Long-term treatment of ventricular arrhythmias with oral mexiletine

Pharmacokinetics of mexiletine in renal insufficiency

1 The aim of this study was to evaluate the influence of renal insufficiency on the plasma pharmacokinetics of mexiletine, a new antiarrhythmic agent, in human beings. 2 Mexiletine was administered orally three times daily for 10 days to 15 patients with chronic renal failure (creatinine clearance lower than 30 ml/min) and to 9 subjects with normal renal function. 3 The use of low doses of mexiletine was possible owing to the development of a new fluorescence h.p.l.c. method with a limit of sensitivity lower than 20 gn/ml. 4 Our results clearly indicate that the plasma kinetics of mexiletine are not modified when the renal clearance of creatinine is higher than 10 ml/min.

Determination of mexiletine in biological fluids by high-performance liquid chromatography

A high-performance liquid chromatographic method for the determination of the anti-arrhythmic drug mexiletine in human plasma, urine, and cerebrospinal fluid is described. Following extraction with diethyl ether, mexiletine and the internal standard 4-methylmexiletine were derivatized with 2,4-dinitrofluorobenzene. Analyses were performed using an alternating on-column enrichment technique on small Perisorb RP-2 30-40 micrometers pre-columns with pre-column backflushing for direct injection onto the analytical column of Spherisorb ODS 5 micrometers. Complete separation from endogenous constituents of plasma, urine or cerebrospinal fluid was achieved by isocratic reversed-phase ion-pair chromatography with 1-heptanesulfonic acid (0.005 M; PIC B7)-acetonitrile-tetrahydrofuran (42:48:10, v/v) as eluent. Interferences from other drugs were not observed. The limit of detection was 10 ng/ml (C.V. 6.5%). Day-to-day coefficients of variation were below 9%. The applicability of this rapid method for pharmacokinetic studies and clinical routine is demonstrated.

Mexiletine, a new antiarrhythmic agent, for treatment of premature ventricular complexes

This double-blind crossover study was designed to compare the safety and efficacy or mexiletine, a new class I antiarrhythmic agent, with those of a placebo in reducing premature ventricular complexes. Twelve patients who had a median of 294 such complexes/hour were admitted to the study. Eleven completed 4 weeks of trial with mexiletine and placebo with ambulatory electrocardiographic (Holter) recordings taken at the end of each treatment period. The doses given were designed to reduce the frequency of premature ventricular complexes by 50 percent or more from the baseline value. Mexiletine significantly reduced the rate of premature ventricular complexes by comparison with placebo (-66 percent versus 3 percent, p = 0.032). In addition, mexiletine reduced the median number/hour of ventricular couplets observed. After 4 weeks of therapy, 2, 2, 1 and 6 patients, respectively, were taking 100, 200, 300 and 400 mg of mexiletine every 8 hours. Mexiletine produced no significant change in baseline values including electrocardiographic intervals, blood pressure or heart rate. The most frequently observed adverse effects were digestive difficulties (eight patients taking mexiletine, four taking placebo) and central nervous system effects (seven taking mexiletine, five taking placebo). These data show the efficacy and safety of mexiletine in the treatment of premature ventricular complexes in a majority of patients.

Gas-liquid chromatographic determination of mexiletine in human serum with nitrogen sensitive detection

A simple and rapid method for the quantitative determination of mexiletine, using gas-liquid chromatography with nitrogen sensitive detection, is described. Only one extraction step is needed, the recovery is between 92-96% and the precision varies between 2.0--5.5%. The lower limit of detection reached 0.5 micro mol/1. During routine handling the method was easy, quick and cheap.

Plasma mexiletine concentrations following combined oral and intramuscular administration

Mexiletine in doses of 50, 100 and 400 mg was administered by intramuscular injection to a healthy subject and the resulting plasma concentrations were compared with those after 100 mg given intravenously. The bioavailability of mexiletine given by this route is complete and the kinetics are linear with dose. Plasma mexiletine concentrations resulting from 200 mg given orally with either two 4-ml intramuscular injections each containing 100 mg (Mexitil--for intravenous use) or one 2-ml intramuscular injection of an experimental preparation containing 200 mg were compared in 3 and 6 normal subjects respectively. Plasma levels within the therapeutic range of 0.75-2 microgram/ml were attained at mean times of 28.7 and 42.5 min respectively. Apart from raised plasma creatine phosphokinase levels (as would be expected following an intramuscular injection) the tolerability of intramuscular mexiletine injections was satisfactory. Further studies in patients will be required to determine whether the combined oral and intramuscular administration of mexiletine is of value in acute myocardial infarction.

Mexiletine for refractory-ventricular arrhythmias: results using serial electrophysiologic testing

Mexiletine was administered during serial drug testing to 35 patients with electrically inducible ventricular arrhythmias and to 6 with recurrent ventricular tachycardia that could not be induced or terminated by programmed cardiac stimulation. All patients had arrhythmias resistant to all conventionally available agents. Electrically induced arrhythmias were completely suppressed during mexiletine therapy in 13 patients. In 12 patients no antiarrhythmic regimen was completely suppressive and in 7 of these mexiletine favorably modified the response to programmed stimulation. In four of six patients with frequent episodes of spontaneous ventricular tachycardia that were not inducible by programmed cardiac stimulation, arrhythmia was controlled by mexiletine. The presence of complete arrhythmia suppression with mexiletine during acute testing accurately predicted long-term freedom from recurrent arrhythmia in 16 of 17 patients over a mean follow-up period of 12.6 +/- 6 months. Severe adverse neurologic effects were noted early during mexiletine therapy in three patients, but no patient discharged on such therapy experienced major adverse effects. The study demonstrates that mexiletine can provide well tolerated effective prophylaxis against recurrent ventricular arrhythmias in a significant proportion of patients resistant to conventional drugs.

Mexiletine therapy in 15 patients with drug-resistant ventricular tachycardia

Mexiletine therapy was administered to 15 patients with chronic and recurrent episodes of ventricular tachycardia or ventricular fibrillation. All patients were intolerant of or had arrhythmias resistant to conventional antiarrhythmic agents. At maximal dosages of mexiletine 2 patients had more than 90 percent reduction in frequency of premature ventricular complexes, whereas 11 patients had less than 50 percent reduction, as measured on 24 hour electrocardiographic recordings. Mexiletine was unsuccessful in preventing or abolishing ventricular tachycardia in 11 patients. Adverse side effects occurred in nine patients (60 percent) and were severe enough to necessitate discontinuation of therapy in six patients (40 percent). Side effects appeared to be dosage-related. Pharmacokinetic analysis indicated a mean elimination half-life of 12.6 +/- 1.6 hours following oral administration of mexiletine. In the patients studied, mexiletine exhibited limited antiarrhythmic efficacy and was associated with frequent adverse side effects.

Suppression of chronic ventricular arrhythmias with propranolol

The antiarrhythmic efficacy of propranolol was evaluated in 32 patients with chronic high frequency ventricular arrhythmias in a placebo-controlled protocol. After a placebo control period, propranolol was begun and the dosage increased sequentially until arrhythmia suppression was achieved, side effects appeared, or a maximum dosage of 960 mg/day was reached. Computerized analysis of ambulatory recordings was used to quantify the arrhythmias. Twenty-four patients had 70--100% arrhythmia suppression at plasma levels ranging from 12--1100 ng/ml (end of dosing interval). Eight patients in this group had frequent episodes of ventricular tachycardia that were totally suppressed at or below the dosage that produced greater than or equal to 70% suppression of ventricular ectopic depolarizations (VEDs). A biphasic dose-response curve was seen in five patients who responded with a decrease in arrhythmia frequency in the lower ranges of dosages but had increased frequency of ectopic rhythms as the dosage was increased above the optimal level. Only one-third of patients responded at doses less than or equal to 160 mg/day. However, with dosages of 200--640 mg/day, an additional 40% responded. Propranolol appears to control ventricular arrhythmias safely and effectively in many patients. The finding that the antiarrhythmic effect in many patients required plasma concentrations greater than those that produce substantial beta-adrenergic blockage raises a question whether blockade of cardiac beta receptors can directly account for all of the antiarrhythmic actions of propranolol.

The clinical pharmacology of mexiletine

1. Mexiletine was given to 156 patients by intravenous or oral routes of administration. 2. There was great interpatient variation in kinetics and plasma concentrations with both routes of administration. 3. The mean volume of distribution was 6.63 l/kg. The mean plasma elimination haf-life after chronic oral therapy was 11.31 h. 4. Plasma concentrations between 0.75 and 2.00 microgram/ml were usually effective. Within this therapeutic range severe side effects were uncommon. 5. Plasma concentrations within this range were achieved in 72% of patients when doses of 10--14 mg-1 kg-1 day were given orally.

Long-term oral antiarrhythmic therapy with mexiletine

Forty-eight patients with ischaemic heart disease received oral mexiletine for the control or prevention of ventricular arrhythmias. The most frequently used doses were 200, 250, and 300 mg 8-hourly. The treatment period varied from 2 days to more than 1 year (median 3 months). No ventricular arrhythmias were detected in more than one-half of the patients. Severe side effects occurred in 15 (31%) of the 48 patients. Major ventricular arrhythmias were observed in 14 (29%) of the 48 patients at a time when the majority had plasma concentrations within the therapeutic range. The value of mexiletine in the management of patients at risk of sudden death is likely to be limited.

Efficacy of oral mexiletine in the prevention of exercise-induced ventricular ectopic activity

The anti-arrhythmic effect of oral mexiletine on exercise-induced ventricular arrhythmia was studied in a double blind trial of 10 patients suffering from ventricular ectopic beats of different origins. There was a good reproducibility of the amount of ectopic ventricular activity between consecutive exercise tests when no active drug was given. Treatment for 1 week with mexiletine 600 mg daily resulted in a statistically significant reduction in ventricular ectopic beats, particularly during and after exercise; there were virtually no side-effects. The results suggest that mexiletine has considerable potential in the treatment of ventricular arrhythmias.

New antiarrhythmic agents: amiodarone, aprindine, disopyramide, ethmozin, mexiletine, tocainide, verapamil

The present status, clinical experience, side effects, clinical pharmacology and electrophysiologic actions of seven new antiarrhythmic agents are reviewed. The drugs selected for comment are amiodarone, aprindine, disopyramide, ethmozin, mexiletine, tocainide and verapamil. Each drug has been shown to have clinical efficacy in suppressing cardiac arrhythmias.