The antiarrhythmic efficacy of
mexiletine in acute
myocardial infarction (AMI) was studied in 99 patients randomized to
mexiletine or placebo treatment. The loading dose was 250 mg i.v. and 400 mg orally followed by 200 mg orally 2 h later, and thereafter 200 mg t.i.d. up to 42 h. Arrhythmias occurring during 48 h were analysed from continuous electrocardiographic recordings. AMI was verified in 35 of 50
mexiletine patients and in 38 of 49 placebo patients. No deaths or instances of
ventricular fibrillation occurred in the AMI patients. The number of patients who had any event of
accelerated idioventricular rhythm (
AIVR; P less than 0.05) runs of ventricular
premature beats (VPBs; P less than 0.01),
ventricular tachycardia (P less than 0.01) and Ron T beats (P less than 0.05) was smaller in the
mexiletine group than in the placebo group. The number of all VPBs (P less than 0.05), hours with occurrence of
AIVR (P less than 0.05), runs (P less than 0.01) and Ron T beats (P less than 0.05) was smaller in the
mexiletine than in the placebo group. Serum levels of
mexiletine tended to be low throughout the study. The half-life of the elimination was 13.7 +/- 7.2 h (means +/- S.D.). Adverse effects were infrequent, and the treatment was well-tolerated. Combined iv. and oral
mexiletine prophylaxis significantly suppressed repetitive
ventricular tachyarrhythmias and Ron T beats. However, no clinical benefit from
mexiletine treatment could be shown in a coronary care unit with a low frequency of primary
ventricular fibrillation.