Hemodynamic effects of mexiletine were studied in 15 patients with normal sinus rhythm; most of them had a myocardial infarction. Except for a slight increase in peripheral vascular resistance, no other significant change in hemodynamic parameters was found after an intravenous injection of 1.5 mg/kg of mexiletine at 25 mg/min.
Mexiletine (Mexitil) is an effective antiarrhythmic drug for the treatment of ventricular dysrhythmias. The therapeutic plasma level is situated between 0.75 and 2 microgram/ml. For concentrations higher than 2 microgram/ml, the percentage of severe side effects is rapidly increasing without improvement of the therapeutic efficacy. The main pharmacokinetics parameters of mexiletine are reviewed in the first part of this publication. Contrary to lidocaine, mexiletine may be administrated orally (or intravenously). It is largely and rapidly distributed in the body. The apparent volume of distribution (Vd) is greater than 500 1. The plasma half-time is 10 to 12 hours in healthy volunteers with a 70% plasma protein fixation. Mexiletine is largely metabolized to conjugates after N-methylation and hydroxylation. In the second part of the work, the influence of renal insufficiency on the plasma half-time of mexiletine has been investigated in 11 patients presenting a creatinine clearance situated between 2 and 38 ml/min. The mean plasma half-time for these patients is 11.1 +/- 1.7 hours after a single i.v. injection of 1.5 mg/kg. This value is comparable to the normal values found in the literature. Our control group containing convalescents from acute myocardial infarct has a plasma half-time of only 5.9 hours. In conclusion, the renal insufficiency has not modified the plasma elimination half-time of mexiletine after a single i.v. injection.
For the evaluation of arrhythmias and the assessment of antiarrhythmic therapy prolonged periods of recording, as provided by the Holter system, are needed. The 12 lead electrocardiogram and rhythm strips are unsuitable for these purposes. However an exercise test may provide useful additional information. In two trials mexiletine was compared with other antiarrhythmic drugs (atenolol, disopyramide, lorcainide) and placebo. In both trials mexiletine was shown to have a good antiarrhythmic efficacy on chronic ventricular premature beats. The high incidence of side-effects was probably due to the high dosage used.
Mexilitine is an antiarrhythmic drug with pharmacological properties similar to lignocaine. It is effective against ventricular arrhythmias, both parenterally and orally, and has been used in acute myocardial infarction, in the convalescence following myocardial infarction and in ventricular arrhythmias of different aetiology. The incidence of serious side-effects is sufficiently low to warrant its use.
The effect of mexiletine, a new antiarrhythmic drug, was studied by oral (600 to 1200 mg/day) or intravenous (250 mg in 10 minutes) route in 45 patients; most of them had coronary insufficiency. Our results show that mexiletine is a potent ventricular antiarrhythmic drug which is efficient on several types of xylocaine resistant ventricular arrhythmias. In our experience, mexiletine is reliable when administered intravenously; there are frequent and sometimes severe side-effects when given orally.
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