Low dose quinidine-mexiletine combination therapy versus quinidine monotherapy for treatment of ventricular arrhythmias

Perspective on Antiarrhythmic Drug Combinations

Physicians use multiple drugs in combination to treat hypertension, heart failure, diabetes mellitus, angina, hyperlipidemia, and many other cardiovascular conditions and risk factors. However, administering antiarrhythmic drugs (AAD) in combination is rarely discussed. Yet, the possibility of increasing efficacy and/or tolerance and/or safety of AADs (by adding mechanisms, offsetting adverse mechanisms, and/or using lower doses) exists. Unfortunately, this topic has not been reviewed in any contemporary cardiac literature of which we are aware, although information regarding AAD combinations has been published. In conclusion, and accordingly, this review discusses the possibility of using AAD combinations for both ventricular arrhythmias and atrial fibrillation, in which the rationale for such combinations, considerations for such combinations, and supporting literature are covered.

Quinidine in the Management of Recurrent Ventricular Arrhythmias: A Reappraisal

OBJECTIVE

This study aimed to review the utility of quinidine in patients presenting with recurrent sustained ventricular arrhythmia (VA) and limited antiarrhythmic drug (AAD) options.

BACKGROUND

Therapeutic options are often limited in patients with structural heart disease and recurrent VAs. Quinidine has an established role in rare arrhythmic syndromes, but its potential use in other difficult VAs has not been assessed in the present era.

METHODS

We performed a retrospective analysis of 37 patients who had in-hospital quinidine initiation after multiple other therapies failed for VA suppression at our tertiary referral center. Clinical data and outcomes were obtained from the medical record.

RESULTS

Of 30 patients with in-hospital quantifiable VA episodes, quinidine reduced acute VA from a median of 3 episodes (interquartile range [IQR]: 2 to 7.5) to 0 (IQR: 0 to 0.5) during medians of 3 days before and 4 days after quinidine initiation (p < 0.001). VA events decreased from a median of 10.5 episodes per day (IQR: 5 to 15) to 0.5 episodes (IQR: 0 to 4) after quinidine initiation in the 12 patients presenting with electrical storm (p = 0.004). Among the 24 patients discharged on quinidine, 13 (54.2%) had VA recurrence during a median of 138 days. Adverse effects in 9 of the 37 patients (24.3%) led to drug discontinuation, most commonly gastrointestinal intolerance.

CONCLUSIONS

In patients with recurrent VAs and structural heart disease who have limited treatment options, quinidine can be useful, particularly as a short-term therapy.

Assessment of Multi-Ion Channel Block in a Phase I Randomized Study Design: Results of the CiPA Phase I ECG Biomarker Validation Study

Balanced multi‐ion channel‐blocking drugs have low torsade risk because they block inward currents. The Comprehensive In Vitro Proarrhythmia Assay (CiPA) initiative proposes to use an in silico cardiomyocyte model to determine the presence of balanced block, and absence of heart rate corrected J‐T_peak (J‐T_peakc) prolongation would be expected for balanced blockers. This study included three balanced blockers in a 10‐subject‐per‐drug parallel design; lopinavir/ritonavir and verapamil met the primary end point of ΔΔJ‐T_peakc upper bound < 10 ms, whereas ranolazine did not (upper bounds of 8.8, 6.1, and 12.0 ms, respectively). Chloroquine, a predominant blocker of the potassium channel encoded by the ether‐à‐go‐go related gene (hERG), prolonged ΔΔQTc and ΔΔJ‐T_peakc by ≥ 10 ms. In a separate crossover design, diltiazem (calcium block) did not shorten dofetilide‐induced ΔQTc prolongation, but shortened ΔJ‐T_peakc and prolonged ΔT_peak‐T_end. Absence of J‐T_peakc prolongation seems consistent with balanced block; however, small sample size (10 subjects) may be insufficient to characterize concentration‐response in some cases.

Adult Human Primary Cardiomyocyte-Based Model for the Simultaneous Prediction of Drug-Induced Inotropic and Pro-arrhythmia Risk

Cardiac safety remains the leading cause of drug development discontinuation. We developed a human cardiomyocyte-based model that has the potential to provide a predictive preclinical approach for simultaneously predicting drug-induced inotropic and pro-arrhythmia risk.

Methods: Adult human primary cardiomyocytes from ethically consented organ donors were used to measure contractility transients. We used measures of changes in contractility parameters as markers to infer both drug-induced inotropic effect (sarcomere shortening) and pro-arrhythmia (aftercontraction, AC); contractility escape (CE); time to 90% relaxation (TR90). We addressed the clinical relevance of this approach by evaluating the effects of 23 torsadogenic and 10 non-torsadogenic drugs. Each drug was tested separately at four multiples of the free effective therapeutic plasma concentration (fETPC).

Results: Human cardiomyocyte-based model differentiated between torsadogenic and non-torsadogenic drugs. For example, dofetilide, a torsadogenic drug, caused ACs and increased TR90 starting at 10-fold the fETPC, while CE events were observed at the highest multiple of fETPC (100-fold). Verapamil, a non-torsadogenic drug, did not change TR90 and induced no AC or CE up to the highest multiple of fETPCs tested in this study (222-fold). When drug pro-arrhythmic activity was evaluated at 10-fold of the fETPC, AC parameter had excellent assay sensitivity and specificity values of 96 and 100%, respectively. This high predictivity supports the translational safety potential of this preparation and of the selected marker. The data demonstrate that human cardiomyocytes could also identify drugs associated with inotropic effects. hERG channel blockers, like dofetilide, had no effects on sarcomere shortening, while multi-ion channel blockers, like verapamil, inhibited sarcomere shortening.

Conclusions: Isolated adult human primary cardiomyocytes can simultaneously predict risks associated with inotropic activity and pro-arrhythmia and may enable the generation of reliable and predictive data for assessing human cardiotoxicity at an early stage in drug discovery.

Mechanistic Model-Informed Proarrhythmic Risk Assessment of Drugs: Review of the "CiPA" Initiative and Design of a Prospective Clinical Validation Study

The Comprehensive in vitro Proarrhythmia Assay (CiPA) initiative is developing and validating a mechanistic‐based assessment of the proarrhythmic risk of drugs. CiPA proposes to assess a drug's effect on multiple ion channels and integrate the effects in a computer model of the human cardiomyocyte to predict proarrhythmic risk. Unanticipated or missed effects will be assessed with human stem cell‐derived cardiomyocytes and electrocardiogram (ECG) analysis in early phase I clinical trials. This article provides an overview of CiPA and the rationale and design of the CiPA phase I ECG validation clinical trial, which involves assessing an additional ECG biomarker (J‐Tpeak) for QT prolonging drugs. If successful, CiPA will 1) create a pathway for drugs with hERG block / QT prolongation to advance without intensive ECG monitoring in phase III trials if they have low proarrhythmic risk; and 2) enable updating drug labels to be more informative about proarrhythmic risk, not just QT prolongation.

Late sodium current block for drug-induced long QT syndrome: Results from a prospective clinical trial

Drug-induced long QT syndrome has resulted in many drugs being withdrawn from the market. At the same time, the current regulatory paradigm for screening new drugs causing long QT syndrome is preventing drugs from reaching the market, sometimes inappropriately. In this study, we report the results of a first-of-a-kind clinical trial studying late sodium (mexiletine and lidocaine) and calcium (diltiazem) current blocking drugs to counteract the effects of hERG potassium channel blocking drugs (dofetilide and moxifloxacin). We demonstrate that both mexiletine and lidocaine substantially reduce heart-rate corrected QT (QTc) prolongation from dofetilide by 20 ms. Furthermore, all QTc shortening occurs in the heart-rate corrected J-Tpeak (J-Tpeak c) interval, the biomarker we identified as a sign of late sodium current block. This clinical trial demonstrates that late sodium blocking drugs can substantially reduce QTc prolongation from hERG potassium channel block and assessment of J-Tpeak c may add value beyond only assessing QTc.

Antiarrhythmic agents: drug interactions of clinical significance

The management of cardiac arrhythmias has grown more complex in recent years. Despite the recent focus on nonpharmacological therapy, most clinical arrhythmias are treated with existing antiarrhythmics. Because of the narrow therapeutic index of antiarrhythmic agents, potential drug interactions with other medications are of major clinical importance. As most antiarrhythmics are metabolised via the cytochrome P450 enzyme system, pharmacokinetic interactions constitute the majority of clinically significant interactions seen with these agents. Antiarrhythmics may be substrates, inducers or inhibitors of cytochrome P450 enzymes, and many of these metabolic interactions have been characterised. However, many potential interactions have not, and knowledge of how antiarrhythmic agents are metabolised by the cytochrome P450 enzyme system may allow clinicians to predict potential interactions. Drug interactions with Vaughn-Williams Class II (beta-blockers) and Class IV (calcium antagonists) agents have previously been reviewed and are not discussed here. Class I agents, which primarily block fast sodium channels and slow conduction velocity, include quinidine, procainamide, disopyramide, lidocaine (lignocaine), mexiletine, flecainide and propafenone. All of these agents except procainamide are metabolised via the cytochrome P450 system and are involved in a number of drug-drug interactions, including over 20 different interactions with quinidine. Quinidine has been observed to inhibit the metabolism of digoxin, tricyclic antidepressants and codeine. Furthermore, cimetidine, azole antifungals and calcium antagonists can significantly inhibit the metabolism of quinidine. Procainamide is excreted via active tubular secretion, which may be inhibited by cimetidine and trimethoprim. Other Class I agents may affect the disposition of warfarin, theophylline and tricyclic antidepressants. Many of these interactions can significantly affect efficacy and/or toxicity. Of the Class III antiarrhythmics, amiodarone is involved in a significant number of interactions since it is a potent inhibitor of several cytochrome P450 enzymes. It can significantly impair the metabolism of digoxin, theophylline and warfarin. Dosages of digoxin and warfarin should empirically be decreased by one-half when amiodarone therapy is added. In addition to pharmacokinetic interactions, many reports describe the use of antiarrhythmic drug combinations for the treatment of arrhythmias. By combining antiarrhythmic drugs and utilising additive electrophysiological/pharmacodynamic effects, antiarrhythmic efficacy may be improved and toxicity reduced. As medication regimens grow more complex with the aging population, knowledge of existing and potential drug-drug interactions becomes vital for clinicians to optimise drug therapy for every patient.

Electrophysiologic effects and predictors of success of combination therapy with class Ia and Ib antiarrhythmic drugs for sustained ventricular arrhythmias

Antiarrhythmic drugs remain the first line of therapy in patients with sustained ventricular arrhythmias. Although success with class Ia antiarrhythmic medications has been limited, there is evidence that the addition of a class Ib agent may improve results. A total of 110 consecutive patients referred for electrophysiologic evaluation who had inducible sustained ventricular arrhythmias resistant to a class Ia agent underwent repeat electrophysiologic study after the addition of a class Ib drug. Patients with ejection fraction >40% and ventricular fibrillation inducible in the baseline study had an 80% response rate, whereas those with inducible ventricular tachycardia and ejection fraction < or = 40% responded 11% of the time. Responders demonstrated marked prolongation of ventricular refractoriness and slight shortening of the QRS, whereas nonresponders had QRS prolongation and a more modest increase in ventricular refractoriness. Thus, the efficacy of class Ia/Ib combination therapy in patients with inducible sustained ventricular arrhythmias refractory to a class Ia drugs alone can be predicted by baseline variables. Marked prolongation of ventricular refractoriness in the absence of QRS prolongation appears to be a key factor in the success of this combination.

Effect of the combination of low-dose mexiletine and metoprolol on ventricular arrhythmia

Antiarrhythmic drug therapy is often ineffective or poorly tolerated. Combining antiarrhythmic agents with different electrophysiologic properties may have a synergistic antiarrhythmic effect when compared with each drug alone. If a lower dose of each drug can be used, combination therapy may also result in lower incidence of side effects. The goal of our study was to assess the complementary effect of low-dose mexiletine and metoprolol, when compared with either drug alone. Ten patients with frequent ventricular arrhythmias including 7 patients with nonsustained ventricular tachycardia were evaluated in an open-label sequential study. The response to drug therapy was evaluated by 24-h continuous EKG monitoring, exercise stress testing, and echocardiogram after each treatment. Combination therapy effectively reduced ventricular arrhythmias in 8 patients (80%) in contrast to only 1 patient (10%) on metoprolol alone and 4 patients (40%) on mexiletine alone. In 5 patients (71%) ventricular tachycardia was abolished. The number of couplets was reduced from 51 +/- 39 to 1.9 +/- 2.4 (p less than 0.01) and total premature ventricular beats from 7790 +/- 9047 to 597 +/- 515 (p = 0.06). Combination therapy was well tolerated without proarrhythmia or precipitation of congestive heart failure. It is concluded that low-dose mexiletine combined with metoprolol is effective in suppressing ventricular arrhythmias in selected patients, and enhances the antiarrhythmic effect of either drug alone without significant side effects.

Time course of moricizine's effect on signal-averaged and 12 lead electrocardiograms: insights into mechanism of action

The mechanism of action of moricizine, a new antiarrhythmic agent used in the Cardiac Arrhythmia Suppression Trial, is incompletely characterized. In addition, because moricizine is extensively metabolized, plasma moricizine concentration has an unknown relation to myocardial drug effect. Signal-averaged and standard electrocardiograms (ECGs) were used to monitor moricizine's myocardial effects in 16 patients with frequent ventricular premature complexes taking 600 to 900 mg daily. Three signal-averaged ECG variables were measured: total filtered QRS duration (fQRS), root-mean-square voltage in the terminal 40 ms of the QRS complex (V40) and the terminal low amplitude duration less than 40 microV (LAS). At steady state, plasma samples were collected and serial recordings of signal-averaged and standard ECGs were taken at 0, 1, 2, 4, 6 and 8 h after moricizine administration. A 24 h ambulatory ECG was recorded throughout the test period. Moricizine prolonged the fQRS (p less than 0.05) and decreased the V40 (p less than 0.05) of the signal-averaged ECG and prolonged the QRS (p less than 0.05) and corrected JT (JTc) intervals (p less than 0.05) of the standard ECG. The time course of the signal-averaged and standard ECG variables paralleled plasma moricizine concentration; that is, the maximal changes occurred at 1 to 2 h and declined to time 0 values at 8 h. The maximal changes were: fQRS (+8%), V40 (-33%), QRS (+8%) and JTc (+4%). Thus, dynamic changes were observed for intraventricular conduction (fQRS, QRS) and ventricular repolarization (JTc) over the dosing interval.(ABSTRACT TRUNCATED AT 250 WORDS)

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.