone (NDEA), potently inhibit human cardiac CYP2J2-mediated astemizole metabolism in vitro. In this study, we investigated the inhibition of recombinant human CYP450 enzymes (rhCYP2J2, rhCYP2C8, rhCYP2C9)-mediated AA metabolism and human recombinant sEH (rhsEH)-mediated EET metabolism by dronedarone, amiodarone, NDBD and NDEA. A static model describing sequential metabolism was further developed to predict the aggregate effect of dual-inhibition of rhCYP2J2 and rhsEH on the fold-of 14,15-EET level (C EET ' /C EET ). Dronedarone, amiodarone and NDBD inhibit rhCYP2J2-mediated metabolism of AA to 14,15-EET with K i values of 3.25, 5.48, 1.39µM respectively. Additionally, dronedarone, amiodarone, NDBD and NDEA inhibit rhsEH-mediated metabolism of 14,15-EET to 14,15-DHET with K i values of 5.10, 13.08, 2.04, 1.88µM respectively. Based on static sequential metabolism modelling, dronedarone (C EET ' /C EET =0.85), amiodarone (C EET ' /C EET =0.48) and NDBD (C EET ' /C EET =0.76) were predicted to decrease cardiac 14,15-EET level whereas NDEA (C EET ' /C EET >35.5) was predicted to elevate it. Based on our novel findings, we postulate the differential cardiac exacerbation potential of dronedarone and amiodarone is partly associated with their differential inhibition potencies of cardiac CYP2J2 and sEH., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Bladder cancer (BC) is a common malignancy of the urinary tract that has a higher frequency in men than in women. Cytostatic resistance and metastasis formation are significant risk factors in BC therapy; therefore, there is great interest in overcoming drug resistance and in initiating research for novel chemotherapeutic approaches. Here, we suggest that desethylamiodarone (DEA)-a metabolite of amiodarone-may have cytostatic potential. DEA activates the collapse of mitochondrial membrane potential (detected by JC-1 fluorescence), and induces cell death in T24 human transitional-cell bladder carcinoma cell line at physiologically achievable concentrations. DEA induces cell cycle arrest in the G0/G1 phase, which may contribute to the inhibition of cell proliferation, and shifts the Bax/Bcl-2 ratio to initiate apoptosis, induce AIF nuclear translocation, and activate PARP-1 cleavage and caspase-3 activation. The major cytoprotective kinases-ERK and Akt-are inhibited by DEA, which may contribute to its cell death-inducing effects. DEA also inhibits the expression of B-cell-specific Moloney murine leukemia virus integration site 1 (BMI1) and reduces colony formation of T24 bladder carcinoma cells, indicating its possible inhibitory effect on metastatic potential. These data show that DEA is a novel anti-cancer candidate of multiple cell death-inducing effects and metastatic potential. Our findings recommend further evaluation of its effects in clinical studies.

Purpose: Progress to the clinic may be delayed or prevented when vacuolated or "foamy" alveolar macrophages are observed during non-clinical inhalation toxicology assessment. The first step in developing methods to study this response in vitro is to characterize macrophage cell lines and their response to drug exposures., Methods: Human (U937) and rat (NR8383) cell lines and primary rat alveolar macrophages obtained by bronchoalveolar lavage were characterized using high content fluorescence imaging analysis quantification of cell viability, morphometry, and phospholipid and neutral lipid accumulation., Results: Cell health, morphology and lipid content were comparable (p < 0.05) for both cell lines and the primary macrophages in terms of vacuole number, size and lipid content. Responses to amiodarone, a known inducer of phospholipidosis, required analysis of shifts in cell population profiles (the proportion of cells with elevated vacuolation or lipid content) rather than average population data which was insensitive to the changes observed., Conclusions: A high content image analysis assay was developed and used to provide detailed morphological characterization of rat and human alveolar-like macrophages and their response to a phospholipidosis-inducing agent. This provides a basis for development of assays to predict or understand macrophage vacuolation following inhaled drug exposure.

Background and Aims: Dronedarone reduced the rate of stroke and transient ischemic attack in patients with paroxysmal atrial fibrillation (AF) in the ATHENA trial. This cannot be explained by its antiarrhythmic effect alone and may involve alternative mechanisms. This study aimed to investigate any direct effect of dronedarone on blood thrombogenicity, independent of its antiarrhythmic effects., Methods: Blood samples from patients with cardiovascular disease (n = 30) taking no anticoagulant or antiplatelet medication except aspirin were incubated with dronedarone's active metabolite (SR35021A) at 66 ng/ml (am-L) and 119 ng/ml (am-H), i.e., minimum and maximum mean C max reported after repeated 400 mg BID dosing. A third aliquot of blood was incubated with vehicle (Control). Antithrombotic effects of dronedarone were assessed using Coagulation Time (CT), Clot Formation Rate (CFR) and Maximum Clot Firmness (MCF) in ThromboElastoMetry and whole blood platelet aggregation in response to ADP, collagen and TRAP., Results: Compared to Control, mean CT was prolonged by am-L and am-H (164 ± 25 s vs. 180 ± 22 and 182 ± 32 s, respectively, p<0.01 for both). Small but statistically significant reductions were observed in CFR (am-L and am-H) and MCF (am-H). Platelet aggregation induced by ADP and TRAP was also reduced (p<0.05 for both) by am-H., Conclusions: Dronedarone exerts direct anticoagulant and antiplatelet effects on human blood in vitro that are independent of its antiarrhythmic actions. This suggests the reductions in ischemic events reported with dronedarone may not be due to amelioration of AF itself. Additional clinical studies are required to further improve understanding of the mechanisms involved., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Drug-induced ion channel trafficking disturbance can cause cardiac arrhythmias. The subcellular level at which drugs interfere in trafficking pathways is largely unknown. K IR 2.1 inward rectifier channels, largely responsible for the cardiac inward rectifier current (I K 1 ), are degraded in lysosomes. Amiodarone and dronedarone are class III antiarrhythmics. Chronic use of amiodarone, and to a lesser extent dronedarone, causes serious adverse effects to several organs and tissue types, including the heart. Both drugs have been described to interfere in the late-endosome/lysosome system. Here we defined the potential interference in K IR 2.1 backward trafficking by amiodarone and dronedarone. Both drugs inhibited I K 1 in isolated rabbit ventricular cardiomyocytes at supraclinical doses only. In HK-KWGF cells, both drugs dose- and time-dependently increased K IR 2.1 expression (2.0 ± 0.2-fold with amiodarone: 10 μM, 24 hrs; 2.3 ± 0.3-fold with dronedarone: 5 μM, 24 hrs) and late-endosomal/lysosomal K IR 2.1 accumulation. Increased K IR 2.1 expression level was also observed in the presence of Na v 1.5 co-expression. Augmented K IR 2.1 protein levels and intracellular accumulation were also observed in COS-7, END-2, MES-1 and EPI-7 cells. Both drugs had no effect on K v 11.1 ion channel protein expression levels. Finally, amiodarone (73.3 ± 10.3% P < 0.05 at -120 mV, 5 μM) enhanced I KIR 2.1 upon 24-hrs treatment, whereas dronedarone tended to increase I KIR 2.1 and it did not reach significance (43.8 ± 5.5%, P = 0.26 at -120 mV; 2 μM). We conclude that chronic amiodarone, and potentially also dronedarone, treatment can result in enhanced I K 1 by inhibiting K IR 2.1 degradation., (© 2017 The Authors. Journal of Cellular and Molecular Medicine published by John Wiley & Sons Ltd and Foundation for Cellular and Molecular Medicine.)

Background and Objectives: Several drugs used in CKD can prolong electrocardiographic conduction. We examined the use of electrocardiogram QT-prolonging medications in predialysis CKD and their association with QT duration., Design, Setting, Participants, & Measurements: In total, 3252 Chronic Renal Insufficiency Cohort participants with at least one study electrocardiogram between 2003 and 2011 were included. QT-prolonging medications used in 100 or more visits ( n =16,451 visits) along with diuretics and proton pump inhibitors, given their potential for electrolyte disturbances, were examined for QT interval prolongation., Results: Mean QT interval corrected for heart rate was at 414±21 (±SD) milliseconds and prolonged (≥450 milliseconds) in 4.6% of electrocardiograms. QT interval corrected for heart rate was inversely related to serum potassium and calcium. Medications classified as QT prolonging were taken at 76% of visits, with two or more of these taken at 33% of visits. Of 30 medications examined, eight were associated with statistically significant QT interval corrected for heart rate prolongation after adjustment for comorbidities, potassium, and calcium, including amiodarone (+10±2 milliseconds), metolazone (+7±2 milliseconds), fluoxetine (+4±1 milliseconds), citalopram (+4±1 milliseconds), hydroxyzine (+4±1 milliseconds), escitalopram (+3±2 milliseconds), venlafaxine (+3±1 milliseconds), and furosemide (+3±0 milliseconds). Potassium-depleting diuretics were associated with minimal decrements in potassium (between 0.1 and 0.3 mEq/L) and smaller changes in calcium. Diuretics associated with a change in QT interval corrected for heart rate before adjustment for potassium and calcium were metolazone (+8±3 milliseconds), furosemide (+4±1 milliseconds), and spironolactone (-3±3 milliseconds). Most of the QT prolongation associated with metolazone and furosemide, but not spironolactone, remained after adjustment for potassium and calcium. Proton pump inhibitors were not associated with QT prolongation., Conclusions: Use of medications associated with QT prolongation is common in CKD; the safety implications of these findings should be considered in these high-risk patients., Podcast: This article contains a podcast at https://www.asn-online.org/media/podcast/CJASN/2017&#95;08&#95;09&#95;CJASNPodcast&#95;17&#95;09&#95;b.mp3., (Copyright © 2017 by the American Society of Nephrology.)

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.

Background: Short QT syndrome (SQTS) is a newly identified clinical disorder associated with atrial and/or ventricular arrhythmias and increased risk of sudden cardiac death (SCD). The SQTS variant 3 is linked to D172N mutation to the KCNJ2 gene that causes a gain-of-function to the inward rectifier potassium channel current (I K1 ), which shortens the ventricular action potential duration (APD) and effective refractory period (ERP). Pro-arrhythmogenic effects of SQTS have been characterized, but less is known about the possible pharmacological treatment of SQTS. Therefore, in this study, we used computational modeling to assess the effects of amiodarone, class III anti-arrhythmic agent, on human ventricular electrophysiology in SQT3., Methods: The ten Tusscher et al. model for the human ventricular action potentials (APs) was modified to incorporate I K1 formulations based on experimental data of Kir2.1 channels (including WT, WT-D172N and D172N conditions). The modified cell model was then implemented to construct one-dimensional (1D) and 2D tissue models. The blocking effects of amiodarone on ionic currents were modeled using IC 50 and Hill coefficient values from literatures. Effects of amiodarone on APD, ERP and pseudo-ECG traces were computed. Effects of the drug on the temporal and spatial vulnerability of ventricular tissue to genesis and maintenance of re-entry were measured, as well as on the dynamic behavior of re-entry., Results: Amiodarone prolonged the ventricular cell APD and decreased the maximal voltage heterogeneity (δV) among three difference cells types across transmural ventricular wall, leading to a decreased transmural heterogeneity of APD along a 1D model of ventricular transmural strand. Amiodarone increased cellular ERP, prolonged QT interval and decreased the T-wave amplitude. It reduced tissue's temporal susceptibility to the initiation of re-entry and increased the minimum substrate size necessary to sustain re-entry in the 2D tissue., Conclusions: At the therapeutic-relevant concentration of amiodarone, the APD and ERP at the single cell level were increased significantly. The QT interval in pseudo-ECG was prolonged and the re-entry in tissue was prevented. This study provides further evidence that amiodarone may be a potential pharmacological agent for preventing arrhythmogenesis for SQT3 patients.

Accumulating evidences showed that thyroid hormone was participated in the functioning of the reproductive system, and an elevated level of thyroid hormones had a negative impact on reproductive system. However, the molecular basis for this observation still remains to be fully understood. Here, we show that l-Thyroxine significantly impaired human sperm motility. The molecular basis showed that thyroxine receptor stimulation triggers Phosphatidyl Inositol 3-kinase (PI3K)/Akt signaling activation leading to the E3 ligase MDM2 phosphorylation at serine 166, which directly interacted with p53 for degradation. p53 degradation caused a p53-dependent DNA damage checkpoint or repair dysfunction, which eventually results in DNA damage accumulation in sperm. Our results highlight that inhibition of PI3K/Akt pathway or p53 degradation is important in maintaining sperm motility in a thyroxine receptor (TR)-dependent manner., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Introduction: Multidrug resistance-associated protein 3 (MRP3), an efflux transporter on the hepatic basolateral membrane, may function as a compensatory mechanism to prevent the accumulation of anionic substrates (e.g., bile acids) in hepatocytes. Inhibition of MRP3 may disrupt bile acid homeostasis and is one hypothesized risk factor for the development of drug-induced liver injury (DILI). Therefore, identifying potential MRP3 inhibitors could help mitigate the occurrence of DILI., Methods: Bayesian models were developed using MRP3 transporter inhibition data for 86 structurally diverse drugs. The compounds were split into training and test sets of 57 and 29 compounds, respectively, and six models were generated based on distinct inhibition thresholds and molecular fingerprint methods. The six Bayesian models were validated against the test set and the model with the highest accuracy was utilized for a virtual screen of 1470 FDA-approved drugs from DrugBank. Compounds that were predicted to be inhibitors were selected for in vitro validation. The ability of these compounds to inhibit MRP3 transport at a concentration of 100μM was measured in membrane vesicles derived from stably transfected MRP3-over-expressing HEK-293 cells with [ 3 H]-estradiol-17β-d-glucuronide (E 2 17G; 10μM; 5min uptake) as the probe substrate., Results: A predictive Bayesian model was developed with a sensitivity of 73% and specificity of 71% against the test set used to evaluate the six models. The area under the Receiver Operating Characteristic (ROC) curve was 0.710 against the test set. The final selected model was based on compounds that inhibited substrate transport by at least 50% compared to the negative control, and functional-class fingerprints (FCFP) with a circular diameter of six atoms, in addition to one-dimensional physicochemical properties. The in vitro screening of predicted inhibitors and non-inhibitors resulted in similar model performance with a sensitivity of 64% and specificity of 70%. The strongest inhibitors of MRP3-mediated E 2 17G transport were fidaxomicin, suramin, and dronedarone. Kinetic assessment revealed that fidaxomicin was the most potent of these inhibitors (IC 50 =1.83±0.46μM). Suramin and dronedarone exhibited IC 50 values of 3.33±0.41 and 47.44±4.41μM, respectively., Conclusion: Bayesian models are a useful screening approach to identify potential inhibitors of transport proteins. Novel MRP3 inhibitors were identified by virtual screening using the selected Bayesian model, and MRP3 inhibition was confirmed by an in vitro transporter inhibition assay. Information generated using this modeling approach may be valuable in predicting the potential for DILI and/or MRP3-mediated drug-drug interactions., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Anti-atrial fibrillatory and proarrhythmic potentials of amiodarone were simultaneously analyzed by using the halothane-anesthetized beagle dogs (n = 4) in order to begin to prepare standard protocol for clarifying both efficacy and adverse effects of anti-atrial fibrillatory drugs. Intravenous administration of 0.3 mg/kg of amiodarone hydrochloride decreased the heart rate and mean blood pressure. Additional administration of 3 mg/kg of amiodarone hydrochloride prolonged the QT interval besides the effects observed by the low dose, whereas it showed 1.6 times larger prolongation in the effective refractory period of the atrium than that of the ventricle, which may explain its clinical efficacy against atrial arrhythmias. However, no significant change was detected by either dose in the early repolarization assessed by corrected J-T peak or the late repolarization done by T peak -T end in the electrocardiogram, although the former tended to be shortened and the reverse was true for the latter. Lack of prolongation in the early repolarization will make it feasible to better understand why amiodarone lacks proarrhythmic potential in spite of the QT-interval prolongation. Thus, these results of amiodarone obtained by current protocol may become a guidance on assessing efficacy and adverse effects of new anti-atrial fibrillatory drugs in vivo.

Background: Ventricular tachycardia (VT) and ventricular fibrillation are the causes of approximately 300,000 deaths per year in the United States. VT is classified based on hemodynamic status and appearance. Stable, monomorphic VT treatment is controversial., Objective: Our aim was to provide emergency physicians with an evidence-based review of the medical management of stable, monomorphic VT., Discussion: Stable, monomorphic VT is part of a larger class of ventricular dysrhythmias defined by a rate of at least 120 beats/min with QRS > 120 ms without regularly occurring P:QRS association. Little controversy exists for the treatment of hemodynamically unstable VT. The medical management of hemodynamically stable monomorphic VT is surrounded by controversy. Direct current cardioversion is most efficacious. Guidelines for the treatment of stable VT from the American Heart Association provide a IIa recommendation for procainamide, compared with a IIb recommendation for both amiodarone and sotalol. Studies evaluating procainamide, lidocaine, amiodarone, and sotalol suffer from poor design, difference in inclusion and exclusion criteria, small sample size, and outcome determination. Procainamide demonstrates the greatest efficacy. If procainamide is selected, a maximum dose of 10 mg/kg at 50-100 mg/min intravenous (IV) over 10-20 min should be provided with monitoring of blood pressure and electrocardiogram. Monomorphic VT with acute myocardial ischemia requires further study., Conclusions: Optimal management of stable, monomorphic VT includes direct current cardioversion. If medical management is chosen, procainamide is most efficacious, though current literature suffers from poor design., (Published by Elsevier Inc.)

Background: Oral tyrosine kinase inhibitors (TKIs) are becoming increasingly common in oncology practice due to ease of administration and patient preference. This class of medications is relatively unknown to emergency physicians., Case Report: Here we present a case of electrical storm (ES) thought to be associated with ibrutinib, a TKI. The ES was unabated despite antidysrhythmic therapy and electrical cardioversion, and was treated with supportive care, which eventually included the use of extracorporeal membrane oxygenation. This patient had no risk factors or apparent causes of recurrent ventricular tachycardia. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: ES has not previously been described with ibrutinib, but may be associated with off-target effects of the drug., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Severe bradycardia/bradyarrhythmia following coadministration of the HCV-NS5B prodrug sofosbuvir with amiodarone was recently reported. Our previous preclinical in vivo experiments demonstrated that only certain HCV-NS5B prodrugs elicit bradycardia when combined with amiodarone. In this study, we evaluate the impact of HCV-NS5B prodrug phosphoramidate diastereochemistry (D-/L-alanine, R-/S-phosphoryl) in vitro and in vivo. Co-applied with amiodarone, L-ala,S P prodrugs increased beating rate and decreased beat amplitude in human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs), but D-ala,R P produgs, including MK-3682, did not. Stereochemical selectivity on emerging bradycardia was confirmed in vivo. Diastereomer pairs entered cells equally well, and there was no difference in intracellular accumulation of L-ala,S P metabolites ± amiodarone, but no D-ala,R P metabolites were detected. Cathepsin A (CatA) inhibitors attenuated L-ala,S P prodrug metabolite formation, yet exacerbated L-ala,S P  + amiodarone effects, implicating the prodrugs in these effects. Experiments indicate that pharmacological effects and metabolic conversion to UTP analog are L-ala,S P prodrug-dependent in cardiomyocytes.

This article is one of ten reviews selected from the Annual Update in Intensive Care and Emergency medicine 2017. Other selected articles can be found online at http://ccforum.com/series/annualupdate2017 . Further information about the Annual Update in Intensive Care and Emergency Medicine is available from http://www.springer.com/series/8901 .

Introduction: We examined the effects of the selective late INa inhibitor eleclazine on the 50% probability of successful defibrillation (DFT50) before and after administration of amiodarone to determine its suitability for use in patients with implantable cardioverter defibrillators (ICDs)., Methods and Results: In 20 anesthetized pigs, transvenous active-fixation cardiac defibrillation leads were fluoroscopically positioned into right ventricular apex through jugular vein. ICDs were implanted subcutaneously. Dominant frequency of ventricular fibrillation was analyzed by fast Fourier transform. The measurements were made before drug administration (control), and at 40 minutes after vehicle, eleclazine (2 mg/kg, i.v., bolus over 15 minutes), or subsequent/single amiodarone administration (10 mg/kg, i.v., bolus over 10 minutes). Eleclazine did not alter DFT50, dominant frequency, heart rate, or mean arterial pressure (MAP). Subsequent amiodarone increased DFT50 (P = 0.006), decreased dominant frequency (P = 0.022), and reduced heart rate (P = 0.031) with no change in MAP. Amiodarone alone increased DFT50 (P = 0.005; NS compared to following eleclazine) and decreased dominant frequency (P = 0.003; NS compared to following eleclazine)., Conclusion: Selective late INa inhibition with eleclazine does not alter DFT50 or dominant frequency of ventricular fibrillation when administered alone or in combination with amiodarone. Accordingly, eleclazine would not be anticipated to affect the margin of defibrillation safety in patients with ICDs.

Decreased brain glutamate level has emerged as a new therapeutic approach for epilepsy. This study investigated the effect and mechanism of amiodarone, an anti-arrhythmic drug with antiepileptic activity, on glutamate release in the rat hippocampus. In a synaptosomal preparation, amiodarone reduced 4-aminopyridine-evoked Ca 2+ -dependent glutamate release and cytosolic Ca 2+ concentration elevation. Amiodarone did not affect the 4-aminopyridine-evoked depolarization of the synaptosomal membrane potential or the Na + channel activator veratridine-evoked glutamate release, indicating that the amiodarone-mediated inhibition of glutamate release is not caused by a decrease in synaptosomal excitability. The inhibitory effect of amiodarone on 4-aminopyridine-evoked glutamate release was markedly decreased in synaptosomes pretreated with the Ca v 2.2 (N-type) and Ca v 2.1 (P/Q-type) channel blocker ω-conotoxin MVIIC, the calmodulin antagonists W7 and calmidazolium, or the protein kinase A inhibitors H89 and KT5720. However, the intracellular Ca 2+ -release inhibitors dantrolene and CGP37157 had no effect on the amiodarone-mediated inhibition of glutamate release. Furthermore, amiodarone reduced the frequency of miniature excitatory postsynaptic currents without affecting their amplitude in hippocampal slices. Our data suggest that amiodarone reduces Ca 2+ influx through N- and P/Q-type Ca 2+ channels, subsequently reducing the Ca 2+ -calmodulin/protein kinase A cascade to inhibit the evoked glutamate release from rat hippocampal nerve terminals., (Copyright © 2017 The Authors. Production and hosting by Elsevier B.V. All rights reserved.)

Background: A post hoc analysis of the PALLAS trial suggested possible interactions of dronedarone and digitalis glycosides. The aim of the present study was to compare the effects dronedarone or amiodarone in combination with digitalis glycosides., Methods and Results: Eleven female rabbits underwent chronic oral treatment with amiodarone (50mg/kg/d for 6weeks). Ten rabbits were treated with dronedarone (50mg/kg/d for 6weeks). Ten rabbits were used as controls. Hearts were isolated and Langendorff-perfused. Monophasic action potentials and ECG showed a moderate prolongation of QT interval and action potential duration (APD). Both drugs also increased effective refractory period. Additional application of ouabain (0.2μM) resulted in a significant decrease of QT interval, APD, and ERP in all groups. Ventricular arrhythmias were induced by programmed ventricular stimulation and aggressive burst stimulation. Reproducible occurrence was defined as occurrence of at least 3 episodes. Under baseline conditions in control hearts, ventricular fibrillation (VF) was inducible in 1 of 10 hearts (7 episodes). After the application of 0.2μM ouabain, 4 of 10 control hearts were inducible (24 episodes). One of 10 dronedarone-pretreated hearts (3 episodes) and 2 of 11 amiodarone-pretreated hearts (6 episodes) showed VF before ouabain infusion. After the application of 0.2μM ouabain, 7 of 10 dronedarone-pretreated hearts were inducible (73 episodes). By contrast, only 4 of 11 amiodarone-pretreated hearts (13 episodes) showed VF., Conclusion: In the present study, additional treatment with ouabain resulted in an increased ventricular vulnerability in al study groups. Of note, chronically dronedarone-pretreated hearts were significantly more vulnerable than amiodarone-pretreated hearts., (Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.)

Truncated oxidized glycerophospholipids (ox-PLs) are bioactive lipids resulting from oxidative stress. The catabolic pathways for truncated ox-PLs are not fully understood. Lysosomal phospholipase A2 (LPLA2) with phospholipase A and transacylase activities is a key enzyme in phospholipid homeostasis. The present study assessed whether LPLA2 could hydrolyze truncated ox-PLs. Incubation of LPLA2 with liposomes consisting of 1,2-O-octadecenyl-sn-glycero-3-phosphocholine (DODPC)/1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) or truncated oxidized phosphatidylcholine (ox-PC)/N-acetylsphingosine (NAS) under acidic conditions resulted in the preferential deacylation at the sn-1 position of the truncated ox-PCs. Additionally, the release of free fatty acid from the truncated ox-PCs preferentially occurred compared with the NAS-acylation. Incubation of LPLA2 with the liposomes consisting of DODPC/DOPC/truncated ox-PC/NAS resulted in the same preferential fatty acid release from the truncated ox-PC. The cationic amphiphilic drug, amiodarone, did not inhibit such fatty acid release, indicating that truncated ox-PCs partition from the lipid membrane into the aqueous phase and react with free LPLA2. Consistent with this mechanism, the hydrolysis of some truncated ox-PCs, but not DOPC, by LPLA2 was detected at neutral pH. Additionally, LPLA2-overexpressed Chinese hamster ovary cells efficiently catabolized truncated ox-PC and were protected from growth inhibition. These findings support the existence of a novel catabolic pathway for truncated ox-PLs via LPLA2., (Copyright © 2017 by the American Society for Biochemistry and Molecular Biology, Inc.)

Correlative NanoSIMS and EM imaging of amiodarone-treated macrophages shows the internalisation of the drug at a sub-cellular level and reveals its accumulation within the lysosomes, providing direct evidence for amiodarone-induced phospholipidosis. Chemical fixation using tannic acid effectively seals cellular membranes aiding intracellular retention of diffusible drugs.

Dantrolene was introduced for treatment of malignant hyperthermia. It also has antiarrhythmic properties and may thus be an alternative to amiodarone for the treatment of ventricular fibrillation (VF). Aim of this study was to compare the return of spontaneous circulation (ROSC) with dantrolene and amiodarone in a pig model of cardiac arrest. VF was induced in anesthetized pigs. After 8 min of untreated VF, chest compressions and ventilation were started and one of the drugs (amiodarone 5 mg kg -1 , dantrolene 2.5 mg kg -1 or saline) was applied. After 4 min of initial CPR, defibrillation was attempted. ROSC rates, hemodynamics and cerebral perfusion measurements were measured. Initial ROSC rates were 7 of 14 animals in the dantrolene group vs. 5 of 14 for amiodarone, and 3 of 10 for saline). ROSC persisted for the 120 min follow-up in 6 animals in the dantrolene group, 4 after amiodarone and 2 in the saline group (n.s.). Hemodynamics were comparable in both dantrolene group amiodarone group after obtaining ROSC. Dantrolene and amiodarone had similar outcomes in our model of prolonged cardiac arrest, However, hemodynamic stability was not significantly improved using dantrolene. Dantrolene might be an alternative drug for resuscitation and should be further investigated., Competing Interests: TW is involved with B. Braun (advisory board) HW is involved with Teleflex, Vygon an B. Braun (speaker fees), TS is involved with Teleflex, Vygon and B.Braun (advisory board). None of the other authors declared any competing interests.

Background: Amiodarone is prescribed for certain cardiac arrhythmias in current medical practice. The drug targets and inhibits voltage dependent sodium (Na+ v), calcium (Ca+2 v), potassium (K+ v) channels, enzymes like cytochrome P450 and oxidosqualene cyclase. Past studies have shown that amiodarone exerts antiparasitic effects against Trypanosoma cruzi and Acanthamoeba castellanii., Objectives: The presence of aforementioned targets and the type of cell death induced by amiodarone in pathogenic eukaryotes like Acanthamoeba castellanii remains to be established. We inferred the presence of homologous targets of amiodarone in A. castellanii compared with humans., Methods: This study used bioinformatics exploration for amino acid sequence homology, ligand binding attribute predictions, 3D structural model development, and experimental assays that highlight similarity between certain target proteins in Acanthamoeba as compared to humans., Results: The sequence identity scores for amino acids and 3D models show that A. castellanii expresses similar types of targets of amiodarone like Na+ v - K+1 v channels, cytochrome P450 3A4, and lanosterol synthase (oxidosqualene cyclase). We show that even though human like L-type and two pore Ca+2 channels are present in A. castellanii, there was no evidence of the expression of T-type voltage dependent Ca+2 channels. Growth assays showed amoebicidal and amoebistatic effects at doses of 40-80μg/ml., Conclusion: The existing bioinformatics tools, ligand binding attribute prediction, and model building offer a specific method to establish homology of proteins, discover drug targets, and facilitate the investigation of the evolution of several types of cardinal ion channels from unicellular eukaryotes to multicellular species as humans., (Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.org.)

Background: Sofosbuvir is a direct-acting antiviral drug used to treat chronic hepatitis C infection. In 2015, Gilead Sciences, the manufacturer of sofosbuvir, warned that bradycardia could occur when sofosbuvir is administered in combination with amiodarone. Interestingly, among the reported cases of patients with sofosbuvir and amiodarone related bradycardia, some of them were also treated with propranolol., Objective: We herein report a case of ventricular extrasystoles within three hours after the coadministration of sofosbuvir-containing regimen with propranolol. This patient had never been treated with amiodarone. After the sofosbuvir-containing regimen was stopped, ventricular extrasystoles disappeared within 24 hours. This observation suggests that the association of sofosbuvir with propranolol may have a role in the emergence of cardiac arrhythmia., Conclusion: Patients treated with amiodarone and/or propranolol should be continuously monitored within the early hours following the initiation of sofosbuvir., (Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.org.)

We have previously reported that amiodarone interacts with a novel allosteric site on muscarinic receptors. Amiodarone's most striking effect is to enhance the maximal response elicited by muscarinic agonists at the M1, M3, and M5 receptors. Furthermore, the quaternary analog N-ethylamiodarone (NEA) is inhibitory at these receptors and appears to compete with amiodarone at that allosteric site. In the present studies, we show that dronedarone also modulates Gq-mediated responses at M1 and M3, although in a more discriminating manner. For example, dronedarone markedly enhances pilocarpine-stimulated release of arachidonic acid from CHO cells, via the M3 receptor subtype, but does not affect the acetylcholine-stimulated response. Such probe-dependent effects are diagnostic of an allosteric interaction. In comparison to these effects at M3, dronedarone is strongly inhibitory toward both pilocarpine and acetylcholine at the M1 subtype. The effects of dronedarone are consistent with an interaction at the amiodarone site: dronedarone inhibits the enhancement of acetylcholine's response produced by amiodarone at the M3 subtype; also, NEA reverses the enhancement of pilocarpine's response at M3 produced by either dronedarone or amiodarone. In studies with the M1-selective allosteric agonist 4-[3-(4-butylpiperidin-1-yl)-propyl]-7-fluoro-4H-benzo[1,4]oxazin-3-one (AC-260584), amiodarone enhanced the maximal response observed, whereas dronedarone was inhibitory. On the other hand, benzyl quinolone carboxylic acid, the well-known allosteric ligand that dramatically enhances the potency of acetylcholine at the M1 subtype, had no effect on the response profile of AC-260584. In summary, dronedarone acts at M1 and M3 muscarinic receptors in a manner that complements amiodarone and provides an additional tool with which to investigate this novel allosteric site., (© 2016 S. Karger AG, Basel.)

Aim: We assessed whether antiarrhythmic drug-induced QT interval prolongation affects left ventricular function., Methods: Study population included 54 patients with symptomatic recent onset atrial fibrillation spontaneously cardioverted to sinus rhythm. Electrocardiographic and echocardiographic studies were done before initiating and after achieving drug's steady state., Results: Significantly prolonged corrected QT interval (QTc) was noticed following only sotalol and amiodarone. The corrected precontraction time increased after sotalol (p = 0.005) and amiodarone (p = 0.017), not propafenone (p = 0.139). Analysis results between ΔEF and ΔQTc, ΔEF and ΔQTc(p), ΔE/e' and ΔQTc, ΔE/e' and ΔQTc(p) for amiodarone group were (p = 0.66, p = 0.20, p = 0.66, p = 0.33), for sotalol (p = 0.36, p = 0.51, p = 0.44, p = 0.33) and for propafenone (p = 0.38, p = 0.12, p = 0.89, p = 0.61), respectively., Conclusion: QT interval prolongation following antiarrhythmic therapy does not affect significantly left ventricular function.

Dose is an important parameter in terms of both efficacy and adverse effects in pharmacological treatment of atrial fibrillation (AF). Both of the class III antiarrhythmics dofetilide and amiodarone have documented anti-AF effects. While dofetilide has dose-related ventricular side effects, amiodarone primarily has adverse non-cardiac effects. Pharmacological inhibition of small conductance Ca 2+ -activated K + (SK) channels has recently been reported to be antiarrhythmic in a number of animal AF models. In a Langendorff model of acutely induced AF on guinea pig hearts, it was investigated whether a combination of the SK channel blocker N-(pyridin-2-yl)-4-(pyridin-2-yl)thiazol-2-amine (ICA) together with either dofetilide or amiodarone provided a synergistic effect. The duration of AF was reduced with otherwise subefficacious concentrations of either dofetilide or amiodarone when combined with ICA, also at a subefficacious concentration. At a concentration level effective as monotherapy, dofetilide produced a marked increase in the QT interval. This QT prolonging effect was absent when combined with ICA at non-efficacious monotherapy concentrations. The results thereby reveal that combination of subefficacious concentrations of an SK channel blocker and either dofetilide or amiodarone can maintain anti-AF properties, while the risk of ventricular arrhythmias is reduced.

In 2015, European and U.S. health agencies issued warning letters in response to 9 reported clinical cases of severe bradycardia/bradyarrhythmia in hepatitis C virus (HCV)-infected patients treated with sofosbuvir (SOF) in combination with other direct acting antivirals (DAAs) and the antiarrhythmic drug, amiodarone (AMIO). We utilized preclinical in vivo models to better understand this cardiac effect, the potential pharmacological mechanism(s), and to identify a clinically translatable model to assess the drug-drug interaction (DDI) cardiac risk of current and future HCV inhibitors. An anesthetized guinea pig model was used to elicit a SOF+AMIO-dependent bradycardia. Detailed cardiac electrophysiological studies in this species revealed SOF+AMIO-dependent selective nodal dysfunction, with initial, larger effects on the sinoatrial node. Further studies in conscious, rhesus monkeys revealed an emergent bradycardia and bradyarrhythmia in 3 of 4 monkeys administered SOF+AMIO, effects not observed with either agent alone. Morever, bradycardia and bradyarrhythmia were not observed in rhesus monkeys when intravenous infusion of MK-3682 was completed after AMIO pretreatment., Conclusions: These are the first preclinical in vivo experiments reported to replicate the severe clinical SOF+AMIO cardiac DDI and provide potential in vivo mechanism of action. As such, these data provide a preclinical risk assessment paradigm, including a clinically relevant nonhuman primate model, with which to better understand cardiovascular DDI risk for this therapeutic class. Furthermore, these studies suggest that not all HCV DAAs and, in particular, not all HCV nonstructural protein 5B inhibitors may exhibit this cardiac DDI with amiodarone. Given the selective in vivo cardiac electrophysiological effect, these data enable targeted cellular/molecular mechanistic studies to more precisely identify cell types, receptors, and/or ion channels responsible for the clinical DDI. (Hepatology 2016;64:1430-1441)., (© 2016 by the American Association for the Study of Liver Diseases.)

Several clinical cases of severe bradyarrhythmias have been reported upon co-administration of the Hepatitis-C NS5B Nucleotide Polymerase Inhibitor (HCV-NI) direct-acting antiviral agent, sofosbuvir (SOF), and the Class-III anti-arrhythmic amiodarone (AMIO). We model the cardiac drug-drug interaction (DDI) between AMIO and SOF, and between AMIO and a closely-related SOF analog, MNI-1 (Merck Nucleotide Inhibitor #1), in functional assays of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs), to provide mechanistic insights into recently reported clinical cases. AMIO co-applied with SOF or MNI-1 increased beating rate or field potential (FP) rate and decreased impedance (IMP) and Ca(2+) transient amplitudes in hiPSC-CM syncytia. This action resembled that of Ca(2+) channel blockers (CCBs) in the model, but CCBs did not substitute for AMIO in the DDI. AMIO analog dronedarone (DRON) did not substitute for, but competed with AMIO in the DDI. Ryanodine and thapsigargin, decreasing intracellular Ca(2+) stores, and SEA-0400, a Na(+)/Ca(2+) exchanger-1 (NCX1) inhibitor, partially antagonized or suppressed DDI effects. Other agents affecting FP rate only exerted additive or subtractive effects, commensurate with their individual effects. We also describe an interaction between AMIO and MNI-1 on Cav1.2 ion channels in an over-expressing HEK-293 cell line. MNI-1 enhanced Cav1.2 channel inhibition by AMIO, but did not affect inhibition of Cav1.2 by DRON, verapamil, nifedipine, or diltiazem. Our data in hiPSC-CMs indicate that HCV-NI agents such as SOF and MNI-1 interact with key intracellular Ca(2+)-handling mechanisms. Additional study in a Cav1.2 HEK-293 cell-line suggests that HCV-NIs potentiate the inhibitory action of AMIO on L-type Ca(2+) channels., (Copyright © 2016 Elsevier Inc. All rights reserved.)

There has been an increased focus on heart rate as a target in the management of cardiovascular disease and more specifically in heart failure with preserved ejection fraction in recent years with several studies showing the benefit of a lower resting heart rate on outcomes. This review paper examines the pathophysiology behind the benefits of lowering heart rate in heart failure and also the evidence for and against the pharmacological agents available to achieve this.

Cation trapping in acidic cell compartments determines an antiproliferative effect that has a potential interest in oncology, as shown by clinical data and trials involving chloroquine and hydroxychloroquine. To further characterize the mechanism of this effect, we studied a series of 6 substituted triethylamine (s-Et3N) drugs that encompasses a wide range of liposolubility (amiodarone, quinacrine, chloroquine, hydroxychloroquine, lidocaine, and procainamide). Three tumor cell lines and primary human endothelial cells were exploited in proliferation assays (48h, cell counts). Accumulation of the autophagic effector LC3 II and the apoptotic marker cleaved PARP1 (immunoblots), cytotoxicity, cell cycle analysis and endocytic function were further tested in the p53-null histiocytic lymphoma U937 line. A profound and desynchronized antiproliferative effect was observed in response to all s-Et3Ns with essentially no cell type specificity. Predictors of s-Et3N potency were liposolubility and the acute accumulation of the autophagic effector LC3 II (6h-treatments). For each s-Et3N, there was an antiproliferative concentration range where cytotoxicity and apoptosis were not triggered in U937 cells (24-48h-treatments). Quinacrine was the most potent cytostatic drug (1-5μM). Co-treatment of cells with inhibitors of cholesterol, β-cyclodextrin or lovastatin, partially reversed the antiproliferative effect of each s-Et3N. The cytopathology induced by cationic drug accumulation includes a cytostatic effect. Its intensity is cell type- and p53-independent, but predicted by the inhibition of autophagic flux and by the liposolubility of individual drugs and alleviated by cholesterol ablation. The superiority of quinacrine, biomarker value of LC3 II and antagonism by a statin may be clinically relevant., (Copyright © 2016 Elsevier Inc. All rights reserved.)

The antiarrhythmic drug amiodarone delays cardiac repolarisation through inhibition of hERG-encoded potassium channels responsible for the rapid delayed rectifier potassium current (IKr). This study aimed to elucidate molecular determinants of amiodarone binding to the hERG channel. Whole-cell patch-clamp recordings were made at 37°C of ionic current (IhERG) carried by wild-type (WT) or mutant hERG channels expressed in HEK293 cells. Alanine mutagenesis and ligand docking were used to investigate the roles of pore cavity amino-acid residues in amiodarone binding. Amiodarone inhibited WT outward IhERG tails with a half-maximal inhibitory concentration (IC50) of ∼45nM, whilst inward IhERG tails in a high K(+) external solution ([K(+)]e) of 94mM were blocked with an IC50 of 117.8nM. Amiodarone's inhibitory action was contingent upon channel gating. Alanine-mutagenesis identified multiple residues directly or indirectly involved in amiodarone binding. The IC50 for the S6 aromatic Y652A mutation was increased to ∼20-fold that of WT IhERG, similar to the pore helical mutant S624A (∼22-fold WT control). The IC50 for F656A mutant IhERG was ∼17-fold its corresponding WT control. Computational docking using a MthK-based hERG model differentiated residues likely to interact directly with drug and those whose Ala mutation may affect drug block allosterically. The requirements for amiodarone block of aromatic residues F656 and Y652 within the hERG pore cavity are smaller than for other high affinity IhERG inhibitors, with relative importance to amiodarone binding of the residues investigated being S624A∼Y652A>F656A>V659A>G648A>T623A., (Copyright © 2016 The Author(s). Published by Elsevier Inc. All rights reserved.)

We examined the inhibitory effect of amiodarone, a class III anti-arrhythmic agent, on voltage-dependent K(+) (Kv) currents in freshly isolated rabbit coronary arterial smooth muscle cells, using a whole-cell patch clamp technique. Amiodarone inhibited Kv currents in a concentration-dependent manner, with a half-maximal inhibitory concentration (IC50) value of 3.9 ± 1.44 μM and a Hill coefficient of 0.45 ± 0.14. Amiodarone did not have a significant effect on the steady-state activation of Kv channels, but shifted the inactivation current toward a more negative potential. Application of consecutive pulses progressively augmented the amiodarone-induced Kv channel inhibition. Another class III anti-arrhythmic agent, dofetilide, did not inhibit the Kv current or change the inhibitory effect of amiodarone on Kv channels. Therefore, these results strongly suggest that amiodarone inhibits Kv currents in a concentration- and state-dependent manner.

Dronedarone is a multichannel blocking antiarrhythmic drug that has been used for management of atrial fibrillation in humans, but the data in veterinary medicine are inadequate. The objective of this study was to determine the short-term effects of oral dronedarone on cardiac inotropy and lusitropy, blood pressure and electrocardiogram (ECG) in healthy dogs. A total of 6 beagle dogs were instrumented with telemetry units and sono-micrometry crystals to obtain left ventricular pressure-volume relationship, mean blood pressure (MBP) and ECG. Dogs were given orally dronedarone (20 mg/kg, twice per day) for 7 days. All parameters were obtained hourly at 4-8 hr after the first dose and at 12-, 96- (day 4) and 168-hr (day 7) after dosing. The results showed that dronedarone had no effect on inotropy and lusitropy, while it significantly lengthened PQ interval (P<0.001) and lowered MBP (P<0.05). Dronedarone also tended to reduce cardiac output (P=0.237) and heart rate (P=0.057). These results suggested that short-term effects of oral dronedarone administration at a dose of 20 mg/kg, twice per day, produced negative dromotropy with minimal effect on cardiac function in conscious dogs.

Background: In order to begin to precisely clarify the impact of renal denervation on the blood pressure, atrial fibrillation and ventricular tachyarrhythmias, in addition to proarrhythmic potential, its cardiovascular effects were assessed by using the chronic complete atrioventricular block dogs., Methods and results: Cardiohemodynamic and electrophysiological effects, together with neurohumoral factors and/or electrolytes, were assessed before and 4 weeks after either renal denervation (n=5) or amiodarone treatment (n=6). Amiodarone hydrochloride was given orally to the animals every day in a dose of 200 mg/day for the first 7 days followed by 100 mg/day for the following 21 days. The renal denervation decreased the systolic pressure, idioventricular rate, prolonged ventricular effective refractory period, and slightly suppressed the adrenergic tone and the renin-angiotensin-aldosterone system, but hardly affected the atrial effective refractory period and terminal repolarization period. Amiodarone prolonged the atrial effective refractory period, whereas no significant change was detected in the other variables., Conclusions: Surgically performed renal denervation may possess the anti-ventricular tachyarrhythmic rather than anti-atrial fibrillatory potentials, and it also modestly decreased the blood pressure. Thus, currently obtained information may be used as guidance for better understanding the utility and limitation of renal denervation against various types of cardiovascular diseases. (Circ J 2016; 80: 1556-1563).

Dronedarone is the newest antiarrhythmic drug approved for the maintenance of sinus rhythm in patients with nonpermanent atrial fibrillation (AF). It is a multi-channel blocker with diverse electrophysiologic properties. Dronedarone decreases the incidence of AF recurrence and the ventricular rate during recurrence. Dronedarone decreases rates of cardiovascular hospitalizations in patients with paroxysmal and persistent AF. Dronedarone increases mortality in patients with permanent AF and those with moderate-severe heart failure, and should thus be avoided in these populations. Dronedarone is less effective than amiodarone but also has less toxicity. Direct comparison with other antiarrhythmic drugs is not available., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Dronedarone, a multiple ion channel blocker is prescribed for the treatment of paroxysmal and persistent atrial fibrillation. While dronedarone does not precipitate toxicities like its predecessor amiodarone, its clinical use has been associated with idiosyncratic hepatic and cardiac adverse effects and drug-drug interactions (DDIs). As dronedarone is a potent mechanism-based inactivator of CYP3A4 and CYP3A5, a question arose if it exerts a similar inhibitory effect on CYP2J2, a prominent cardiac CYP450 enzyme. In this study, we demonstrated that CYP2J2 is reversibly inhibited by dronedarone (Ki=0.034 μM), amiodarone (Ki=4.8μM) and their respective pharmacologically active metabolites namely N-desbutyldronedarone (NDBD) (Ki=0.55 μM) and N-desethylamiodarone (NDEA) (Ki=7.4 μM). Moreover, time-, concentration- and NADPH-dependent irreversible inactivation of CYP2J2 was investigated where inactivation kinetic parameters (KI, kinact) and partition ratio (r) of dronedarone (0.05 μM, 0.034 min(-1), 3.3), amiodarone (0.21 μM, 0.015 min(-1), 20.7) and NDBD (0.48 μM, 0.024 min(-1), 21.7) were observed except for NDEA. The absence of the characteristic Soret peak, lack of recovery of CYP2J2 activity upon dialysis, and biotransformation of dronedarone and NDBD to quinone-oxime reactive metabolites further confirmed the irreversible inactivation of CYP2J2 by dronedarone and NDBD is via the covalent adduction of CYP2J2. Our novel findings illuminate the possible mechanisms of DDIs and cardiac adverse effects due to both reversible inhibition and irreversible inactivation of CYP2J2 by dronedarone, amiodarone and their active metabolites., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Introduction: Pharmacological rhythm control of atrial fibrillation (AF) in patients with structural heart disease is limited. Ranolazine in combination with low dose dronedarone remarkably reduced AF-burden in the phase II HARMONY trial. We thus aimed to investigate the possible mechanisms underlying these results., Methods and Results: Patch clamp experiments revealed that ranolazine (5μM), low-dose dronedarone (0.3μM), and the combination significantly prolonged action potential duration (APD90) in atrial myocytes from patients in sinus rhythm (prolongation by 23.5±0.1%, 31.7±0.1% and 25.6±0.1% respectively). Most importantly, in atrial myocytes from patients with AF ranolazine alone, but more the combination with dronedarone, also prolonged the typically abbreviated APD90 (prolongation by 21.6±0.1% and 31.9±0.1% respectively). It was clearly observed that neither ranolazine, dronedarone nor the combination significantly changed the APD or contractility and twitch force in ventricular myocytes or trabeculae from patients with heart failure (HF). Interestingly ranolazine, and more so the combination, but not dronedarone alone, caused hyperpolarization of the resting membrane potential in cardiomyocytes from AF. As measured by confocal microscopy (Fluo-3), ranolazine, dronedarone and the combination significantly suppressed diastolic sarcoplasmic reticulum (SR) Ca(2+) leak in myocytes from sinus rhythm (reduction by ranolazine: 89.0±30.7%, dronedarone: 75.6±27.4% and combination: 78.0±27.2%), in myocytes from AF (reduction by ranolazine: 67.6±33.7%, dronedarone: 86.5±31.7% and combination: 81.0±33.3%), as well as in myocytes from HF (reduction by ranolazine: 64.8±26.5% and dronedarone: 65.9±29.3%)., Conclusions: Electrophysiological measurements during exposure to ranolazine alone or in combination with low-dose dronedarone showed APD prolongation, cellular hyperpolarization and reduced SR Ca(2+) leak in human atrial myocytes. The combined inhibitory effects on various currents, in particular Na(+) and K(+) currents, may explain the anti-AF effects observed in the HARMONY trial. Therefore, the combination of ranolazine and dronedarone, but also ranolazine alone, may be promising new treatment options for AF, especially in patients with HF, and merit further clinical investigation., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Background: Chronic metformin treatment was found to reduce elevated thyrotropin levels. Amiodarone treatment is associated with a range of effects in thyroid function from mild derangements to overt thyroid dysfunction. No previous study has investigated the effect of metformin on hypothalamic-pituitary-thyroid axis activity in patients with amiodarone-induced hypothyroidism., Methods: The study included three age-, sex- and weight-matched groups of amiodarone-treated patients with type 2 diabetes: patients with treated overt hypothyroidism (group I, n=15), patients with untreated subclinical hypothyroidism (group II, n=15), and subjects without thyroid disorders (group III, n=18). The lipid profile, fasting plasma glucose levels, the homeostatic model assessment 1 of insulin resistance ratio (HOMA1-IR), glycated hemoglobin, the estimated glomerular filtration rate, as well as serum levels of thyrotropin, thyroid hormones, prolactin, insulin and insulin-like growth factor-1 (IGF-1) were assessed at baseline and after 6 months of metformin treatment (2.55-3g daily)., Results: In all groups of patients, metformin reduced plasma glucose and triglycerides, serum insulin, glycated hemoglobin as well as HOMA1-IR. The estimated glomerular filtration rate, thyroid hormones, prolactin and IGF-1 remained at a similar level throughout the study. In patients with untreated amiodarone-induced hypothyroidism, but not in the other groups of patients, metformin reduced serum levels of thyrotropin and this effect correlated weakly with its action on insulin sensitivity., Conclusions: The obtained results indicate that the effect of metformin on hypothalamic-pituitary-thyroid axis activity is partially related to thyroid function. Metformin treatment may bring clinical benefits to patients with amiodarone-induced hypothyroidism and poor tolerance of exogenous L-thyroxine., (Copyright © 2015 Institute of Pharmacology, Polish Academy of Sciences. Published by Elsevier Urban & Partner Sp. z o.o. All rights reserved.)

Electrical remodeling plays a pivotal role in maintaining the reentry during atrial fibrillation. In this study, we assessed influence of electrical remodeling on pharmacological manipulation of the atrial refractoriness in rabbits. We used an atrial electrical remodeling model of the rabbit, subjected to rapid atrial pacing (RAP; 600 beats/min) for 2-4 weeks, leading to shortening of atrial effective refractory period (AERP). Intravenous administration of dl-sotalol (6 mg/kg), bepridil (1 mg/kg), amiodarone (10 mg/kg) or vernakalant (3 mg/kg) significantly prolonged the AERP both in the control and RAP rabbits. The extents in the RAP rabbits were similar to those in the control animals. On the other hand, prolonging effects of intravenously administered ranolazine (10 mg/kg) or tertiapin-Q (0.03 mg/kg) on the AERP in the RAP rabbits were more potent than those in the control animals. These results suggest that rapid pacing-induced electrical remodeling effectively modified the prolonging effects of ranolazine and tertiapin-Q on the AERP in contrast to those of clinically available antiarrhythmic drugs, dl-sotalol, bepridil amiodarone and vernakalant., (Copyright © 2016 Japanese Pharmacological Society. Production and hosting by Elsevier B.V. All rights reserved.)

Early direct current (DC) shock is the most important therapy for ventricular fibrillation. Following the increased availability of automated external defibrillators (AED), the survival rate of cardiopulmonary arrest patients with ventricular fibrillation has improved. Although patients with shock-resistant ventricular fibrillation require additional antiarrhythmic drug therapy, the optimal protocol has not been established. Nifekalant is a pure potassium channel blocker with a pyrimidinedione structure. Nifekalant was approved in Japan for the treatment of life-threatening ventricular tachyarrhythmias in 1999, and is widely used as a class III antiarrhythmic intravenous drug. Intravenous amiodarone was approved in Japan in 2007, and exhibits various effects on ion channels, receptors, sympathetic activity, and thyroid function. Nifekalant and amiodarone also exhibit many pharmacological and pharmacodynamic differences. As nifekalant has no negative inotropic effect and a rapid action and clearance with a short half-life, it has some advantages over amiodarone for use in cardiopulmonary resuscitation. Indeed, data from clinical and animal studies suggest that nifekalant is superior to amiodarone for resuscitation of cardiopulmonary arrest resulting from shock-resistant ventricular fibrillation. A 300-mg bolus intravenous injection of amiodarone is considered an overdose for resuscitation of shock-resistant ventricular fibrillation. Further clinical studies are required to evaluate the effects of nifekalant compared with amiodarone, and to determine the optimal dose of amiodaone, for resuscitation of shock-resistant ventricular fibrillation.

Background: Several mammalian species display distinct biophysical properties between atrial and ventricular voltage-gated sodium current (INa); however, the potential mechanism behind this phenomenon is unknown., Objective: The purpose of this study was to investigate the potential molecular identities of the different INa in atrial and ventricular myocytes of rat hearts., Methods: Whole-cell patch voltage-clamp and molecular biology techniques were used in the study., Results: Ventricular INa exhibited a slower inactivation, more positive potential of inactivation, and quicker recovery from inactivation compared to atrial INa. Real-time polymerase chain reaction and western blot analysis revealed that mRNA and protein levels of NaVβ2 and NaVβ4 subunits, but not NaV1.5, were greater in ventricular myocytes than in atrial myocytes. INa in heterologous HEK 293 cell expression system with coexpressing hNaV1.5 and hNaVβ2/hNaVβ4 showed similar biophysical properties to ventricular INa. Greater protein expression of NaVβ2 and NaVβ4 subunits was also observed in human ventricles. Interestingly, pharmacologic study revealed that the antiarrhythmic drug dronedarone (10 μM) inhibited atrial INa more (by 73%) than ventricular INa (by 42%), and shifted its inactivation to more negative voltages (-4.6 mV) compared to ventricular INa., Conclusion: The results of this study demonstrate the novel information that the distinctive biophysical properties of INa in atrial and ventricular myocytes can be attributed to inhomogeneous expression of NaVβ2 and NaVβ4 subunits, and that atrial INa is more sensitive to inhibition by dronedarone., (Copyright © 2016 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.)

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.

Dronedarone is an antiarrhythmic agent approved in 2009 for the treatment of atrial fibrillation. An in-house preliminary study demonstrated that dronedarone inhibits cytochrome P450 (CYP) 3A4 and 3A5 in a time-dependent manner. This study aimed to investigate the inactivation of CYP450 by dronedarone. We demonstrated for the first time that both dronedarone and its main metabolite N-desbutyl dronedarone (NDBD) inactivate CYP3A4 and CYP3A5 in a time-, concentration-, and NADPH-dependent manner. For the inactivation of CYP3A4, the inactivator concentration at the half-maximum rate of inactivation and inactivation rate constant at an infinite inactivator concentration are 0.87 µM and 0.039 minute(-1), respectively, for dronedarone, and 6.24 µM and 0.099 minute(-1), respectively, for NDBD. For CYP3A5 inactivation, the inactivator concentration at the half-maximum rate of inactivation and inactivation rate constant at an infinite inactivator concentration are 2.19 µM and 0.0056 minute(-1) for dronedarone and 5.45 µM and 0.056 minute(-1) for NDBD. The partition ratios for the inactivation of CYP3A4 and CYP3A5 by dronedarone are 51.1 and 32.2, and the partition ratios for the inactivation of CYP3A4 and CYP3A5 by NDBD are 35.3 and 36.6. Testosterone protected both CYP3A4 and CYP3A5 from inactivation by dronedarone and NDBD. Although the presence of Soret peak confirmed the formation of a quasi-irreversible metabolite-intermediate complex between dronedarone/NDBD and CYP3A4/CYP3A5, partial recovery of enzyme activity by potassium ferricyanide illuminated an alternative irreversible mechanism-based inactivation (MBI). MBI of CYP3A4 and CYP3A5 was further supported by the discovery of glutathione adducts derived from the quinone oxime intermediates of dronedarone and NDBD. In conclusion, dronedarone and NDBD inactivate CYP3A4 and CYP3A5 via unique dual mechanisms of MBI and formation of the metabolite-intermediate complex. Our novel findings contribute new knowledge for future investigation of the underlying mechanisms associated with dronedarone-induced hepatotoxicity and clinical drug-drug interactions., (Copyright © 2015 by The American Society for Pharmacology and Experimental Therapeutics.)