Comparative antiarrhythmic efficacy of verapamil, 17-monochloracetylajmaline, mexiletine and amiodarone in patients with severe chagasic myocarditis: relation with the underlying arrhythmogenic mechanisms

Drug repurposing for parasitic protozoan diseases

Protozoan parasites are major hazards to human health, society, and the economy, especially in equatorial regions of the globe. Parasitic diseases, including leishmaniasis, malaria, and others, contribute towards majority of morbidity and mortality. Around 1.1 million people die from these diseases annually. The lack of licensed vaccinations worsens the worldwide impact of these diseases, highlighting the importance of safe and effective medications for their prevention and treatment. However, the appearance of drug resistance in parasites continuously affects the availability of medications. The demand for novel drugs motivates global antiparasitic drug discovery research, necessitating the implementation of many innovative ways to maintain a continuous supply of promising molecules. Drug repurposing has come out as a compelling tool for drug development, offering a cost-effective and efficient alternative to standard de novo approaches. A thorough examination of drug repositioning candidates revealed that certain drugs may not benefit significantly from their original indications. Still, they may exhibit more pronounced effects in other disorders. Furthermore, certain medications can produce a synergistic effect, resulting in enhanced therapeutic effectiveness when given together. In this chapter, we outline the approaches employed in drug repurposing (sometimes referred to as drug repositioning), propose novel strategies to overcome these hurdles and fully exploit the promise of drug repurposing. We highlight a few major human protozoan diseases and a range of exemplary drugs repurposed for various protozoan infections, providing excellent outcomes for each disease.

Effectiveness and safety of mexiletine in patients at risk for (recurrent) ventricular arrhythmias: a systematic review

While mexiletine has been used for over 40 years for prevention of (recurrent) ventricular arrhythmias and for myotonia, patient access has recently been critically endangered. Here we aim to demonstrate the effectiveness and safety of mexiletine in the treatment of patients with (recurrent) ventricular arrhythmias, emphasizing the absolute necessity of its accessibility. Studies were included in this systematic review (PROSPERO, CRD42020213434) if the efficacy or safety of mexiletine in any dose was evaluated in patients at risk for (recurrent) ventricular arrhythmias with or without comparison with alternative treatments (e.g. placebo). A systematic search was performed in Ovid MEDLINE, Embase, and in the clinical trial registry databases ClinicalTrials.gov and ICTRP. Risk of bias were assessed and tailored to the different study designs. Large heterogeneity in study designs and outcome measures prompted a narrative synthesis approach. In total, 221 studies were included reporting on 8970 patients treated with mexiletine. Age ranged from 0 to 88 years. A decrease in ventricular arrhythmias of >50% was observed in 72% of the studies for pre-mature ventricular complexes, 64% for ventricular tachycardia, and 33% for ventricular fibrillation. Electrocardiographic effects of mexiletine were small; only in a subset of patients with primary arrhythmia syndromes, a relative (desired) QTc decrease was reproducibly observed. As for adverse events, gastrointestinal complaints were most frequently observed (33% of the patients). In this systematic review, we present all the currently available knowledge of mexiletine in patients at risk for (recurrent) ventricular arrhythmias and show that mexiletine is both effective and safe.

Amiodarone for arrhythmia in patients with Chagas disease: A systematic review and individual patient data meta-analysis

Background

Chagas disease is a neglected chronic condition caused by Trypanosoma cruzi, with high prevalence and burden in Latin America. Ventricular arrhythmias are common in patients with Chagas cardiomyopathy, and amiodarone has been widely used for this purpose. The aim of our study was to assess the effect of amiodarone in patients with Chagas cardiomyopathy.

Methodology

We searched MEDLINE, Embase and LILACS up to January 2018. Data from randomized and observational studies evaluating amiodarone use in Chagas cardiomyopathy were included. Two reviewers selected the studies, extracted data and assessed risk of bias. Overall quality of evidence was accessed using Grading of Recommendations Assessment, Development and Evaluation (GRADE).

Principal findings

We included 9 studies (3 before-after studies, 5 case series and 1 randomized controlled trial). Two studies with a total of 38 patients had the full dataset, allowing individual patient data (IPD) analysis. In 24-hour Holter, amiodarone reduced the number of ventricular tachycardia episodes in 99.9% (95%CI 99.8%-100%), ventricular premature beats in 93.1% (95%CI 82%-97.4%) and the incidence of ventricular couplets in 79% (RR 0.21, 95%CI 0.11–0.39). Studies not included in the IPD analysis showed a reduction of ventricular premature beats (5 studies), ventricular tachycardia (6 studies) and ventricular couplets (1 study). We pooled the incidence of adverse side effects with random effects meta-analysis; amiodarone was associated with corneal microdeposits (61.1%, 95%CI 19.0–91.3, 5 studies), gastrointestinal events (16.1%, 95%CI 6.61–34.2, 3 studies), sinus bradycardia (12.7%, 95%CI 3.71–35.5, 6 studies), dermatological events (10.6%, 95%CI 4.77–21.9, 3 studies) and drug discontinuation (7.68%, 95%CI 4.17–13.7, 5 studies). Quality of evidence ranged from moderate to very low.

Conclusions

Amiodarone is effective in reducing ventricular arrhythmias, but there is no evidence for hard endpoints (sudden death, hospitalization). Although our findings support the use of amiodarone, it is important to balance the potential benefits and harms at the individual level for decision-making.

Chagas disease is a chronic neglected tropical disease, with high prevalence and burden in Latin America. About 30% of chronically infected patients develop Chagas cardiomyopathy. Ventricular arrhythmias are common in patients with Chagas cardiomyopathy and treatment approaches include medications, resynchronization therapy, and implantable cardioverter defibrillator. Studies published from 1980 to 1990 have evaluated the effect of amiodarone. According to our systematic review and individual patient meta-analysis, amiodarone reduced ventricular tachycardia, ventricular premature beats and incidence of ventricular couplets. Although the strong evidence of clinical benefit with arrhythmia reduction, this information should be interpreted with caution, since arrhythmia is a surrogate outcome and since its clinical impact on death and hospitalization reduction over time is not clear. Little information was identified related to hard endpoints. Regarding side effects, our systematic review observed that amiodarone was associated with corneal microdeposits, gastrointestinal events, sinus bradycardia, dermatological events, pneumonitis, hypothyroidism and drug discontinuation. The currently available evidence shows that amiodarone seems to be an effective antiarrhythmic drug for patients with Chagas disease, especially in settings where an implantable cardioverter defibrillator is not available or affordable, but that a balance between potential benefits and harms at the individual level is needed.

Treatment of Chagas cardiomyopathy

Chagas' disease (ChD), caused by the protozoa Trypanosoma cruzi (T. cruzi), was discovered and described by the Brazilian physician Carlos Chagas in 1909. After a century of original description, trypanosomiasis still brings much misery to humanity and is classified as a neglected tropical disease prevalent in underdeveloped countries, particularly in South America. It is an increasing worldwide problem due to the number of cases in endemic areas and the migration of infected subjects to more developed regions, mainly North America and Europe. Despite its importance, chronic chagas cardiomyopathy (CCC) pathophysiology is yet poorly understood, and independently of its social, clinical, and epidemiological importance, the therapeutic approach of CCC is still transposed from the knowledge acquired from other cardiomyopathies. Therefore, the objective of this review is to describe the treatment of Chagas cardiomyopathy with emphasis on its peculiarities.

The emerging role of amiodarone and dronedarone in Chagas disease

Chagas disease has emerged as an important health problem in the Americas and, with globalization, in other parts of the world. Drug therapy for this parasitic infection has remained largely ineffective, especially in chronic stages of the disease. However, developments in experimental therapy might signal an important advance for the management of patients with Chagas disease. Herein, we review studies on the potential use of the benzofuran derivatives amiodarone and dronedarone in patients with Chagas disease. These agents have a dual role, not only as primary antiarrhythmic drugs, but also as antiparasitic agents. We believe that this 'kill two birds with one stone' approach represents a new tactic for the treatment of Chagas disease using currently approved drugs.

Current and emerging therapeutic options for the treatment of chronic chagasic cardiomyopathy

Chagas’ disease is an endemic disease in Latin America caused by a unicellular parasite (Trypanosoma cruzi) that affects almost 18 million people. This condition involves the heart, causing heart failure, arrhythmias, heart block, thromboembolism, stroke, and sudden death. In this article, we review the current and emerging treatment of Chagas’ cardiomyopathy focusing mostly on management of heart failure and arrhythmias. Heart failure therapeutical options including drugs, stem cells and heart transplantation are revised. Antiarrhythmic drugs, catheter ablation, and intracardiac devices are discussed as well. Finally, the evidence for a potential role of specific antiparasitic treatment for the prevention of cardiovascular disease is reviewed.

Stereoselective metabolism of mexiletine in Chagasic women with ventricular arrhythmias

Following a week of racemic mexiletine HCl at 200 mg tid (2x100 mg capsules), stereoselective aliphatic hydroxylation was studied in eight Chagasic women with chronic ventricular arrhythmias (52-67 yrs) with no history of renal or hepatic diseases. Blood samples were collected at dose interval up to 24 h of drug administration. Plasma concentrations of R(-) and S(+) mexiletine (MEX) and its metabolite hydroxymethylmexiletine (HMM) were determined by HPLC after derivatization with chiral reagent. The differences between R(-) and S(+) enantiomers were compared by paired t-test. Results are mean (95% CI). The following differences (p < 0.05) between R(-) and S(+) enantiomers, respectively, were found: MEX AUCss(0-8) 2.34 (1.84-2.85) vs 2.55 (1.97-3.13) microg.ml(-1) x h(-1); MEX CL/f 11.27 (7.77-14.77) vs 10.46 (7.18-13.74)ml.min(-1).Kg(-1); HMM Cmax 38.26 (24.3-52.22) vs 16.73 (10.1-23.29)ng.ml(-1); HMM Tmax 4.71 (2.67-6.76) vs 3.29 (1.24-5.33) h and HMM AUCss(0-8) 253.50 (165.39-341.61) vs 103.70 (69.51-137.90)ng.ml(-1).h(-1). The AUCss(0-8) ratio R(-)/S(+) for MEX was 0.93 (0.87-0.98) while for HMM was 2.50 (2.16-2.85). Distribution of MEX and HMM enantiomers were not significantly different. In this study we demonstrate that kinetic disposition of mexiletine exhibits stereoselectivity in vivo and that aliphatic hydroxylation is favored for R(-) mexiletine in Chagasic women with ventricular arrhythmias.

Cardiac arrhythmias in Chagas' heart disease

Chagas' disease is a chronic parasitosis affecting most Latin American countries. Its most important clinical manifestation is a late developing chronic myocarditis and, much less frequently, an early acute myocarditis. Chagasic myocardial damage is microfocal and disseminated throughout the heart. In most cases, the coexistence of areas of myocytic degeneration, inflammatory infiltration, and fibrosis suggests a permanent evolving process. Commonly, chronic chagasic myocarditis resembles a dilated cardiomyopathy, with characteristic ECG abnormalities (atrial and ventricular extrasystoles, intraventricular and/or AV conduction disturbances, and primary ST-T wave changes). Since myocardial damage is scattered throughout the heart, the ECG abnormalities (arrhythmias, conduction disturbances, and repolarization changes) are also representative of the widespread cardiac involvement. Thus, sick sinus syndrome, atrial extrasystoles, intraatrial conduction disturbances, and atrial fibrillation or flutter are common findings in different stages of the disease. At the ventricular level, both conduction disturbances and arrhythmias are conspicuous expressions of the myocardial damage. Right bundle branch block alone or in combination with left anterior hemiblock are the most common conduction defects. Further compromise of the conduction system can lead to different degrees of AV block. Chagas' disease is the main cause of bundle branch block and AV block in endemic areas. In advanced cases of Chagas' heart disease, ventricular premature contractions are extremely frequent, multiform, and repetitive (couplets and runs of ventricular tachycardia), and show R on T phenomenon. These arrhythmias are usually aggravated by increased sympathetic tone, implying an enhanced risk of cardiac sudden death among chagasic patients, which is sometimes the first manifestation of the illness. Chronic chagasic myocarditis is the leading cause of cardiovascular death, mostly as a consequence of heart failure and sudden death, in areas where the disease is endemic.

Effects of phenytoin on the ventricular tachyarrhythmias of chronic Chagas' disease

The effects of phenytoin on the ventricular tachyarrhythmias of 11 patients with chronic chagasic myocarditis were investigated, and correlated with the serum phenytoin levels. Physical examination, laboratory tests and 24- to 48-h ambulatory electrocardiographic recordings were performed before, during (7-14 days) and after treatment with phenytoin (4-6 mg/kg/day, orally, in three divided doses). Significant (greater than 90%) reduction of couplets, bigeminy and runs of ventricular tachycardia were observed in 50-67% of the patients, whereas the frequency of isolated premature ventricular contractions was significantly (greater than 70%) reduced in only 2 patients (18%). Proarrhythmic activity was not observed and adverse side effects were of mild intensity and usually transient, except in one patient, who developed pruritus and skin rash in the presence of toxic phenytoin serum levels (27 micrograms/ml). It is suggested that phenytoin may be useful for the control of repetitive forms of ventricular tachyarrhythmias in selected patients with chronic chagasic myocarditis.

Mexiletine. A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic use in the treatment of arrhythmias

As a member of the class Ib antiarrhythmic drugs mexiletine's primary mechanism of action is blocking fast sodium channels, reducing the phase 0 maximal upstroke velocity of the action potential. It increases the ratio of effective refractory period to action potential duration, but has little effect on conductivity. Unlike quinidine it does not prolong QRS and QT (QTc) intervals. In the dosage range 600 to 900 mg daily mexiletine effectively suppresses premature ventricular contractions (PVCs) in 25% to 79% of patients, with or without underlying cardiac disease. In comparative studies the response rate was comparable to that with quinidine or disopyramide. However, the use of antiarrhythmic therapy in patients with asymptomatic arrhythmias is controversial. More importantly, mexiletine abolishes spontaneous or inducible ventricular tachycardia or fibrillation in the short term in 20% to 50% of patients with refractory arrhythmias. Arrhythmia suppression is maintained in 57% to over 80% of these early therapeutic successes in the long term, with mexiletine alone or in combination with another antiarrhythmic drug. As with other antiarrhythmic drugs, there is no substantial evidence that administration of mexiletine after acute myocardial infarction improves long term prognosis. Although the incidence of adverse effects associated with mexiletine is high, the majority are minor gastrointestinal or neurological effects which can be adequately controlled through dosage adjustment. Furthermore, mexiletine has minimal effects on haemodynamic variables, or on cardiac function in patients with or without pre-existing deterioration of left ventricular function, and it appears to have a low proarrhythmic potential. Thus, while the therapeutic efficacy of mexiletine for the prevention or suppression of symptomatic ventricular arrhythmias may be no greater than that of other antiarrhythmic drugs, and less than that of some (e.g. amiodarone), it is effective in a significant proportion of patients refractory to other treatments and can be administered without causing adverse haemodynamic effects to patients with complicating factors such as acute myocardial infarction or congestive heart failure.

A comparison of antiarrhythmic drugs for the suppression of ventricular ectopic depolarizations: a meta-analysis

This article reports the results of a meta-analysis of the effectiveness of antiarrhythmic drugs for the suppression of ventricular ectopic depolarizations. We analyzed 97 published articles that referred to a total of 27 drugs and contained data from 2989 patient-treatment trials; our goal was to determine the number of patients responding to therapy, defined as greater than or equal to 80% suppression of ventricular ectopic depolarizations. By means of logistic regression we tested the effect of 10 clinical and experimental variables on the likelihood of response to therapy. The likelihood of a drug response was significantly affected by the following six variables: increased by the use of dose titration (t = 3.59, p less than 0.0001), increased by the use of a higher daily dose (t = 3.21, p less than 0.0001), decreased by older age (t-2.67, p = 0.004), decreased by the use of blinding (t = -2.28, p = 0.011), increased by treating more male patients (t = 1.72, p = 0.043), and decreased by the presence of cardiovascular disease (t = -1.52, p = 0.064). Incorporating these six variables into our logistic regression model, we adjusted the response rate in each published study and calculated the mean response and standard error for each drug. Of the drugs tested in at least 100 patients, the most effective were amiodarone (estimated response rate 90%), encainide (80%), flecainide (79%), and propafenone (74%). Class IC drugs were significantly more effective than class IB and II drugs (p less than 0.05). With the exception of lorcainide and moricizine, class IC drugs were also more effective than class IA drugs (p less than 0.05). Amiodarone was significantly more effective than all drugs except encainide and flecainide (p less than 0.05). We found no significant differences among the response rates to class IA, IB, and II drugs. Whereas several patient and study characteristics affect the likelihood of response to antiarrhythmic drugs, class IC drugs and amiodarone are significantly more effective than other drugs in suppressing ventricular ectopic depolarizations.

Amiodarone in the management of cardiac arrhythmias: current concepts

This article reviews current information on the clinical pharmacology, therapeutic utility, and adverse reactions of amiodarone, with emphasis on guidelines for its rational use.