Ten years of experience with amiodarone

Argentina's most important contributions in the field of electrophysiology

Latin American electrocardiology emerged internationally thanks to the Argentine School of Electrocardiology. All started when the idea of a different anatomy of the conduction system was not only necessary to change the paradigm of a bifascicular system, but also to question diagnostic electrocardiographic criteria adopted by the scientific community without dispute. Almost every scientific contribution coming from the Argentine School of Electrocardiology represented a significant step forward in the understanding of the electrophysiology of the heart and its electrocardiographic counterpart. There is another reason that increases their value: the noticeable simplicity of the technical facilities with which these studies were done from the modest laboratory in Argentina, whose production was purely and genuinely Latin American. In the following lines we summarize what we consider to be the greatest contributions of the Argentine school to world electrophysiology.

Thyroid Dysfunction under Amiodarone in Patients with and without Congenital Heart Disease: Results of a Nationwide Analysis

Background: Amiodarone has a profound adverse toxicity profile. Large population-based analyses quantifying the risk of thyroid dysfunction (TD) in adults with and without congenital heart disease (ACHD) are lacking. Methods: All adults registered with a major German health insurer (≈9.2 million members) with amiodarone prescriptions were analyzed. Occurrence of amiodarone-associated TD was assessed. Results: Overall, 48,891 non-ACHD (37% female; median 73 years) and 886 ACHD (34% female; median 66 years) received amiodarone. Over 184,787 patient-years, 10,875 cases of TD occurred. The 10-year risk for TD was 38% in non-ACHD (35% ACHD). Within ACHD, compared to amiodarone-naïve patients, the hazard ratio (HR) for TD was 3.9 at 4 years after any amiodarone exposure. TD was associated with female gender (HR 1.42, p < 0.001) and younger age (HR 0.97 per 10 years, p = 0.009). Patients with congenital heart disease were not at increased risk (HR 0.98, p = 0.80). Diagnosis of complex congenital heart disease, however, was a predictor for TD (HR 1.56, p = 0.02). Amiodarone was continued in 47% of non-ACHD (38% ACHD), and 2.3% of non-ACHD (3.5% ACHD) underwent thyroid surgery/radiotherapy. Conclusions: Amiodarone-associated TD is common and comparable in non-ACHD and ACHD. While female gender and younger age are predictors for TD, congenital heart disease is not necessarily associated with an elevated risk.

Amiodarone and thyroid physiology, pathophysiology, diagnosis and management

Although amiodarone is considered the most effective antiarrhythmic agent, its use is limited by a wide variety of potential toxicities. The purpose of this review is to provide a comprehensive "bench to bedside" overview of the ways amiodarone influences thyroid function. We performed a systematic search of MEDLINE to identify peer-reviewed clinical trials, randomized controlled trials, meta-analyses, and other clinically relevant studies. The search was limited to English-language reports published between 1950 and 2017. Amiodarone was searched using the terms adverse effects, hypothyroidism, myxedema, hyperthyroidism, thyroid storm, atrial fibrillation, ventricular arrhythmia, and electrical storm. Google and Google scholar as well as bibliographies of identified articles were reviewed for additional references. We included 163 germane references in this review. Because amiodarone is one of the most frequently prescribed antiarrhythmic drugs in the United States, the mechanistic, diagnostic and therapeutic information provided is relevant for practicing clinicians in a wide range of medical specialties.

Identification of the antiarrhythmic drugs amiodarone and lorcainide as potent H3 histamine receptor inverse agonists

Use of molecular pharmacology to reprofile older drugs discovered before the advent of recombinant technologies is a fruitful method to elucidate mechanisms of drug action, expand understanding of structure-activity relationships between drugs and receptors, and in some cases, repurpose approved drugs. The H3 histamine receptor is a G-protein-coupled receptor (GPCR) primarily expressed in the central nervous system where among many things it modulates cognitive processes, nociception, feeding and drinking behavior, and sleep/wakefulness. In binding assays and functional screens of the H3 histamine receptor, the antiarrhythmic drugs lorcainide and amiodarone were identified as potent, selective antagonists/inverse agonists of human and rat H3 histamine receptors, with relatively little or no activity at over 20 other monoamine GPCRs, including H1, H2, and H4 receptors. Potent antagonism of H3 receptors was unique to amiodarone and lorcainide of 20 antiarrhythmic drugs tested, representing six pharmacological classes. These results expand the pharmacophore of H3 histamine receptor antagonist/inverse agonists and may explain, in part, the effects of lorcainide on sleep in humans.

Specific chemotherapy of Chagas disease: relevance, current limitations and new approaches

A critical review of the development of specific chemotherapeutic approaches for the management of American Trypanosomiasis or Chagas disease is presented, including controversies on the pathogenesis of the disease, the initial efforts that led to the development of currently available drugs (nifurtimox and benznidazole), limitations of these therapies and novel approaches for the development of anti-Trypanosoma cruzi drugs, based on our growing understanding of the biology of this parasite. Among the later, the most promising approaches are ergosterol biosynthesis inhibitors such as posaconazole and ravuconazole, poised to enter clinical trials for chronic Chagas disease in the short term; inhibitors of cruzipain, the main cysteine protease of T. cruzi, essential for its survival and proliferation in vitro and in vivo; bisphosphonates, metabolic stable pyrophosphate analogs that have trypanocidal activity through the inhibition of the parasite's farnesyl-pyrophosphate synthase or hexokinase; inhibitors of trypanothione synthesis and redox metabolism and inhibitors of hypoxanthine-guanine phosphoribosyl-transferase, an essential enzyme for purine salvage in T. cruzi and related organisms. Finally, the economic and political challenges faced by development of drugs for the treatment of neglected tropical diseases, which afflict almost exclusively poor populations in developing countries, are analyzed and recent potential solutions for this conundrum are discussed.

Nanotechnological approaches against Chagas disease

Over several thousand years, the flagellated Trypanosome cruzi-causative agent of Chagas disease-developed a complex life cycle between the reduviidae vectors and its human hosts. Due to their silent and hidden location, the intracellular amastigotes are mainly responsible for the nearly 50,000 annual deaths caused by the chronic chagasic cardiomyopathy. Chagas disease is the most important parasitic disease in the Americas, though treatments have not evolved towards a more efficient pharmacotherapy that (i) eradicates the scarce amastigotes present at the indeterminate/chronic form and (ii) employs less toxic drugs than benznidazole or nifurtimox. Nano-drug delivery systems (nanoDDS) represent useful means to selectively deliver the drug to intracellular targets. However, preclinical research in Chagas must be extended in order to improve the chances of a clinical implementation. The stages involved in this process are (i) selection of the appropriate drug for a specific parasite, (ii) development of a drug-loaded nanoDDS structure that displays the adequate pharmacokinetics, biodistribution and intracellular transit and (iii) selection of the right parasite form to target and the right stage of the disease for the treatment to be started. In this review we will critically overview the few research works published in the last 20years in the context of nanotechnology and Chagas diseases and highlight the gaps in knowledge towards the design of more efficient medicines to address this endemic.

Ergosterol biosynthesis and drug development for Chagas disease

This article presents an overview of the currently available drugs nifurtimox (NFX) and benznidazole (BZN) used against Trypanosoma cruzi, the aetiological agent of Chagas disease; herein we discuss their limitations along with potential alternatives with a focus on ergosterol biosynthesis inhibitors (EBI). These compounds are currently the most advanced candidates for new anti-T. cruzi agents given that they block de novo production of 24-alkyl-sterols, which are essential for parasite survival and cannot be replaced by a host's own cholesterol. Among these compounds, new triazole derivatives that inhibit the parasite's C14alpha sterol demethylase are the most promising, as they have been shown to have curative activity in murine models of acute and chronic Chagas disease and are active against NFX and BZN-resistant T. cruzi strains; among this class of compounds, posaconazole (Schering-Plough Research Institute) and ravuconazole (Eisai Company) are poised for clinical trials in Chagas disease patients in the short term. Other T. cruzi-specific EBI, with in vitro and in vivo potency, include squalene synthase, lanosterol synthase and squalene epoxidase-inhibitors as well as compounds with dual mechanisms of action (ergosterol biosynthesis inhibition and free radical generation), but they are less advanced in their development process. The main putative advantages of EBI over currently available therapies include their higher potency and selectivity in both acute and chronic infections, activity against NFX and BZN-resistant T. cruzi strains, and much better tolerability and safety profiles. Limitations may include complexity and cost of manufacture of the new compounds. As for any new drug, such compounds will require extensive clinical testing before being introduced for clinical use, and the complexity of such studies, particularly in chronic patients, will be compounded by the current limitations in the verification of true parasitological cures for T. cruzi infections.

Involvement of thymus in amiodarone-treated autoimmune myocarditis in rats

We previously showed that amiodarone, an iodine-rich benzofuranic derivative, interferes with the progression of myocarditis using a rat model of experimental autoimmune myocarditis. Further studies have also revealed that intraperitoneal treatment with 12.5 mg/kg amiodarone, which is below the range of its therapeutic plasma concentration, also effectively interferes with the progression of myocarditis using the same model. The relationship between myocarditis and the thymus has not been studied in either patients or animal models. To investigate whether the thymus is involved in the effect of amiodarone on experimental autoimmune myocarditis, we examined its phenotypic distribution in thymocytes and peripheral blood lymphocytes using flow cytometry. We found no significant differences in the proportions of CD4(+) and CD8(+) T cells and the CD4(+)/CD8(+) T cell ratio in the control group compared with amiodarone-treated group. However, amiodarone-treated group induced a decrease in the proportion of CD4(+)TNF(+) and CD4(+)IL-4(+) T cells and an increase in CD4(+)IFN(+) T cells, resulting in a significant reduction of the CD4(+)TNF(+)/CD4(+)IFN(+) and CD4(+)IL-4(+)/CD4(+)IFN(+) T cell ratios. These results suggest for the first time that the thymus is actively involved when myocarditis is treated with amiodarone.

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.

High-dosage continuous amiodarone therapy to treat new-onset supraventricular tachyarrhythmias in surgical intensive care patients: an observational study

BACKGROUND

New-onset supraventricular tachyarrhythmias (SVTA) are a complication contributing significantly to morbidity and mortality in surgical intensive care unit (SICU) patients. Although only few data on efficiency can be found in the literature, class III antiarrhythmics have become popular in the treatment of SVTA in critically ill patients.

SETTING

12-bed general and surgical ICU in a university teaching hospital.

DESIGN

Observational, retrospective study.

PATIENTS

131 SICU patients with SVTA (narrow-complex non-sinus tachyarrhythmias with heart rates > or = 100 bpm).

INTERVENTION

High-dosage amiodarone infusion according to an institutional protocol.

MEASUREMENTS

Hemodynamic data, acid-base status, and single organ functions were obtained in all patients before amiodarone infusion and at 12, 24, and 48 hours afterwards. Patients were divided into responders and nonresponders. Amiodarone infusion (mean dosage 24 h: 1625+/-528 mg; 48 h: 2708+/-895 mg) restored sinus rhythm in 54% of study patients within 12 h, in 64% within 24 h, and in 75% within 48 h. Heart rate, central venous pressure, and milrinone requirements significantly decreased in all patients; this was accompanied by a significant increase in stroke-volume index and mean arterial pressure. Serum concentrations of creatinine and bilirubin increased in all patients.

CONCLUSION

High-dosage continuous amiodarone infusion during a period of 48 hours resulted in restoration of SR in 75% of SICU patients with new-onset SVTA and moderate to severe multiple-organ dysfunction syndrome. A significant improvement in cardiocirculatory function was more pronounced in responders but could be demonstrated irrespective of restoration of sinus rhythm in all patients. Apart from a possibly amiodarone-mediated increase in concentrations of creatinine and bilirubin, no major drug-related adverse effects occurred during the observation period.

Beneficial effects of amiodarone and dronedarone (SR 33589b), when applied during low-flow ischemia, on arrhythmia and functional parameters asssessed during reperfusion in isolated rat hearts

The effects of short-term amiodarone and dronedarone treatments on action potential characteristics and arrhythmia (ventricular tachycardia ) induced by reperfusion after global low-flow ischemia were studied in rat hearts. The actions of amiodarone and SR on recovery of coronary flow and contractile function were also determined. Isolated hearts were stabilized for 40 min and were then submitted to 25-min global low-flow ischemia (constant coronary flow, 0.3 ml/min) followed by 30 min of reperfusion at constant pressure. Drugs were applied only during ischemia: consequently, action potential duration (APD) tended to widen. During reperfusion, APD tended to recover or shorten, and the more complete the recovery, the less the arrhythmia. Despite its ability to widen APD during ischemia, amiodarone facilitated APD recovery during reperfusion. Moreover, APD shortening and ventricular tachycardia suppression exhibit a bell-shaped concentration-response relation, implying that the drugs affect ventricular tachycardia by a class III-independent action. These results point to an anti-ischemic action supported by improvement in function and inhibition of reactive hyperemia.

The effect of amiodarone on the beta-adrenergic receptor is due to a downregulation of receptor protein and not to a receptor-ligand interaction

Downregulation of beta adrenergic receptors (beta-AR) by amiodarone (Am) have been reported in several studies both in vivo and in vitro. The mechanism underlying the antiadrenergic effect of Am is, however, still unclear. The aim of this study was to characterize whether the antiadrenergic effect of amiodarone is due to binding to the beta-AR or to downregulation of the beta-AR receptor protein. All experiments were performed on confluent mouse AT-1 cardiomyocytes cultured for 6 days. In acute experiments, equilibrium binding with [3H]-CGP-12177 to beta-AR was not directly inhibited by Am and the equilibrium binding constant did not change during prolonged exposure up to 72 hours. After Am exposure for 48 hours beta-AR density was decreased by 26% (p<0.005). T3 partially prevented the downregulation elicited by Am (p<0.05). A Western blot analysis with beta1-AR antibodies revealed a decreased signal intensity in cells treated with Am for 48 h as compared to control (p<0.05). Isoproterenol-provoked cAMP response did not change after acute exposure to Am. After incubation for 48 hours with Am there was, however, a 20% decrease in cAMP response as compared to control (p<0.05). This study shows that the effect of Am on beta-AR is due to a downregulation of the beta-AR protein and not to a competitive or non-competitive receptor-ligand interaction. This indicates a new pharmacological mechanism for modulation of beta-AR, which probably is transcriptionally regulated.

Electrical cardioversion after amiodarone administration

The possible effect of amiodarone administration on the effectiveness and complications of electrical cardioversion of supraventricular tachyarrhythmias has not been properly assessed. To investigate the effects of amiodarone on cardioversion, we performed 130 electrical cardioversion procedures in 116 patients who were receiving long-term amiodarone therapy (group I) and 44 cardioversion procedures in 43 patients who were receiving intravenous infusions of amiodarone (group II). All patients in groups I and II had atrial fibrillation or flutter. In group I, there was a higher incidence of ventricular premature beats than in a control group of patients who underwent 100 cardioversions; one patient had severe bradycardia with asystole, which was resolved satisfactorily. In group II there was a higher incidence of sinus bradycardia and ventricular premature beats. It was concluded that electrical cardioversion of supraventricular arrhythmias can be safely performed in patients who are receiving long-term oral or intravenous amiodarone therapy if the usual precautions are observed.

Amiodarone. An overview of its pharmacological properties, and review of its therapeutic use in cardiac arrhythmias

Amiodarone, originally developed over 20 years ago, is a potent antiarrhythmic drug with the actions of all antiarrhythmic drug classes. It has been successfully used in the treatment of symptomatic and life-threatening ventricular arrhythmias and symptomatic supraventricular arrhythmias. In patients with left ventricular dysfunction amiodarone does not usually produce any clinically significant cardiodepression and the drug has relatively high antiarrhythmic efficacy. Preliminary studies indicate that amiodarone may have a beneficial effect on mortality and survival in certain groups of patients with ventricular arrhythmias, an action probably related to both its antiarrhythmic and antifibrillatory effects. The adverse effect profile of amiodarone is diverse, involving the cardiac, thyroid, pulmonary, hepatic, gastrointestinal, ocular, neurological and dermatological systems. Interstitial pneumonitis and hepatitis are potentially fatal, but the vast majority of adverse events are less serious, and some may be dose dependent. Pretreatment monitoring, regular assessments and the use of minimum effective doses are, therefore, necessary. Thus, with appropriate monitoring to control its well recognised adverse effects amiodarone has an important place as an effective 'broad spectrum' antiarrhythmic drug which has, so far, been used when other treatments have proved ineffective. More recent preliminary data also suggest that it may also have a beneficial effect in the prevention of sudden death in some patients.

Amiodarone- and desethylamiodarone-induced pulmonary phospholipidosis, inhibition of phospholipases in vivo, and alteration of [14C]amiodarone uptake by perfused lung

Amiodarone (AM) pulmonary phospholipidosis in patients receiving this drug is well recognized. We investigated the in vivo phospholipidosis-inducing potency of AM and its major nonpolar metabolite, desethylamiodarone (DEA), in rats, their ability to inhibit phospholipases, and also the effects on pulmonary uptake of [14C] AM. Fisher-344 male rats (200 to 250 g) were given AM or DEA (100 mg/kg/d orally) for 2, 7, or 21 d. Food consumption and body weight gain were significantly reduced by both AM and DEA treatment. The control rats, therefore, were pair-fed. Both drugs increased the number of cells in lavage during the treatment. Lung/body weight ratio increased after 21 d of treatment in AM rats. Mortality increased to 100% by day 10 in DEA-treated rats, unlike in AM-treated rats, where 20 to 30% of the animals died during this period and thereafter. No further mortality occurred during 21 d of treatment. Levels of phospholipids increased in lavaged lung, alveolar lavage cells, and surfactant material in AM- as well as DEA-treated rats. However, there was no significant difference between the two treatment groups. Phospholipases A and C were measured in lysosomal soluble fractions of lavaged lung and sonicated lung lavage cells. Both drugs exerted inhibitory action on phospholipases in the lavage cells but, to some extent, spared phospholipases in lysosomal plus mitochondrial soluble fraction isolated from lavaged lung with reversibility in enzyme inhibition despite continuous treatment. [14C] AM uptake by perfused lung, lavage cells as well as surfactant supernatant was increased in AM- and DEA-treated rats. Again, increase in pulmonary uptake of [14C]AM was similar in AM- and DEA-treated rats. These results thus suggest: (1) DEA is more toxic to rats than is AM, at the dose level used. The ability to sequester AM and the parameters related to phospholipidosis revealed no significant differences between these two analogs. (2) Both drugs are inhibitors of lavage cell phospholipases and also are inhibitory to lung lysosomal phospholipases to a lesser extent. Recovery of lung phospholipases occurred despite continuous treatment. (3) AM- and DEA-induced phospholipidosis increased the uptake of [14C]AM by perfused lung. (4) The mechanism of AM-induced pulmonary phospholipidosis includes selective in vivo inhibition of phospholipases.

Side effects from amiodarone

Amiodarone causes many side effects involving all organ systems. Although most of the side effects are mild and do not limit the use of the drug, there are several that are serious. Since many of these toxic reactions develop only after a prolonged period of therapy, careful follow-up on a regular basis is essential.

Rapid control of refractory atrial tachyarrhythmias with high-dose oral amiodarone

To shorten the delay in the onset of antiarrhythmic effect when using amiodarone for the conversion of refractory atrial tachyarrhythmias to sinus rhythm, 19 patients were given oral amiodarone according to a high-dose loading protocol. In 18 of 19 patients (95%), sinus rhythm was restored 36 hours (range, 0 to 96 hours) after starting amiodarone. The conversion occurred as a result of amiodarone therapy alone within 48 hours in 12 patients (63%), and by amiodarone therapy plus electrical cardioversion at 48 to 96 hours in six patients (32%). Minor side effects were noted in eight patients (42%). No major side effects were encountered. The length of hospital stay after initiating amiodarone therapy was 3.6 days (range, 2 to 5 days). High-dose oral amiodarone loading is a safe and effective method for the rapid conversion of atrial tachyarrhythmias to sinus rhythm.

Class III antiarrhythmic action linked with positive inotropy: acute electrophysiological and inotropic effects of amiodarone in vitro

Negative inotropy is an adverse feature of most antiarrhythmic drugs. Positive inotropy, however, has been demonstrated for some drugs with class III antiarrhythmic action. Although amiodarone exerts its antiarrhythmic effect by an interplay of different actions on cardiac cells, it has been regarded to be the prototype class III drug due to its prolongation of action potential duration. The present study was designed to test the hypothesis that class III antiarrhythmic action and positive inotropy may be linked. We compared the effects of amiodarone in Cordarone and its solvent Tween 80 on automaticity, refractoriness and inotropy. Two series of experiments were done; one with spontaneously beating rat atria to study the effects on sinus node function, and one with electrically stimulated left atria to study the effects on excitability, refractoriness and inotropy. Amiodarone 1 x 10(-4) M decreased spontaneous heart rate by 13% and prolonged sinus node recovery time by 105%. Without affecting the excitability amiodarone prolonged the effective refractory period by 12%. At the same time contractile force increased by 12%. Lower concentration of amiodarone (5 x 10(-6) M) or Tween 80 had no significant effects. In conclusion, amiodarone exerts acute electrophysiological and inotropic effects in vitro. The class III antiarrhythmic action of amiodarone is linked with positive inotropy.

Adverse effects of amiodarone. Pathogenesis, incidence and management

Amiodarone is an extremely effective antiarrhythmic agent for the treatment of both life-threatening ventricular arrhythmias and refractory supraventricular tachyarrhythmias. Subjective minor side effects are common with amiodarone but rarely require discontinuation of therapy and are often handled by dose reduction. Serious end-organ toxicity, including pulmonary fibrosis and drug-induced hepatitis, have been the most common indications for discontinuing amiodarone therapy in these patients.

Effects of propafenone on ventricular arrhythmias: double-blind, parallel, randomized, placebo-controlled dose-ranging study

Propafenone is a new class Ic antiarrhythmic compound with a broad pharmacologic profile. In this study, its dose-response relationship was examined in a double-blind, randomized, placebo-controlled five treatment parallel design protocol. Patients enrolled had heart disease with Lown grade 2 premature ventricular contractions (PVCs) (greater than or equal to 30/hr) documented on 24-hour Holter recordings. Propafenone was compared in four doses (337.5, 450, 675, and 900 mg/day) to placebo. The double-blind phase lasted 2 weeks. Two hundred twenty-six patients were enrolled, of whom 171 were men and 55 were women; their mean age was 59.8 years and 85% were Caucasian and 4% were black. The arrhythmias were symptomatic in 173. Twenty (8.8%) withdrew from the study before completion: 15 had adverse reactions, two had intercurrent illnesses, and three withdrew for administrative reasons. In one patient, the density of arrhythmia appeared to increase with propafenone. Side effects were of central nervous system or gastrointestinal origin; less than 5% of patients developed first-degree atrioventricular block or intraventricular conduction defect. There were no deaths in the study. The occurrence of side effects was not related to dose. Propafenone had no effect on heart rate. It increased the PR interval at all doses (9% to 22% compared to placebo at baseline; p less than 0.01) at 450 to 900 mg/day after 2 weeks of therapy. The drug increased the QRS duration at all doses, highly significantly at 675 mg/day (8.5 msec; p less than 0.01) and at 900 mg/day (15.7 msec; p less than 0.01) after 2 weeks of therapy. Only at the highest dose was the QTc slightly but significantly (14.3 msec; p less than 0.01) increased. Propafenone exerted a dose-dependent effect on PVCs recorded on serial 24-hour Holter recordings: compared to placebo, at 2 weeks 337.5 mg/day reduced PVCs by 70.8% (p less than 0.05), 450 mg/day reduced PVCs by 82.0% (p less than 0.01), 675 mg/day reduced PVCs by 90.2% (p less than 0.01) and 900 mg/day reduced PVCs by 95.3% (p less than 0.01). The effects of the two highest doses of propafenone were significantly greater than those of 337.5 mg/day. In 68% of the patients receiving 900 mg/day, 80% or greater reduction in total PVCs was found. In addition, there was a greater than 90% decrease in ventricular couplets, and 96% decrease in ventricular tachycardia (VT) beats. Propafenone eliminated PVCs in 8% of all patients, ventricular couplets in 58%, and VT beats in 91%.(ABSTRACT TRUNCATED AT 400 WORDS)

Right and left ventricular function during chronic amiodarone therapy

Although chronic therapy with amiodarone is an effective means of suppressing ventricular tachycardia, its long-term effects on ventricular function have not been evaluated. Therefore, left ventricular (LV) and right ventricular (RV) ejection fraction (EF) as well as wall motion score were assessed in 21 patients with ventricular tachycardia before therapy and after 2, 6, 10 and 20 weeks of amiodarone therapy. Serum amiodarone levels after 2, 6, 10 and 20 weeks were 1.9 +/- 0.7, 1.7 +/- 0.6, 1.5 +/- 0.6 and 1.5 +/- 0.7 micrograms/ml, respectively. Drug therapy did not significantly affect the mean LVEF (0 weeks 38 +/- 17, 2 weeks 40 +/- 17, 6 weeks 40 +/- 17, 10 weeks 41 +/- 18 and 20 weeks 40 +/- 18%) or the mean RVEF. Neither LV wall motion score nor RV wall motion score were changed significantly during amiodarone therapy. Fourteen patients had a drug-free LVEF less than 40% (mean 28 +/- 7%). Ventricular function in this subgroup was not impaired after 20 weeks of amiodarone therapy (drug-free LVEF 28 +/- 7%, 20 weeks LVEF 29 +/- 9%; drug-free RVEF 42 +/- 13%, 20 weeks RVEF 41 +/- 12%). Ten patients who were evaluated 34 +/- 6 months after initiation of amiodarone therapy had no significant change in LVEF (drug-free 37 +/- 20%, 34 months 43 +/- 20%). Ventricular functional reserve was assessed after 20 weeks of therapy.(ABSTRACT TRUNCATED AT 250 WORDS)

Empiric amiodarone versus "ineffective" drug therapy in patients with refractory ventricular tachyarrhythmias

Because of its presumed unique efficacy, amiodarone (AM) is often used to treat patients whose sustained ventricular tachyarrhythmias (VT/VF) appear to be drug-refractory. To examine the efficacy of AM in such patients, we performed a retrospective analysis of 77 patients with drug-refractory VT/VF treated with either empiric AM or with drugs predicted during electrophysiological (EP) testing to be ineffective (ID). To qualify for the study, patients had to have spontaneous, symptomatic VT/VF, and persistently inducible VT during serial EP testing with drugs. All 77 patients were offered therapy with AM. Those who refused were treated with ID, whenever possible, an ID was selected which "improved" the EP study compared to baseline. Originally, 68 patients elected AM and nine elected ID. Because of drug intolerance or inefficacy, 10 patients crossed over during the course of the study; a total of 71 patients were followed on AM for 15.7 +/- 11.0 months, and 16 on ID for 17.8 +/- 10.8 months (mean +/- SD). During follow-up, the cumulative recurrence of VT/VF at 6, 12, and 24 months for AM versus ID was 16 +/- 5% versus 44 + 12% (P less than 0.002), 32 +/- 6% versus 44 +/- 12% (NS), and 41 +/- 7% versus 44 +/- 12% (NS) (+/- SE). The recurrence of VT was significantly lower in the AM group only for the first 6 months of therapy.(ABSTRACT TRUNCATED AT 250 WORDS)

Amiodarone-induced hepatic phospholipidosis: correlation of morphological and biochemical findings in an animal model

Morphological and biochemical investigations were performed in guinea pigs after 1, 3, 5 and 16 weeks of amiodarone feeding. The most prominent morphological finding was an increase in dense bodies in hepatocytes, Kupffer cells and in bile duct epithelia, reaching a maximum after 5 weeks of treatment according to morphometric analysis. Similar time courses were observed for the serum and liver tissue concentrations of amiodarone and desethylamiodarone and the--albeit minimal--extent of hepatocellular necrosis. Phospholipids in the liver homogenate were unchanged after 1 week, but significantly increased after prolonged amiodarone treatment. There was no significant alteration in the pattern of individual phospholipids. Serum and tissue concentrations as well as the extent of phospholipidosis do not appear to be a function of the duration of drug application. A very close correlation, however, was observed between the liver tissue concentration of amiodarone and the amount of dense bodies as a morphological expression of phospholipidosis.

Atenolol and amiodarone: a comparative study of their anti-ischaemic effect

A total of 10 patients with mixed angina were entered into a study to compare the anti-ischaemic efficacy of atenolol and amiodarone. The study was divided into three parts: (a) placebo for 2 weeks; (b) 100 mg atenolol given for 8 weeks; and (c) amiodarone given for 8 weeks, divided into week 1, 200 mg three times daily; week 2, 200 mg twice daily; weeks 3 and 4, 200 mg once daily; weeks 5-8, 200 mg once daily for 5 days a week. Clinical examination, basal and multi-stage effort electrocardiograms were performed at the end of each treatment. The number of anginal attacks and the amount of trinitrin taken by the patients were significantly reduced by both drugs with no significant difference between them. Compared with placebo, both drugs induced a significant increase in work capacity and in the time to decrease the ST-segment by 1 mm. At rest, atenolol reduced systolic blood pressure, heart rate and the systolic blood pressure--heart rate product compared with placebo. Systolic blood pressure was also reduced significantly compared with patients given amiodarone. Amiodarone did not influence these parameters. At maximum effort, amiodarone reduced heart rate and the systolic blood pressure--heart rate product compared with placebo. This reduction was greater for atenolol. The ST-segment depression was comparable between patients given either test drug. Amiodarone, therefore, exerts an anti-ischaemic effect similar to that shown by atenolol with different haemodynamics: atenolol reducing myocardial oxygen demand, amiodarone having an additive increase of coronary flow. Such an effect was obtained with a lower dose of amiodarone than is commonly used.

Electrophysiologic effects of desethylamiodarone, an active metabolite of amiodarone: comparison with amiodarone during chronic administration in rabbits

During acute superfusion studies by means of the standard microelectrode technique, we previously showed that both amiodarone and its major metabolite, desethylamiodarone, had a modest effect on the lengthening of the action potential duration (APD) at high drug concentrations and produced a rate-dependent block of the sodium channel in cardiac muscle. In this study the comparative electrophysiologic effects of the two compounds in rabbits treated chronically with these compounds were determined with particular reference to repolarization and sinus node automaticity. The changes were correlated with those in serum and tissue drug levels and in thyroid hormone indices. After 1 week neither compound had a significant effect on atrial or sinus nodal potentials; after 3 weeks, amiodarone increased the atrial APD at 90% repolarization time by 10.5% (p less than 0.05) and the effective refractory period (ERP) by 6.7% (p less than 0.05). The corresponding figures for desethylamiodarone were 13% (NS) and 18% (NS). The sinus cycle length was increased 12% (NS) by amiodarone and 27.9% (p less than 0.05) after the metabolite. In animals treated for 6 weeks, amiodarone increased the ventricular APD at 90% repolarization by 58.8% (p less than 0.01) and desethylamiodarone by 42.0% the corresponding figures for the ERP were 63.4% (p less than 0.01 and 47.4% (p less than 0.01), respectively. At the stimulation frequency used, neither compound exerted a significant effect on Vmax. Both amiodarone and desethylamiodarone significantly decreased serum triiodothyronine and increased reverse triiodothyronine levels but had no effect on thyroxine.(ABSTRACT TRUNCATED AT 250 WORDS)

Amiodarone pharmacokinetics. II. Disposition kinetics following subchronic administration in rats

A 30 mg kg-1 intravenous bolus of 14C-amiodarone (19 microCi kg-1) was given to male Sprague-Dawley rats pretreated with 0 (vehicle), 25 or 100 mg kg-1 day-1 of amiodarone HCl orally for 37-42 days to determine the effects of dose and duration of administration on the disposition kinetics of amiodarone. Serial blood samples and total urine were collected over 48 hours and assayed for 14C-amiodarone by liquid scintillation counting following separation by HPLC. In all three groups, the blood 14C-amiodarone concentration-time curves declined bioexponentially with terminal half-lives (t1/2 beta) ranging from 14-22 hours. No differences in beta, t1/2 beta, or central compartment volume (Vc) were observed between the three groups of rats. In the rats pretreated with 100 mg kg-1 day-1 of amiodarone HCl for 5-6 weeks, amiodarone clearance (CL) and steady state volume of distribution (Vss) were reduced 52 per cent (12.2 to 5.9 ml min-1 kg-1) and 41 per cent (11.73 to 6.97 l kg-1), respectively. At the lower amiodarone daily dose, no changes in CL or Vss were observed. Negligible levels of radioactivity were detected in the urine. Amiodarone accounted for approximately 30-40 per cent of the total radioactivity in each blood specimen. This study demonstrated that CL and Vss were dose-dependent, and that beta, t1/2 beta and Vc were dose-independent. The results further suggested that the disposition kinetics of amiodarone were independent of the duration of drug administration.

Development of congestive heart failure and alterations in left ventricular function in patients with sustained ventricular tachyarrhythmias treated with amiodarone

The interaction between the efficacy and tolerance of amiodarone and the degree of left ventricular (LV) dysfunction was assessed in 126 patients with sustained ventricular tachyarrhythmias. In all patients radionuclide angiographic LV ejection fraction (EF) was measured before and after 8 to 12 months of amiodarone therapy. At baseline mean EF was 25 +/- 13% and 86 patients had an EF of 30% or less. In patients receiving amiodarone at steady state, there was a small but significant increase in EF (23 to 26%, p less than 0.05). Congestive heart failure (CHF) was present in 43 patients before amiodarone therapy. In 16 patients new (9 patients) or worsened (7 patients) CHF developed during the first year of amiodarone therapy. Development of CHF was not consistently related to a change in EF or heart rate. The clinical efficacy and tolerance of amiodarone were affected by the baseline EF and development of CHF. Efficacy and tolerance was 80% in patients with an EF of more than 30% and 60% in those with an EF of 30% or less. Among the 16 patients in whom new or worsened CHF developed, 6 (38%) died and 9 (56%) had recurrent ventricular tachyarrhythmias. Both baseline EF and development of CHF during amiodarone treatment significantly affect the prognosis in patients with ventricular tachyarrhythmias.

Comparison of survival of amiodarone-treated patients with coronary artery disease and malignant ventricular arrhythmias with that of a control group with coronary artery disease

Although amiodarone is effective in the treatment of ventricular arrhythmias, it is associated with serious toxic effects. In addition, the prognosis of patients with malignant ventricular arrhythmias and coronary artery disease treated with amiodarone remains poor. The survival of 54 consecutive patients with angiographically documented coronary artery disease and symptomatic ventricular tachycardia or ventricular fibrillation treated with amiodarone was compared with that of 5,125 medically treated patients with coronary artery disease. The amiodarone group was older, with worse left ventricular function and more peripheral and cerebrovascular disease. The 1 year survival probability was 0.73 for the amiodarone group and 0.94 for the control coronary artery disease group. At 2 years of follow-up, the survival probabilities were 0.60 and 0.90 for the amiodarone and the control group, respectively. When the survival curves were adjusted for group differences in baseline prognostic characteristics (integrated as a previously published hazard score), there was no difference in the prognosis of the two groups. These findings suggest that treatment with amiodarone of malignant ventricular arrhythmias associated with coronary artery disease maintains patients on an underlying survival curve determined by the degree of myocardial dysfunction, clinical characteristics and coronary anatomy, and that amiodarone does not have a deleterious effect on survival.

Comparative electrophysiologic effects of intravenous amiodarone and desethylamiodarone in dogs: evidence for clinically relevant activity of the metabolite

It has been suggested that some of the effects of long-term amiodarone therapy may be due to accumulation of a metabolite, desethylamiodarone. To evaluate the pharmacologic actions of the metabolite, we gave single intravenous doses (10 or 25 mg/kg) of amiodarone or desethylamiodarone to anesthetized dogs. The resulting plasma and myocardial concentrations of both agents were similar to levels achieved with long-term oral amiodarone therapy in man. Amiodarone and desethylamiodarone produced frequency-dependent slowing in ventricular and atrioventricular nodal conduction and increased atrial and ventricular refractory periods. The relative effects of these agents on fast- and slow-channel tissues differed, with amiodarone producing significantly greater prolongation of Wenckebach cycle length and desethylamiodarone producing larger increases in QRS duration, atrial refractory period, and ventricular refractory period. We conclude that desethylamiodarone has substantial electrophysiologic effects at clinically relevant concentrations and has relatively greater effect on fast-channel tissue in vivo than does amiodarone. The accumulation of desethylamiodarone probably accounts for some of the delayed electrophysiologic effects in patients receiving long-term treatment with amiodarone.

Amiodarone-induced ultrastructural changes in canine myocardial fibers

Chronic clinical toxicity with amiodarone, a unique antiarrhythmic drug, is associated with intracellular myelinoid inclusion bodies in skin, cornea, lung, liver and lymph nodes. The present study was designed to develop a canine animal model to study amiodarone concentration and onset of formation of myelinoid inclusion bodies in the cardiac tissue. Amiodarone was given intravenously in a single dose (40 mg/kg body weight) or multiple doses (40 mg/kg IV + 10 mg/kg IV X 7 days). Amiodarone concentration in the heart was high after a single dose but electron microscopic examination showed a normal ultrastructure. Numerous myelinoid inclusion bodies were found in the myofibrils of the left atria and right and left ventricles after only 7 days of amiodarone treatment. Myelinoid inclusion bodies were identified in several subcellular locations including intercalated disc but most were in close proximity of the mitochondria, sometimes touching and indenting the mitochondrial membrane. The antiarrhythmic effect of the schedule of intravenous amiodarone for 7 days used in this study was minimal, and this correlated with unexpectedly low myocardial levels of the drug and its metabolite. The results are consistent with our previous data of an antiarrhythmic effect with a single intravenous dose of 40 mg/kg body weight associated with high myocardial levels of amiodarone. We conclude that a single large dose of amiodarone with high tissue level may not cause myelinoid inclusion bodies, but they can be readily identified in all heart chambers after only 1 week of amiodarone treatment. This model would be useful to study amiodarone-induced ultrastructural changes in the heart.

Effect of amiodarone on Na+-, K+-ATPase and Mg2+-ATPase activities in rat brain synaptosomes

Amiodarone hydrochloride is a diiodinated antiarrhythmic agent widely used in the treatment of cardiac disorders. With the increasing use of amiodarone, several untoward effects have been recognized and neuropathy following amiodarone therapy has recently been reported. The present studies were carried out to study the effect of amiodarone on rat brain synaptosomal ATPases in an effort to understand its mechanism of action. Na+, K+-ATPase and oligomycin sensitive Mg2+ ATPase activities were inhibited by amiodarone in a concentration dependent manner with IC50 values of 50 microM and 10 microM respectively. [3H]ouabain binding was also decreased in a concentration dependent manner with an IC50 value of 12 microM, and 50 microM amiodarone totally inhibited [3H]ouabain binding. Kinetics of [3H]ouabain binding studies revealed that amiodarone inhibition of [3H]ouabain binding is competitive. K+-activated p-nitrophenyl phosphatase activity showed a maximum inhibition of 32 per cent at 200 microM amiodarone. Synaptosomal ATPase activities did not show any change in rats treated with amiodarone (20 mg kg-1 day-1) for 6 weeks, when compared to controls. The treatment period may be short, since the reported neurological abnormalities in patients were observed during 3-5 years of treatment. The present results suggest that amiodarone induced neuropathy may be due to its interference with sodium dependent phosphorylation of Na+, K+-ATPase reaction, thereby affecting active ion transport phenomenon and oxidative phosphorylation resulting in low turnover of ATP in the nervous system.

Amiodarone: pharmacology and antiarrhythmic and adverse effects

Amiodarone is a benzofuran derivative that has been effective for the treatment of both supraventricular and ventricular tachyarrhythmias. It has a large volume of distribution, moderate bioavailability and a long half-life. Its pharmacokinetics are not well understood and its tissue distribution is not typical of a 2-compartment model. Due to ocular, dermatologic, gastrointestinal, neurologic, cardiovascular, thyroid and pulmonary toxicity, amiodarone should be reserved for use in patients with refractory and/or life-threatening arrhythmias.

Effect of phenobarbitone on the pharmacokinetics and tissue levels of amiodarone in the rat

Phenobarbitone pretreatment has been shown to increase amiodarone total clearance and decrease amiodarone elimination half-life after a single intravenous amiodarone dose in the rat. Coadministration of phenobarbitone with amiodarone for 7 days resulted in decreased tissue amiodarone levels compared to controls. These results may have implications for patients undergoing therapy with amiodarone and concomitant potent enzyme inducing drugs.

Life expectancy analysis in patients with Chagas' disease: prognosis after one decade (1973-1983)

We studied the evolution of chronic Chagas' disease in 107 patients with a positive Guerreiro-Machado reaction and 22 non-chagasic, non-heart disease control subjects for a follow-up period of 3 to 10 years (mean follow-up of 4.9 years). After completion of invasive and non-invasive studies, chagasic patients were classified into four groups: IA (normal ECG, without heart disease; 18 patients); IB (normal ECG, early left ventricular segmental abnormalities; 13 patients); II (abnormal ECG, advanced myocardial damage, no signs of heart failure; 42 patients); and III (abnormal ECG, end-stage, congestive heart failure; 34 patients). One out of five group IA patients re-studied with invasive methods evolved to group IB (20%); 4 group IB patients evolved to group II (33%) and 6 group II patients evolved to group III (15%). The life expectancy of patients in groups IA and IB (normal ECG) was similar to that of our control group, whereas in groups II and III it was significantly decreased (P less than 0.001). Nine group II patients (23%) and 28 group III patients (82%) died during the follow-up period. Main terminal events were refractory congestive heart failure, sudden death and systemic thromboembolism. Our findings suggest that chronic Chagas' disease follows an evolutionary course from asymptomatic, normal ECG group I stage to arrhythmic (II) and congestive (III) stages. Subjects with a positive Guerreiro-Machado reaction showed a significantly lower life expectancy than our control group, but only when clinical and/or ECG abnormalities were identified.