Mexiletine for ventricular arrhythmias

Relevance of mexiletine in the era of evolving antiarrhythmic therapy of ventricular arrhythmias

Despite impressive developments in the field of ventricular arrhythmias, there is still a relevant number of patients with ventricular arrhythmias who require antiarrhythmic drug therapy and may, e.g., in otherwise drug and/or ablation refractory situations, benefit from agents known for decades, such as mexiletine. Through its capability of blocking fast sodium channels in cardiomyocytes, it has played a minor to moderate antiarrhythmic role throughout the recent decades. Nevertheless, certain patients with structural heart disease suffering from drug-refractory, i.e., mainly amiodarone refractory ventricular arrhythmias, as well as those with selected forms of congenital long QT syndrome (LQTS) may nowadays still benefit from mexiletine. Here, we outline mexiletine's cellular and clinical electrophysiological properties. In addition, the application of mexiletine may be accompanied by various potential side effects, e.g., nausea and tremor, and is limited by several drug-drug interactions. Thus, we shed light on the current therapeutic role of mexiletine for therapy of ventricular arrhythmias and discuss clinically relevant aspects of its indications based on current evidence.

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.

The effect of methocarbamol and mexiletine on murine muscle spindle function

INTRODUCTION/AIMS

The muscle relaxant methocarbamol and the antimyotonic drug mexiletine are widely used for the treatment of muscle spasms, myotonia, and pain syndromes. To determine whether these drugs affect muscle spindle function, we studied their effect on the resting discharge and on stretch-induced action potential frequencies of proprioceptive afferent neurons.

METHODS

Single unit action potential frequencies of proprioceptive afferents from muscle spindles in the murine extensor digitorum longus muscle of adult C57BL/6J mice were recorded under resting conditions and during ramp-and-hold stretches. Maximal tetanic force of the same muscle after direct stimulation was determined. High-resolution confocal microscopy analysis was performed to determine the distribution of Na_v 1.4 channels, a potential target for both drugs.

RESULTS

Methocarbamol and mexiletine inhibited the muscle spindle resting discharge in a dose-dependent manner with IC₅₀ values around 300 μM and 6 μM, respectively. With increasing concentrations of both drugs, the response to stretch was also affected, with the static sensitivity first followed by the dynamic sensitivity. At high concentrations, both drugs completely blocked muscle spindle afferent output. Both drugs also reversibly reduced the specific force of the extensor digitorum longus muscle after tetanic stimulation. Finally, we present evidence for the presence and specific localization of the voltage-gated sodium channel Na_v 1.4 in intrafusal fibers.

DISCUSSION

In this study we demonstrate that both muscle relaxants affect muscle spindle function, suggesting impaired proprioception as a potential side effect of both drugs. Moreover, our results provide additional evidence of a peripheral activity of methocarbamol and mexiletine.

Pharmacologic Management for Ventricular Arrhythmias: Overview of Anti-Arrhythmic Drugs

Ventricular arrhythmias (Vas) are a life-threatening condition and preventable cause of sudden cardiac death (SCD). With the increased utilization of implantable cardiac defibrillators (ICD), the focus of VA management has shifted toward reduction of morbidity from VAs and ICD therapies. Anti-arrhythmic drugs (AADs) can be an important adjunct therapy in the treatment of recurrent VAs. In the treatment of VAs secondary to structural heart disease, amiodarone remains the most well studied and current guideline-directed pharmacologic therapy. Beta blockers also serve as an important adjunct and are a largely underutilized medication with strong evidentiary support. In patients with defined syndromes in structurally normal hearts, AADs can offer tailored therapies in prevention of SCD and improvement in quality of life. Further clinical trials are warranted to investigate the role of newer therapeutic options and for the direct comparison of established AADs.

Voltage-Gated Sodium Channel Blockers: Synthesis of Mexiletine Analogues and Homologues

Mexiletine is an antiarrhythmic drug belonging to IB class, acting as sodium channel blocker. Besides its well-known activity on arrhythmias, its usefulness in the treatment of myotonia, myotonic dystrophy and amyotrophic lateral sclerosis is now widely recognized. Nevertheless, it has been retired from the market in several countries because of its undesired effects. Thus, several papers were reported in the last years about analogues and homologues of mexiletine being endowed with a wider therapeutic ratio and a more selectivity of action. Some of them showed sodium channel blocking activity higher than the parent compound. It is noteworthy that mexiletine is used in therapy as a racemate even though a difference in the activities of the two enantiomers was widely demonstrated, with (-)-(R)-enantiomer being more active: this finding led several research groups to study mexiletine and its analogues and homologues in their optically active forms. This review summarizes the different synthetic routes used to obtain these compounds. They could represent an interesting starting point to new mexiletine-like compounds without common side effects related to the use of mexiletine.

Anti-arrhythmic therapy in patients with non-ischemic cardiomyopathy

Implantable cardiac defibrillators (ICD) are the foundation of therapy for the prevention of sudden cardiac death. While ICDs prevent SCD, they do not prevent the occurrence of ventricular arrhythmias which are usually symptomatic. Though catheter ablation has been successful in substrate modification of ventricular tachycardia in patients with ischemic cardiomyopathy, there is much less evidence to support its use in non-ischemic cardiomyopathy. Therefore, anti-arrhythmic drugs (AADs) are an essential adjunctive therapy for secondary prevention of ventricular arrhythmias in patients with non-ischemic cardiomyopathy. In patients with hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM), the prevalence of ventricular arrhythmias correlates with the volume of scar as characterized by late gadolinium enhancement. Beta-blockers forms the cornerstone of treatment to prevent ventricular arrhythmias in both HCM and DCM. Disopyramide is an important therapeutic option in HCM as it provides both negative inotropy which reduces obstruction as well as lass I anti-arrhythmic action. In DCM sotalol, through is combined beta-blocking and class III AD effects, significantly reduces the burden of ventricular arrhythmias. Though amiodarone is efficacious in the prevention of ventricular arrhythmias in both HCM and DCM, its use is limited by its side-effects profile. Evidence for AAD therapy for arrhythmogenic right ventricular dysplasia (ARVD) is limited by its low prevalence and lack of studies. ICDs have been shown to reduce SCD regardless of whether patients are receiving AAD therapy.

Advances in the Management of Tachyarrhythmias

Recent developments of both diagnostic and therapeu tic techniques in the management of tachyarrhythmias have broadened the options available to physicians car ing for patients with tachyarrhythmias. Newer diag nostic methods allow more precise identification of the arrhythmia and better understanding of its mechanism. Long-term epidemiologic studies have identified groups of patients who do and do not require antiarrhythmic therapy. Antitachycardia pacemakers and automatic im plantable defibrillators allow effective treatment for pa tients for whom drugs were ineffective or in whom in tolerable side effects developed. Finally, several new antiarrhythmic agents have become available recently. Proper use of these new techniques and drugs requires greater understanding of the pathophysiology of cardiac arrhythmias.

Therapeutic drug monitoring of antiarrhythmic drugs

Most antiarrhythmic drugs fulfil the formal requirements for rational use of therapeutic drug monitoring, as they show highly variable plasma concentration profiles at a given dose and a direct concentration-effect relationship. Therapeutic ranges for antiarrhythmic drugs are, however, often very poorly defined. Effective drug concentrations are based on small studies or studies not designed to establish a therapeutic range, with varying dosage regimens and unstandardised sampling procedures. There are large numbers of nonresponders and considerable overlap between therapeutic and toxic concentrations. Furthermore, no study has ever shown that therapeutic drug monitoring makes a significant difference in clinical outcome. Therapeutic concentration ranges for antiarrhythmic drugs as they exist today can give an overall impression about the drug concentrations required in the majority of patients. They may also be helpful for dosage adjustment in patients with renal or hepatic failure or in patients with possible toxicological or compliance problems. Their use in optimising individual antiarrhythmic therapy, however, is very limited.

Mexiletine's antifibrillatory actions are limited by the occurrence of convulsions in conscious animals

The antiarrhythmic actions of the racemate and enantiomers of mexiletine were studied in conscious and anaesthetised rats. Racemate or enantiomers, at 20 mg/kg i.v., had little effect on ischaemia-induced ventricular fibrillation in conscious or anaesthetised rats. In conscious rats 20 mg/kg caused convulsions in 78-89% of rats when the plasma concentration of racemate was 20 +/- 2 microM. In anaesthetized animals a higher dose (40 mg/kg) of racemate could be given; this completely prevented ischaemia-induced fibrillation when the plasma concentration was 26 +/- 2 microM. Racemate and enantiomers accumulated in the heart and brain of conscious animals to give tissue: plasma ratios of 7.5 and 23, respectively. With electrical stimulation, both racemate and enantiomers dose dependently (4-32 mg/kg) increased threshold currents for induction of ventricular fibrillation, increased refractory period and minimally changed the ECG; findings expected with a Class Ib antiarrhythmic. The above studies failed to show major differences between racemate or enantiomers except for consistently lower (20-30%) plasma concentrations of R(-) at all dose levels. In conclusion, mexiletine prevented ischaemia-induced ventricular fibrillation in anaesthetised animals but only when given at doses producing convulsions in conscious animals.

Fluorimetric determination of mexiletine in serum by high-performance liquid chromatography using pre-column derivatization with fluorescamine

A simple, specific and sensitive micro-scale method for the assay of the antiarrhythmic agent mexiletine in human serum is described. The method uses high-performance liquid chromatography, with pre-column fluorimetric derivatization by fluorescamine. Following extraction with diethyl ether, mexiletine and 4-methylmexiletine (an internal standard) were derivatized with fluorescamine under weakly alkaline condition (pH 9.0) and chromatographed on a reversed-phase column with aqueous methanol-2-propanol as the mobile phase. The two fluorescent derivatives of mexiletine and the internal standard were separated as clear single peaks, and no interfering peaks were observed on the chromatograms. The detection limit for mexiletine was 0.005 micrograms/ml from only 100 microliters of serum, and the calibration curves in the range 0.01-5 micrograms/ml were linear, with an overall coefficient of variation of less than 5%. The analytical recovery of a known amount of mexiletine added to serum was almost 100%. This method proved to be effective in the rapid monitoring of the serum concentrations in patients who received this potent antiarrhythmic drug.

Mexiletine versus quinidine as first-line antiarrhythmia therapy: results from consecutive trials

The efficacy of mexiletine and quinidine in controlling ventricular couplets (VC) and ventricular tachycardia (VT) was compared in 156 trials (78 for each drug) in 114 consecutive patients. Forty-two patients received both drugs, whereas 36 patients were given mexiletine, and 36 patients received quinidine only. During acute drug testing, mexiletine was more effective than quinidine in controlling VC and VT (54 vs. 32 patients, respectively, P less than .001) and resulted in fewer proarrhythmic events (4 vs. 13, respectively, P less than .05). Mean duration of follow-up for mexiletine (27 +/- 14 mo) and quinidine (21 +/- 14 mo) did not differ. Long-term success was more frequent with mexiletine administration than quinidine administration (33/47 vs. 10/30 patients, respectively, P less than .01). The incidence of sudden death during follow-up with the two drugs did not differ overall, but more patients with ejection fraction greater than or equal to 40% died suddenly while taking quinidine than while receiving mexiletine (4/17 vs. 0/24, P less than .02). Mexiletine is as effective as quinidine for treating VC and VT and appears to be less proarrhythmic. It should be considered as an initial choice in the management of VC and VT.

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.

Mexiletine: pharmacology and therapeutic use

Mexiletine is a Class IB antiarrhythmic which has basic and clinical electrophysiologic properties similar to lidocaine. Like other Class I antiarrhythmic agents, mexiletine blocks the rapid inward sodium current responsible for phase 0 of the action potential. It has been noted in the clinical electrophysiology laboratory to have minimal effect on sinus node function and AV nodal and His-Purkinje system conduction. Pharmacokinetic studies have shown that oral absorption is rapid with bioavailability of 80-90%. Mexiletine is predominantly metabolized by the liver with elimination half-life of 9 to 12 hours. The antiarrhythmic effects of the primary drug's metabolites remain to be defined. Hemodynamic studies have shown mexiletine to have a lesser negative inotropic effect than procainamide or disopyramide. Although mexiletine as a single agent successfully suppresses 60 to 80% of spontaneous ventricular arrhythmias, it has lower efficacy in suppression of induced ventricular arrhythmias. Multiple studies have shown that as monotherapy mexiletine is effective in preventing the induction of ventricular tachycardia in approximately 20% of patients. When used in combination with a Class IA antiarrhythmic drug for suppression of induced ventricular arrhythmias, multiple investigators have reported greater efficacy. Neurological side effects (tremor, dizziness, memory loss) occur in approximately 10% of patients while gastrointestinal side effects (nausea, anorexia, gastric irritation) occur in up to 40% of patients. Proarrhythmia or other serious toxicity from the drug is uncommon.

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

Low dose quinidine-mexiletine combination therapy was compared with quinidine monotherapy in 15 patients with frequent ventricular premature complexes and nonsustained ventricular tachycardia in a dose escalation cross-over study. Oral combination therapy was initiated with quinidine gluconate (165 mg) plus mexiletine (150 mg) every 8 h. If ventricular premature complexes were not suppressed greater than or equal to 80% and nonsustained ventricular tachycardia greater than or equal to 90%, the dose was increased to a maximum of 330 mg of quinidine plus 200 mg of mexiletine. Quinidine monotherapy was initiated with 330 mg and escalated to a maximum of 660 mg every 8 h if criteria for effectiveness were not met. Combination quinidine-mexiletine therapy suppressed 80% of ventricular premature complexes in 13 of 14 patients and suppressed 100% of episodes of ventricular tachycardia in 6 of 8 patients (mean quinidine dose 200 +/- 70 mg; mean mexiletine dose 146 +/- 24 mg every 8 h). The mean effective trough quinidine and mexiletine concentration was 1.0 +/- 0.7 and 0.9 +/- 0.4 microgram/ml, respectively. Monotherapy was less effective; that is, greater than or equal to 80% suppression of ventricular premature complexes was observed in 5 of 15 patients and 100% suppression of ventricular tachycardia in 2 of 9 patients. The mean quinidine monotherapy dose was 462 +/- 155 mg every 8 h; the mean quinidine concentration was 1.8 +/- 0.8 microgram/ml. Adverse systemic effects occurred in 3 patients on quinidine-mexiletine therapy and in 11 on quinidine monotherapy.(ABSTRACT TRUNCATED AT 250 WORDS)

Poisoning due to class 1B antiarrhythmic drugs. Lignocaine, mexiletine and tocainide

Since most of the toxicity associated with class 1B antiarrhythmic drugs is dose-related, this review examines adverse effects seen in both therapeutic practice and accidental or premeditated overdose. Toxicity is very common with these agents and can be life-threatening. A high percentage of patients must discontinue therapy because of adverse effects. Mexiletine and tocainide are structural analogues of lignocaine (lidocaine) and toxicity is similar with all 3 drugs. With gradual intoxication (the most common form) central nervous system effects such as lightheadedness, dizziness, drowsiness and confusion are seen first. Seizures and respiratory arrest can occur. Cardiovascular toxicity is manifested by progressive heart block, reduced cardiac contraction, hypotension and asystole. Both mexiletine and tocainide may have proarrhythmic effects. Gastrointestinal toxicity is also common. Shock, hypotension, cardiac failure and beta-blocker therapy reduce lignocaine clearance and enhance the risk of intoxication during routine therapy. Both lignocaine and mexiletine elimination is impaired in severe liver disease while tocainide clearance is reduced in renal failure. Management of toxicity is largely supportive and symptomatic. Lignocaine infusion must be discontinued and decontamination of the gut in the case of oral preparations is recommended. Serious intoxication requires intensive care unit admission. Haemodialysis or haemoperfusion may be helpful in serious lignocaine and tocainide poisoning. In institutions where extracorporeal circulatory assistance is available, massive lignocaine poisoning has been successfully treated with this intervention. In the therapeutic setting serious toxicity can be prevented by close clinical surveillance and appropriate dose reduction in patients with reduced drug clearance. Because of the large interindividual variation in lignocaine pharmacokinetic parameters, therapeutic drug monitoring is recommended if results can be reported quickly. Mexiletine and tocainide have stereoselective metabolism and assays do not distinguish the more active isomers. Therapeutic drug monitoring is less useful in this situation.

Efficacy and safety of flecainide in low-risk patients with chronic ventricular arrhythmias: a two-year follow-up

The long-term efficacy and safety of flecainide (100 to 200 mg twice a day) were evaluated in 21 patients with high-grade, chronic ventricular arrhythmias who responded to and tolerated flecainide at a preliminary evaluation (200 mg, single oral dose). Antiarrhythmic response was evaluated at 3 days and 3, 6, 12, 18, and 24 months. The mean follow-up was 25 +/- 14 months (range 3 to 52). Four patients (19%) were excluded from efficacy analysis because of spontaneous decrease in baseline arrhythmia observed after 12 months of therapy. Effective arrhythmia suppression at both Holter monitoring and during exercise stress testing was maintained in 14 of 17 patients (82%). Mean frequency of premature ventricular contractions remained reduced by more than 95% throughout the follow-up. Five patients discontinued therapy between 3 and 18 months because of drug ineffectiveness (three patients, 18%) or side effects (two patients, 12%). In 12 patients (71%) long-term efficacy and tolerance were demonstrated. In no case was aggravation of arrhythmia or adverse cardiac effects observed. Side effects (5% to 29% of patients during follow-up) were usually minor and easily abolished by dosage reduction. In patients with chronic ventricular arrhythmias, flecainide maintained a favorable ratio between efficacy and side effects during a 2-year follow-up.

Combination of disopyramide and mexiletine for better tolerance and additive effects for treatment of ventricular arrhythmias

The efficacy and tolerance of disopyramide and mexiletine used alone and in combination were studied in 21 patients with frequent (greater than or equal to 30/h) ventricular premature complexes. Ambulatory electrocardiographic monitoring was performed at baseline and during therapy with disopyramide alone, mexiletine alone and a combination of disopyramide and mexiletine. During single drug therapy, the dose of disopyramide was 602 +/- 152 mg/day and that of mexiletine was 738 +/- 144 mg/day. During combination therapy with smaller doses of disopyramide (524 +/- 134 mg/day) and mexiletine (652 +/- 146 mg/day), no patient had side effects. At baseline before therapy, the mean number of ventricular premature complexes per hour, was 608 +/- 757, of couplets per hour was 22.4 +/- 45.8 and of episodes of nonsustained ventricular tachycardia/24 h was 219.7 +/- 758.2. The mean number of ventricular premature complexes per hour was reduced to 156 +/- 217 with disopyramide alone, 188 +/- 298 with mexiletine alone and 76 +/- 144 with combination therapy (p less than 0.05 for combination therapy versus disopyramide or mexiletine alone; p = NS for disopyramide versus mexiletine). Individually, an effective regimen (greater than 83% reduction in ventricular premature complexes and abolition of nonsustained ventricular tachycardia) was found in 5 (24%) of 21 patients during therapy with disopyramide alone, in 3 (14%) receiving mexiletine alone and in 13 (62%) receiving combination therapy (p less than 0.05 for combination therapy versus disopyramide or mexiletine; p = NS for disopyramide versus mexiletine). Thus, the antiarrhythmic effects of disopyramide and mexiletine are additive.(ABSTRACT TRUNCATED AT 250 WORDS)

[Treatment with mexiletine. Clinical and pharmacokinetic studies]

Pharmacokinetics of the antiarrhythmic agent mexiletine were found to be highly variable. Ineffective or toxic doses can be avoided by monitoring mexiletine concentrations in patients plasma. However, the success of antiarrhythmic therapy is mainly determined by the severity of the underlying disease. Therefore, the efficacy of treatment with mexiletine should be controlled by Holter monitoring.

Noninvasive evaluation of indecainide for serious ventricular tachyarrhythmia

Indecainide, a new class 1C agent, was administered to 16 patients with a history of ventricular fibrillation or ventricular tachycardia. Evaluation of drug effect consisted of acute testing with 125 mg followed by a period of maintenance therapy. Efficacy, as evaluated with both ambulatory monitoring and exercise testing, was defined as total elimination of runs of ventricular tachycardia, greater than 90% reduction in couplets and greater than 50% decrease in ventricular premature complex. During acute drug testing 9 of the 16 patients responded to the drug. Four patients did not receive maintenance therapy with indecainide, because of toxic side effects. Of the remaining 12 patients, 7 responded to indecainide based on monitoring, 5 responded judged by exercise testing and 4 when both monitoring and exercise testing were considered. There was no correlation between dose, blood level of drug and effect on arrhythmia. In this small group acute drug testing did not appear to predict the response to the drug during maintenance therapy. Neurologic side effects were reported by 5 patients. Aggravation of arrhythmia occurred in 5 patients, 3 of whom had this complication during acute drug testing and 2 during maintenance therapy. Left ventricular ejection fraction, measured before and during therapy, decreased from an average of 43% to 35% (p less than 0.005). A reduction was observed irrespective of baseline left ventricular function. Indecainide is an effective antiarrhythmic agent in a small number of highly selected patients with serious ventricular arrhythmia, but potentially serious side effects limit its usefulness.

New antiarrhythmic drugs

While controversy still exists as to the precise indications for the treatment of all forms of ventricular arrhythmia, advances in the number and, more importantly, type of antiarrhythmic drugs can provide the clinician with a rational basis for selecting antiarrhythmic drug therapy. A host of new agents with different pharmacokinetic and electrophysiological actions are now available, and can be compared or contrasted to conventional antiarrhythmic agents such as quinidine, procainamide, disopyramide, lignocaine (lidocaine) and bretylium. This review summarises the electrophysiological, haemodynamic, pharmacokinetic, and efficacy and safety data of mexiletine, tocainide, flecainide, encainide, propafenone, amiodarone, sotalol, pirmenol, cibenzoline (cifenline) and ethmozine (moracizine, moricizine), and aims to provide a basis on which clinicians can compare and contrast these agents and form an algorithm for selection of antiarrhythmic drug therapy in the treatment of patients with ventricular arrhythmias.

Long-term efficacy of mexiletine alone and in combination with class Ia antiarrhythmic drugs for refractory ventricular arrhythmias

The efficacy of mexiletine used alone, and in combination with a class Ia antiarrhythmic drug, was assessed in 159 previously drug-refractory patients with ventricular tachycardia (VT) during serial electrophysiologic studies and during long-term (5-year) clinical follow-up. Electrically-inducible ventricular tachycardia was suppressed by mexiletine alone in 23% of patients tested, and a combined antiarrhythmic drug regimen was effective in 29% of the trials performed. Mexiletine was much more likely to be effective in patients presenting with nonsustained VT or ventricular fibrillation than in patients with sustained VT (p less than 0.005). After 1 and 4 years of treatment, 18% and 42% of the patients treated with mexiletine alone had died suddenly or suffered recurrent symptomatic VT, compared to 11% and 25% of patients treated with the combined antiarrhythmic drug regimens (p = NS). Mexiletine therapy was associated with frequent, though readily reversible, adverse reactions. However, mexiletine treatment had to be discontinued permanently in 8 of 92 patients (9%) because of intolerable side effects. We conclude that the added efficacy and possible improved arrhythmia-free survival associated with combining mexiletine with a class Ia agent should be further investigated.

Chronic ventricular arrhythmias: which drug for which patient?

Many agents, including a number of drugs recently approved by the Food and Drug Administration, are now available for the treatment of chronic ventricular arrhythmias. The so-called first-generation agents--quinidine, procainamide and disopyramide--have been used in large numbers of patients for many years, and the safety and efficacy profiles of these drugs are well established. The "second-generation" antiarrhythmic agents recently approved by the Food and Drug Administration offer promising new alternatives; however, their safety and efficacy profiles have yet to be confirmed for broad populations over extended periods of time. Although it is recognized that the choice of agent for treatment of a particular patient is a "therapeutic trial," with an unpredictable outcome of efficacy and adverse effects, certain "descriptors," such as patient age or co-existing medical conditions, are often helpful in determining which agent is most likely to be clinically effective, and which agents are most likely to produce adverse effects. When other medical conditions such as hepatic or renal failure are present, the appropriate choice of drug and dosage is required for optimal management of the arrhythmia and for prevention of overdosage, exacerbation of other medical problems and deleterious interactions. Combination therapy with multiple antiarrhythmic agents is often quite effective for increasing arrhythmia control without increasing adverse effects. However dosage modifications are often necessary when an antiarrhythmic drug is given in conjunction with another such agent, or with agents that also have electrophysiologic activity or modify metabolic or elimination functions. The following report is one clinician's approach for optimizing efficacy and minimizing toxicity while using the difficult class of drugs called antiarrhythmic agents. It will encourage the use of certain drugs before others, based on considerations of efficacy, safety, ease of administration, follow-up, and other factors.

New antiarrhythmic drugs: tocainide, mexiletine, flecainide, encainide, and amiodarone

Tocainide, mexiletine, flecainide, encainide, and amiodarone are antiarrhythmic agents that have recently been approved by the Food and Drug Administration for general use in the treatment of ventricular arrhythmias. All five agents are effective in the treatment of patients with ventricular arrhythmias, whereas encainide, flecainide, and amiodarone are also useful in patients with supraventricular arrhythmias and the Wolff-Parkinson-White syndrome (although not yet approved for these indications). Tocainide and mexiletine are similar to lidocaine and are as effective as quinidine in patients with ventricular arrhythmias. Encainide and flecainide are superior to quinidine for the control of ventricular ectopic beats and as effective as quinidine for patients with ventricular tachycardia. Amiodarone is the most effective agent available for treating patients with ventricular tachycardia, but it is also the most toxic antiarrhythmic agent and should be used only when other antiarrhythmic drugs have not been effective or tolerated.

Antiarrhythmic efficacy of penticainide and comparison with disopyramide, flecainide, propafenone and mexiletine by acute oral drug testing

The antiarrhythmic efficacy of a new class I agent, penticainide, was evaluated by acute oral drug testing and compared in the same patient population with the efficacy of disopyramide, flecainide, mexiletine and propafenone. Twenty-five patients with high-grade chronic ventricular arrhythmias entered the study. During acute oral drug testing, penticainide (7 mg/kg) was effective (more than 90% reduction in ventricular premature complexes and complete abolition of class 4A and 4B arrhythmias) in 17 of 25 subjects (68%). The mean plasma level of the drug at 90 minutes was 4.4 +/- 1.9 micrograms/ml; at the same time increases in the PQ interval (from 168 +/- 27 to 189 +/- 31 ms, p less than 0.0001) and QRS duration (from 89 +/- 14 to 96 +/- 18 ms, p less than 0.001) were observed. The QTc was slightly but not significantly shortened in the overall population; however, in the subgroup with a basally prolonged QTc (n = 8), a significant reduction was observed (from 456 +/- 8 to 440 +/- 18 ms, p less than 0.02). No adverse effects were reported. The antiarrhythmic efficacy of the other drugs tested in the same population was: disopyramide, 12 of 19 (63%); flecainide, 13 of 24 (54%); propafenone, 13 of 24 (54%); and mexiletine, 7 of 20 (35%). Penticainide appears to be a well-tolerated and effective compound of potential value for treatment of ventricular arrhythmias.

Ethmozine (moricizine HCl) therapy for complex ventricular arrhythmias

Moricizine HCl (Ethmozine), a new antiarrhythmic agent, was administered to 102 patients with refractory ventricular fibrillation (n = 31), sustained ventricular tachycardia (VT) (n = 46) or symptomatic nonsustained VT (n = 25). A noninvasive approach utilizing monitoring and exercise testing was used in 82 patients who had a high density of reproducible spontaneous arrhythmia, whereas 20 patients without such arrhythmia required invasive electrophysiologic testing. The dosage of moricizine HCl was 200 mg 3 times daily, and during 5 to 6 days was titrated up to a maximum of 400 mg 3 times daily or 15 mg/kg daily, based on arrhythmia suppression and occurrence of side effects. Criteria for efficacy were a greater than 90% reduction in repetitive ventricular premature beats (couplets and runs of VT) and a greater than 50% reduction in ventricular premature beats when noninvasive methods were used. When electrophysiologic testing was used, the drug was judged effective if it prevented the induction of greater than 2 repetitive responses. Of 75 patients completing noninvasive study, 30 (40%) responded to moricizine HCl therapy, whereas only 1 of 20 patients undergoing electrophysiologic testing responded. There was no difference in moricizine HCl blood levels between responders and nonresponders (0.41 microgram/ml vs 0.43 microgram/ml, difference not significant). Side effects occurred in 28 patients (27%). Most frequent were aggravation of arrhythmia (n = 12), nausea and vomiting (n = 5), central nervous system toxicity (n = 3) and anticholinergic side effects (n = 3). The response rate to moricizine HCl therapy was higher in patients with nonsustained VT (62%) compared with those with sustained VT (19%) or ventricular fibrillation (33%).(ABSTRACT TRUNCATED AT 250 WORDS)

Predictors of antiarrhythmic drug efficacy in patients with malignant ventricular tachyarrhythmias

The relationship between arrhythmia density observed during ambulatory monitoring, left ventricular ejection fraction (EF), and response to antiarrhythmic drug therapy was evaluated in 94 patients presenting with ventricular fibrillation (VF) (n = 20) or ventricular tachycardia (VT) (n = 74). Following baseline studies, an average of 4.9 antiarrhythmic drugs were tested singly in each patient. Univariate and multivariate analyses revealed that the density of VT on baseline ambulatory monitoring and initial left ventricular EF were independent predictors of drug efficacy. The 45 patients with an EF less than or equal to 35% responded to 34 +/- 29% of drugs tested, whereas the 49 with an EF greater than 35% had arrhythmia suppression with 46 +/- 28% of agents (p less than 0.038). Patients exhibiting VT during greater than or equal to 50% of monitoring hours responded to 32 +/- 26% of drugs, whereas those with VT during less than 50% of hours showed arrhythmia suppression with 48 +/- 29% of antiarrhythmic agents tested (p = 0.009). During a mean follow-up period of 12.9 months, the annual sudden death mortality for all patients was 9.3%. However, 8 of the 55 patients responding to less than 50% of drugs tested died suddenly and 17 had recurrent VT. By contrast, only 1 of the 39 patients responding to greater than or equal to 50% of the antiarrhythmic drugs tested died suddenly and two experienced recurrent VT (p = 0.00005).(ABSTRACT TRUNCATED AT 250 WORDS)

Arrhythmogenesis--a European perspective

Arrhythmogenesis as an effect of antiarrhythmic therapy is a relatively recent concern. Satisfactory definitions are lacking, but 2 categories, clinical and technical, can be recognized. Although arrhythmogenesis is an international problem and multifactorial, its expression depends on variables that differ according to geographic location. In Europe, use of antiarrhythmic therapy is more conservative than it is in the U.S. In the U.S., many antiarrhythmic drugs commonly used in Europe are either recently released, are on limited release or are available only in investigational protocols. Mexiletine, class IC agents and sotalol are agents in routine use in Europe. All have arrhythmogenic potential, although this appears lowest with mexiletine.

Aggravation of arrhythmia by antiarrhythmic drugs--incidence and predictors

Aggravation of arrhythmia by antiarrhythmic drugs is a potentially serious complication. In over 1,287 noninvasive drug studies involving 11 antiarrhythmic drugs, arrhythmia aggravation occurred in 117 tests (9%). During 248 electrophysiologic tests, 45 cases (18%) of aggravation occurred. In an attempt to define predictors of this complication, 51 patients with aggravated arrhythmia were compared with 102 patients without this complication. Arrhythmia aggravation was not associated with age, sex, type or extent of heart disease, baseline electrocardiogram, drug-induced changes on electrocardiogram or density of baseline arrhythmia on monitoring or exercise testing. Aggravation with 1 drug did not predict occurrence with another drug of the same class. The only statistically important relation was the type of presenting arrhythmia. Patients with a history of a sustained tachyarrhythmia (ventricular tachycardia or ventricular fibrillation) had a risk of this complication that was 2.5 times greater than that of patients presenting with only nonsustained ventricular tachycardia or ventricular premature beats (p = 0.01). There was also a relation to the presence of left ventricular dysfunction (p = 0.04). For the most part, however, aggravation of arrhythmia is not predictable, and cautious use of antiarrhythmic drugs is essential.

Electrophysiologic effects and clinical efficacy of mexiletine used alone or in combination with class IA agents for refractory recurrent ventricular tachycardias or ventricular fibrillation

The electrophysiologic effects and clinical efficacy of mexiletine used alone or in combination with class IA agents were studied in 35 patients with recurrent sustained ventricular tachycardia (VT) or ventricular fibrillation refractory to nonexperimental antiarrhythmic agents. At baseline before therapy, all patients had inducible VT by programmed stimulation (1 to 3 extrastimuli) and frequent (at least 30/hour) ventricular premature complexes (VPCs) during Holter monitoring. Mexiletine therapy was effective by programmed stimulation (VT no longer inducible or 15 or less beats) in 8 and ineffective in 27 patients. Twenty patients were discharged with mexiletine (14 of whom took an additional class IA agent). The discharge regimen was effective by programmed stimulation in 6 of these 20 patients. In 14 patients the discharge regimen was ineffective by programmed stimulation, but all patients had a marked reduction of ventricular ectopic activity (at least 83% reduction of VPCs and abolition of non sustained VT). During the follow-up period of 18 +/- 13 months (mean +/- standard deviation), 4 patients had recurrences (3 with an ineffective regimen by programmed stimulation and 1 with an effective regimen by programmed stimulation). Arrhythmia-free survival rates at 12 and 24 months were 86% and 77%, as determined by the Kaplan-Meier method, in patients with an ineffective regimen by programmed stimulation, and 80% and 80% in patients with an effective regimen by programmed stimulation (p = 0.979 by log rank test).(ABSTRACT TRUNCATED AT 250 WORDS)

Is programmed stimulation of value in predicting the long-term success of antiarrhythmic therapy for ventricular tachycardias?

We studied the value of programmed stimulation in assessing the efficacy of antiarrhythmic agents in 52 patients with sustained ventricular tachycardia. All patients in this nonrandomized study had ventricular tachycardia inducible by programmed stimulation and also had frequent ventricular premature complexes (greater than or equal to 30 per hour) on Holter-monitor recordings before therapy. The efficacy of antiarrhythmic agents was assessed by both programmed stimulation and Holter recordings during serial drug testing. A regimen was deemed effective according to the programmed-stimulation criteria in 25 patients (Group 1). Twenty-seven patients in whom tachycardia could still be induced during programmed stimulation despite extensive drug trials were discharged on a regimen that caused a marked reduction of ventricular premature complexes according to Holter monitoring (Group 2). In 23 patients no effective drug regimen was identified by either set of efficacy criteria, and these patients were excluded from the present analysis. Follow-up lasted 18.6 +/- 13.9 months. Rates of arrhythmia-free survival at 12 and 24 months were 88 percent and 72 percent, respectively, in Group 1 and 84 percent and 75 percent in Group 2 (P = 0.637). We conclude that demonstration of antiarrhythmic efficacy by programmed stimulation predicts a good clinical outcome, that inefficacy as shown by the programmed-stimulation protocol used in this study may not preclude a good outcome if there is a marked reduction of spontaneous ventricular premature complexes on Holter monitoring, and that randomized trials should be conducted to validate the results of this observational study.

Intolerance and ineffectiveness of mexiletine in patients with serious ventricular arrhythmias

Fifty-one patients were treated with mexiletine over 10.4 +/- 16 months. The clinical arrhythmia in 25 (49%) was ventricular fibrillation (VF), 11 (22%) had sustained ventricular tachycardia (VT), and 15 (29%) had symptomatic nonsustained VT. Ischemic heart disease was present in 33 patients (66%), cardiomyopathy in nine (17%), and valvular or congenital heart disease in nine (17%). Only six (12%) remain on the drug. Arrhythmias recurred in 21 patients (41%): seven (14%) with VF, three (5%) with sustained VT, and 11 (22%) with symptomatic nonsustained VT. Intolerable side effects occurred in another 17 (33%). Seven patients (14%) died from nonarrhythmic-related deaths while taking mexiletine. Mexiletine was combined with a conventional type IA antiarrhythmic agent in 25 patients (49%). In 12 of these 25 patients (48%), ventricular arrhythmias recurred. These findings were not significantly different from those of the group treated with mexiletine alone, where arrhythmias recurred in 9 of 26 patients (35%) (p = NS). Thus mexiletine, alone or in combination with a type IA antiarrhythmic agent, has limited clinical utility in patients with life-threatening ventricular arrhythmias.

Discordance between ambulatory monitoring and programmed stimulation in assessing efficacy of mexiletine in patients with ventricular tachycardia

Programmed electrical stimulation (PES) and 24-hour Holter monitoring were compared in 30 patients with ventricular tachycardia (VT) or ventricular fibrillation (VF) before and during treatment with mexiletine. Before treatment, all patients had greater than or equal to 30 ventricular premature complexes (VPCs)/hr and 22 patients had nonsustained VT on Holter. All had inducible sustained VT by PES (one to three extrastimuli). Mexiletine was effective in only 23% by PES criteria (VT no longer inducible or less than or equal to 15 beats in duration and effective in 57%, 57%, and 73% by Holter criteria I, II, and III, respectively (Holter I greater than or equal to 50% reduction of VPCs, greater than or equal to 90% reduction of couplets and abolition of nonsustained VT; Holter II greater than or equal to 83% reduction of VPCs and abolition of VT; Holter III abolition of VT in patients who had VT during baseline Holter). Results of PES and Holter were discordant in 67%, 60%, and 55% (PES vs Holter I, II, and III, respectively). The majority (greater than or equal to 75%) of the discordance occurred due to mexiletine appearing effective by Holter criteria but ineffective by PES criteria (suggesting insensitivity of efficacy by Holter criteria and/or nonspecificity of induced VT during treatment with mexiletine).

CONCLUSIONS

PES and Holter are discordant in assessing efficacy of mexiletine (p less than 0.05). Efficacy of mexiletine by Holter criteria is easier to achieve than efficacy by PES. The discordance between the two methods, both with very good reported predictive values, calls for randomized clinical follow-up studies to determine sensitivity and specificity of each method in assessing efficacy of mexiletine.

Mexiletine: a new type I antiarrhythmic agent

Mexiletine is a type I antiarrhythmic drug that is structurally similar to lidocaine. Mexiletine has considerable potential for causing neurologic, cardiac, or gastrointestinal side effects. However, mexiletine does not undergo clinically significant first-pass metabolism and, thus, has good oral bioavailability. Mexiletine has a large and variable volume of distribution and an elimination half-life ranging from 6 to 12 hours. Mexiletine disposition is probably altered in patients with heart failure, liver disease, and severe renal dysfunction. Efficacy and toxicity are not well correlated with mexiletine serum concentrations. Mexiletine is as effective as traditional antiarrhythmics in the treatment of premature ventricular contractions. However, in patients with drug-refractory inducible ventricular tachycardia, mexiletine is usually ineffective when used alone. When mexiletine is combined with other antiarrhythmic agents, a significantly higher percentage of patients with this difficult arrhythmia have a good response. Mexiletine is a potentially important addition to the existing antiarrhythmic drugs currently available, but its place in the clinical setting and in therapeutic drug monitoring is not well defined at this time.

Mexiletine and tocainide: does response to one predict response to the other?

Mexiletine and tocainide were administered to 79 patients to determine whether the response to one of these drugs would predict the effect of the other. In 57 patients, the two agents were evaluated noninvasively with monitoring and exercise testing, and efficacy was judged by the suppression of spontaneous ventricular arrhythmia. In the remaining 22 patients, electrophysiologic testing was performed and efficacy was defined as the inability to induce more than two repetitive ventricular premature beats. An equal number of patients responded to mexiletine and tocainide (38 versus 39%). However, in only 42 patients (53%) were the results concordant. There was no difference in concordance when the results were analyzed by method of drug evaluation, left ventricular ejection fraction or etiology of presenting arrhythmia. It is concluded that mexiletine and tocainide have different clinical effects and must be evaluated individually.

Short- and long-term therapy with tocainide for malignant ventricular tachyarrhythmias

Tocainide was administered to 228 patients referred for treatment of recurrent ventricular tachyarrhythmias that were refractory to therapy with conventional antiarrhythmic drugs. After baseline studies, 1200 to 2400 mg tocainide/day was given for 4 days. Tocainide was effective in 49% of 180 patients evaluated with monitoring and exercise testing and in 35% of 48 patients undergoing electrophysiologic testing. No clinical parameter predicted the response to tocainide, although there was a correlation with the effect of lidocaine. Tocainide was selected for long-term treatment in 73 patients who were followed for an average of 26.4 months (range 1 to 92 months). The incidence of sudden death was 4.3% per year and two patients had nonfatal recurrence of arrhythmia. It is concluded that tocainide is effective and well tolerated during long-term use if therapy is evaluated carefully and is individualized.

Pharmacology and clinical use of mexiletine

Mexiletine is an antiarrhythmic agent with structural and electrophysiologic properties similar to those of lidocaine. Mexiletine decreases ventricular automaticity while shortening both action potential duration and effective refractory period. The drug may be administered orally or intravenously. Hepatic metabolism is the major route of elimination. The elimination half-life is approximately 10 hours, but longer in patients with acute myocardial infarction, chronic congestive heart failure or hepatic insufficiency. Mexiletine suppresses ventricular ectopy in the acute phase of myocardial infarction. The drug is effective for some patients in whom lidocaine has failed. It suppresses chronic ventricular ectopy and is well tolerated in approximately two-thirds of stable outpatients treated with this agent. In that population, mexiletine is comparable in efficacy to quinidine, procainamide and disopyramide. It is effective in 30-50% of patients with ventricular arrhythmias refractory to other antiarrhythmic drugs. In patients with refractory arrhythmias, the efficacy of mexiletine may be enhanced by combination with propranolol, quinidine or amiodarone. Adverse reactions limit use of mexiletine in approximately 20% of patients. Gastrointestinal and central nervous system side effects are the most common. Mexiletine does not depress myocardial function. Aggravation of arrhythmias is uncommonly observed. The usual intravenous dose of mexiletine is 150-250 mg over at least 10 minutes. Long-term oral dosages are usually 200-300 mg 3 or 4 times daily.