Effect of antiarrhythmic drugs on defibrillation threshold: case report of an adverse effect of mexiletine and review of the literature

Antiarrhythmic agents can influence defibrillation threshold (DFT). Basic research suggests that some class I drugs may have deleterious effects by raising defibrillation energy requirements. Evaluation of this problem in man has been limited to reports of patients who were more difficult to cardiovert or defibrillate after treatment with amiodarone and class IC agents. In the present report, mexiletine appeared to be the probable cause of an important elevation of DFT in a patient undergoing replacement of a malfunctioning automatic implantable cardioverter/defibrillator (AICD). This report and the accompanying literature review suggest that more information at both the basic and clinical levels is required. Retesting of device efficacy in terminating induced arrhythmia in the laboratory appears prudent in patients who require antiarrhythmic drug therapy subsequent to AICD implantation.

Comparative efficacy and safety of oral mexiletine and quinidine in benign or potentially lethal ventricular arrhythmias

The antiarrhythmic efficacy and safety of oral mexiletine hydrochloride and quinidine sulfate were compared at 29 clinical centers in a double-blind, parallel-group trial involving 491 patients with benign or potentially lethal ventricular arrhythmias. Responders were defined as those who had at least a 70% reduction in the frequency of ventricular premature complexes (VPCs) that persisted for 12 weeks, and who experienced no intolerable side effects that required discontinuation of therapy. Of the patients available for analysis, 71 of 232 (31%) in the mexiletine and 73 of 225 (32%) in the quinidine group met these criteria. The dose range used for mexiletine was 200 to 400 mg every 8 hours, and that for quinidine 200 to 400 mg every 6 hours. More than half of the patients in each group were successfully treated with the smallest dose (200 mg every 8 hours mexiletine vs 200 mg every 6 hours for quinidine). Quinidine significantly prolonged the QT interval, whereas mexiletine did not. Proarrhythmic reactions were recorded in 18 of 221 (9%) patients taking quinidine and 10 of 217 (5%) patients taking mexiletine. There was no difference in the incidence of adverse reactions between the 2 groups; in both, the most common side effects were related to the gastrointestinal and central nervous systems. Mexiletine thus represents an alternative to quinidine for the treatment of patients with ventricular arrhythmias.

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.

Mexiletine: an effective antiarrhythmic drug for treatment of ventricular arrhythmias in congenital heart disease

The use of antiarrhythmic drugs to suppress ventricular arrhythmias in pediatric patients with a structurally or hemodynamically abnormal heart appears to improve long-term prognosis. The previously successful use of phenytoin to treat serious ventricular arrhythmias led to the investigation for an alternative antiarrhythmic agent, in the same antiarrhythmic drug class, for those patients who develop side effects or become intolerant to phenytoin's antiarrhythmic effect. Forty-two children and young adults (age range 5 months to 34 years, mean 15.5 years) were treated with mexiletine. Arrhythmias treated were ventricular tachycardia (25), ventricular couplets (8), multiform ventricular premature beats (4) and frequent uniform ventricular premature beats (5). Anatomic diagnoses included congenital heart disease (postoperative in 26, unoperated in 2), cardiomyopathy (7), no heart disease (4) and other (3). Thirty-three patients had been previously treated with 1 to 5 (mean 1.6) antiarrhythmic drugs. In the short term, ventricular arrhythmias were effectively suppressed in 30 (71%) of all 42 patients treated. During follow-up (ranging to 42 months, median 10.6), 18 (60%) of the 30 acute responders continued to have excellent control. Early suppression of ventricular arrhythmias was more effective in patients with congenital heart disease (89%) than in those with cardiomyopathy (29%) or no heart disease (43%) (p less than 0.01). Initial complexity of ventricular ectopic activity had no effect on treatment results. Of 25 patients previously treated with phenytoin, in whom alternative antiarrhythmic therapy was required, 40% had long-term arrhythmia control when treated with mexiletine. Mexiletine therapy was terminated for side effects in only five patients (12%). Mexiletine is recommended for young patients with congenital heart disease and serious ventricular arrhythmias.

[Anti-arrhythmia effectiveness and tolerance of retard in comparison with standard mexiletine]

In a controlled randomized cross-over trial, 21 patients with coronary artery disease and frequent ventricular arrhythmias were studied to test the efficacy and tolerance of mexiletine 200 mg t.i.d. in comparison to a released application form of mexiletine perlongettes 360 mg b.i.d. During 24-hour Holter monitoring, all patients but one showed more than 30 ventricular premature beats/h; additionally, in 16 patients, complex ventricular arrhythmias (Lown class IV) were documented. In all patients each medication was given for 5 days. Before treatment and during both medication periods, a 4 days' wash-out period was interposed. Mexiletine and mexiletine perlongettes each resulted in a suppression of ventricular ectopy of more than 84% in 10/21 patients (47%); in two patients the response was different. The mean reduction rate in all patients was 68% for mexiletine and 64% for mexiletine perlongettes. In the responder group, the mean reduction rate amounted to 95% under both medications. Ventricular pairs and tachycardia were reduced by more than 90%. Plasma concentration under mexiletine perlongettes was slightly higher, as compared to the standard form of mexiletine; however, under mexiletine, significant changes of plasma concentration were observed during the day only when the standard form was used. Side effects were observed in 8/21 patients (38% for mexiletine) and in 5/21 patients (24% for mexiletine perlongettes). These were mainly gastrointestinal or neurological, but were mild in all patients and did not necessitate discontinuation of the medication in any patient.(ABSTRACT TRUNCATED AT 250 WORDS)

Mexiletine use in pregnancy and lactation

Treatment of arrhythmias during pregnancy is complicated by insufficient information on the effects of the drug on the fetus or possible alterations of the drug's pharmacodynamics in the mother. The use of mexiletine, a newly introduced antiarrhythmic agent, during the entire course of pregnancy and subsequent lactation is presented.

Relationship between plasma mexiletine levels at steady-state. Presence of ventricular arrhythmias and side effects

The relationships between plasma mexiletine levels and the presence of ventricular arrhythmias and side effects were studied on patients from IMPACT (International Mexiletine and Placebo Antiarrhythmic Coronary Trial). 630 patients who had suffered a myocardial infarction were randomized between placebo and mexiletine. Plasma levels were measured 1 month after the beginning of treatment. Arrhythmia findings (presence or absence of premature ventricular contractions (PVCs), couplets, runs, bigeminy, trigeminy, multiformity and various combinations) were assessed from 24-h ambulatory ECG recordings. The empirical logistic transform was used for modeling the relationships. For all these variables, except the presence of PVCs, trigeminy and runs, the association with plasma level was significant: the higher the plasma level, the lower the rate of occurrence of the particular arrhythmia. This was true whether or not the patient had the arrhythmia at baseline. Analyses based on the same model showed a significant correlation between plasma level and tremor, constipation, sexual problems and the presence of at least one side effect. As the levels of mexiletine at which side effects become frequent are in the same range as those necessary to suppress arrhythmias, the therapeutic range is narrow and individual dose adjustment should preferably be made.

Comparison of intravenous mexiletine and lidocaine for the treatment of ventricular arrhythmias

The efficacy and safety of intravenous loading of mexiletine was compared to lidocaine in patients with ventricular premature depolarizations (VPDs). Seventeen men and five women, average age 63 years, completed this randomized parallel study. Twelve patients received mexiletine intravenously at (5 to 10 mg/min) until greater than or equal to 95% VPD suppression was achieved or a total of 450 mg of drug was given. The average loading dose of mexiletine was 4.4 mg/kg, at an infusion rate of 0.1 mg/kg/min. Ten patients received lidocaine (1 mg/kg) given over 3 minutes, with a second similar bolus given if after 10 minutes greater than or equal to 95% VPD suppression was not achieved. Total VPDs were determined for the 60 minutes before drug administration, during drug infusion, and 60 minutes thereafter. Eleven of 12 (92%) patients receiving mexiletine were full responders (greater than or equal to 95% suppression) and one was a partial responder (greater than or equal to 75% greater than or equal to 95% suppression). Five of 10 lidocaine patients (50%) were full responders, three (30%) were partial responders, and two failed to respond. At peak suppression, mexiletine reduced mean VPD from 37 +/- 33/5 minutes (mean +/- S.D.) to 0.8 +/- 0.9/5 minutes (p less than 0.01) and lidocaine decreased mean VPDs from 28 +/- 47/5 minutes to 4.7 +/- 2.2/5 minutes (p less than 0.01). Mexiletine resulted in greater suppression of VPDs than lidocaine in terms of mean percent reduction (96% vs 68%, p less than 0.01). All lidocaine patients had therapeutic plasma levels (range 1.6 to 3.5 micrograms/ml).(ABSTRACT TRUNCATED AT 250 WORDS)

[Esophageal ulcerations induced by mexiletine hydrochloride]

The author reports a case of drug induced esophagitis secondary to mexiletine hydrochloride. At the time of gastroscopy, the patient is asymptomatic. Ulcerations are located at the level of the cervical esophagus and are reddish in color. The evolution is favorable. Prevention of such incidents is easy: ingestion of the medication while standing up with enough water (60 ml).

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.

Adverse reactions to antiarrhythmic drugs during therapy for ventricular arrhythmias

We analyzed the incidence of adverse reactions to antiarrhythmic drugs in 123 consecutive patients with a history of sustained ventricular tachycardia or ventricular fibrillation. Blood levels were measured serially and were maintained within the usual therapeutic range. Minor reactions were defined as those that required dosage reduction and major reactions as those that required drug discontinuation or permanent pacing for bradycardia. A total of 237 individual, oral drug trials were evaluated in the 123 patients. Adverse reactions were noted in 79 trials (33%). Fifty-nine (48%) of the 123 patients had one or more adverse reaction. Major reactions were noted in 36 patients (29%). Adverse effects occurred during 49% of trials with mexiletine hydrochloride, 44% of trials with amiodarone, 24% of trials with procainamide hydrochloride, and 18% of trials with quinidine sulfate or gluconate. In conclusion, clinically significant adverse reactions are common during drug therapy for ventricular arrhythmias. These observations indicate that with the drugs used in this study, an acceptable risk-benefit ratio will be possible only in patients at a significant risk for a symptomatic arrhythmia. Antiarrhythmic drug therapy in patients at low risk for serious arrhythmia should be discouraged.

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.

Dose independent pharmacokinetics of mexiletine in healthy volunteers

In 12 healthy volunteers who received orally 100, 200, 300, 400 and 600 mg mexiletine at weekly intervals, the maximum plasma concentration of mexiletine and AUC increased linearly with the dose of mexiletine. Between doses there were no significant differences in the values for clearance and volume of distribution of mexiletine but there were for plasma elimination half-life. These results indicate that the kinetics of mexiletine are linear.

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.

Cirrhosis of the liver markedly impairs the elimination of mexiletine

To study the effects of cirrhosis of the liver on the pharmacokinetics of mexiletine a single i.v. dose of 200 mg was administered to six cirrhotic patients and to six healthy controls. The distribution of mexiletine in both study groups was similar, as indicated by similar values of V1 and Vss, but it tended to occur more slowly in the cirrhotics. The plasma protein binding of mexiletine was unchanged in the patients with cirrhosis. The elimination of mexiletine was markedly retarded in the cirrhotics, as indicated by its lower total clearance (2.31 vs. 8.27 ml/kg/h,) lower total elimination rate constant (0.059 vs 0.353 h-1), and longer elimination half-life (28.7 vs 9.9 h). The antipyrine half-life was 38.3 h in the patients and 14.7 h in the controls. One healthy volunteer had a Morgagni-Stokes-Adams type of syncopal attack 5 min after administration of mexiletine due to disturbance of AV conduction induced by the drug. Thus, on a pharmacokinetic basis the loading dose of mexiletine need not be modified in cirrhotic patients, whereas the maintenance dosage should be reduced to one fourth - one third of the usual dose.

Mexiletine: double-blind comparison with procainamide in PVC suppression and open-label sequential comparison with amiodarone in life-threatening ventricular arrhythmias

The antiarrhythmic effects of mexiletine (n = 14) were compared to procainamide (n = 16) by a double-blind parallel protocol in 30 patients (group I) with frequent premature ventricular contractions (PVCs) (greater than 20/hr), and to amiodarone by an open-label sequential approach in 25 patients (mean left ventricular ejection fraction of 32.6 +/- 13.4%) with life-threatening ventricular arrhythmias (group II) resistant to two or more conventional agents. The predetermined end point of therapy in group I patients was met in 6 of 14 (43%) given mexiletine, with 7 (50%) requiring drug discontinuation for severe gastrointestinal or central nervous system side effects and only 3 of 16 patients (19%) given procainamide, with 5 (31%) developing limiting side effects. Increases in dose led to a higher efficacy rate for PVC suppression with a corresponding increase in side effects with mexiletine; with procainamide, the higher dose was not associated with greater PVC suppression. In group II patients, mexiletine was effective in 4 (16%), with one patient discontinuing the drug during long-term therapy; mexiletine was ineffective in 16 (64%) and early side effects developed in 5 (20%). Patients not responding to or not tolerating mexiletine were given amiodarone; 20 of 21 (95%) responded with arrhythmia control after the loading dose. During a mean follow-up period of 2 years, sudden death occurred in two patients, death from heart failure in two, and death from subarachnoid hemorrhage in one patient; 15 (75%) patients are alive and free of arrhythmia.(ABSTRACT TRUNCATED AT 250 WORDS)