The absorption of oral mexiletine in coronary care patients

In a preliminary study of mexiletine absorption in Coronary Care Unit patients with myocardial infarction, plasma mexiletine concentrations were significantly lower in those given narcotic analgesics. 166 patients then entered a comparative study of the effects of mexiletine and placebo on the incidence of ventricular arrhythmias after myocardial infarction (MI). Eighty-two patients were given mexiletine, 51 with MI. Mexiletine absorption was impaired in patients with MI and 66% failed to reach the minimum therapeutic plasma concentration of 1 μg/ml in 3 h. On the second and third hospital days, 34% and 25% respectively had subtherapeutic levels. In patients without MI, low plasma mexiletine concentrations were associated with the use of narcotic analgesics. The incidence of serious ventricular arrhythmias (VF, VT, R on T ectopic beats) was significantly lower in patients given mexiletine, and after 3 h most arrhythmias in this group occurred in patients with subtherapeutic mexiletine concentrations. Therapeutic failure of oral antiarrhythmic drugs soon after MI may be due to impaired absorption.