Mexiletine

The efficacy and safety of first-line therapies for preventing chronic post-surgical pain: a network meta-analysis

Background

Due to conflicting evidence regarding first-line therapies for chronic post-surgical pain (CPSP), here we comparatively evaluated the efficacy and safety of first-line therapies for the prevention of CPSP.

Materials and Methods

MEDLINE, EMBASE, and Cochrane CENTRAL databases were searched for randomized, controlled trials (RCTs) of systemic drugs measuring pain three months or more post-surgery. Pairwise meta-analyses (a frequentist technique directly comparing each intervention against placebo) and network meta-analyses (a Bayesian technique simultaneously comparing several interventions via an evidence network) compared the mean differences for primary efficacy (reduction in all pain), secondary efficacy (reduction in moderate or severe pain), and primary safety (drop-out rate from treatment-related adverse effects). Ranking probabilities from the network meta-analysis were transformed using surface under the cumulative ranking analysis (SUCRA). Sensitivity analyses evaluated the impact of age, gender, surgery type, and outlier studies.

Results

Twenty-four RCTs were included. Mexiletine and ketamine ranked highest in primary efficacy, while ketamine and nefopam ranked highest in secondary efficacy. Simultaneous SUCRA-based rankings of the interventions according to both efficacy and safety revealed that nefopam and mexiletine ranked highest in preventing CPSP. Through the sensitivity analyses, gabapentin and ketamine remained the most-highly-ranked in terms of efficacy, while nefopam and ketamine remained the most-highly-ranked in terms of safety.

Conclusions

Nefopam and mexiletine may be considered as first-line therapies for the prevention of CPSP. On account of the paucity of evidence available on nefopam and mexiletine, gabapentin and ketamine may also be considered. Venlafaxine is not recommended for the prevention of CPSP.

Arrhythmogenic effects of mexiletine in infarcted Purkinje tissues

The electrophysiologic effects of mexiletine on canine subendocardial Purkinje's fibers were examined 24 hours after a two-stage ligation of the left anterior descending coronary artery. Transmembrane potentials were recorded simultaneously in normal (NZ) and infarcted (IZ) zones before and during superfusion with mexiletine. Mexiletine (3, 6, and 9 mg/l) reduced the values of maximum diastolic potential (MDP), action potential amplitude (APA), and maximum rate of phase 0 depolarization (Vmax). The effective refractory period (ERP) was lengthened by the drug. These findings are consistent with the actions of class IB antiarrhythmic drugs. In 42% of the preparations examined, repetitive responses were induced at or near the ERP during superfusion with 3 mg/l mexiletine. These extra responses were no longer elicited during superfusion with 6 mg/l mexiletine. A mechanism for the origin of these reentrant-type arrhythmias based on the action of mexiletine is presented.

Effect of mexiletine, amiodarone and disopyramide on the excitability and refractoriness of canine cardiac fibers: possible relation to antiarrhythmic drug action and classification

We tested the hypothesis of Campbell that the effect of the sodium channel-blocking antiarrhythmic drugs on postrepolarization refractoriness i.e., relation between action potential duration (APD) and effective refractory period (ERP) is determined by the drug's effect on the recovery from Vmax block. We studied the effects of two antiarrhythmic drugs with fast (mexiletine, amiodarone), and one with slow (disopyramide) kinetics of recovery from Vmax block, at two different basic cycle lengths (BCL), on ERP/APD ratio in cardiac dog Purkinje and ventricular muscle fibers. ERP was measured using stimuli of 2 ms duration and 1.0 to 5.0 times diastolic threshold strength. The three drugs altered the kinetics of recovery from Vmax block in the manner previously reported by us and other investigators. In both fiber types, mexiletine increased and the other two drugs did not change the ERP/APD ratio. We concluded that the magnitude of postrepolarization refractoriness could not be predicted from the kinetics of the Vmax block. Also, the effect of the drug on the ERP/APD ratio could be altered by changes in the stimulus strength and the BCL.

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)

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.

Pharmacologic treatment of cardiac arrhythmias: 25 years of progress

This review of practical and theoretical advances in antiarrhythmic drug therapy consists of four parts. Part 1, on clinical applications, compares the approaches to treatment 25 years ago with those of today, examines the current status of antiarrhythmic drugs used 25 years ago, reports on drugs approved for clinical use during the past 25 years, reviews new experimental drugs and suggests an approach to classification of antiarrhythmic drugs. Part 2 summarizes the contributions of cellular electrophysiology to the understanding of drug action, with emphasis on the drug-induced block of the voltage- and time-dependent properties of the rapid sodium channel. The subsequent section contains a brief discussion of the impact made by the new knowledge and the new diagnostic technology on the contemporary practices. The main conclusions are 1) that the more rational approach to treatment has benefited proportionately more patients with supraventricular than with ventricular arrhythmias, and 2) that new advances have made it possible to design successful treatments for certain patients with problems that could not be resolved in the past.

Mexiletine vs. lignocaine in the management of ventricular arrhythmias after open-heart surgery

We made an open comparison of lignocaine and mexiletine in the treatment of ventricular arrhythmias occurring after open-heart surgery. Thirty patients whose arrhythmia did not respond to correction of metabolic disturbances were randomly allocated to receive treatment either with lignocaine or with mexiletine in fixed dosage schedules (15 in each group). Failure to control the rhythm or recurrent abnormality led to administration of a further dose and, if this was unsuccessful, to crossover to the alternative agent. The two drugs were comparable in efficacy, but mexiletine was slightly more effective when administered after lignocaine than the converse.

New drugs for treating cardiac arrhythmias

The new and potent antiarrhythmic drugs herald an exciting era in the treatment of cardiac arrhythmias. Encainide, tocainide, and mexiletine are effective in treating acute and chronic ventricular arrhythmias. Verapamil promises to be the drug of choice for paroxysmal supraventricular tachycardia. Acetubolol provides the advantages of selective beta receptor blockade and has minimal influence on pulmonary function. Aprindine and amiodarone block conduction in accessory pathways and are very suitable for treating tachycardias associated with Wolff-Parkinson-White syndrome. Ethmozin is a phenothiazine derivative with potent antiarrhythmic effects. Many of these new agents are being used with striking success abroad and at specialized treatment centers for experimental research in the United States.

Torsades de pointes as a manifestation of mexiletine toxicity

An episode of torsades de pointes, an unusual ventricular tachyarrhythmia, developed in a 59-year-old coronary patient who was treated with 100 mg. four times a day mexiletine orally. The PR, QRS, and QT intervals were normal. The ventricular arrhythmias resembled in part, the patient's previous ventricular premature complexes, but there were some relevant morphological differences. The plasma electrolytes were within normal limits. Mexiletine, which is chemically and electrophysiologically similar to lidocaine, probably caused this arrhythmia. Although mexiletine is a useful antiarrhythmic drug, it should be added to the list of drugs associated with atypical ventricular tachycardia.