Mexiletine in acute myocardial infarction. Simulation of a theoretical protocol and validation in six patients

A mexiletine (Mexitil, MEX) administration schedule was established by simulation, in order to maintain MEX at therapeutic levels in plasma during the transition from parenteral to slow-release MEX (SR MEX) administration. This protocol was made valid in 6 patients with acute myocardial infarction (AMI) admitted to a coronary care unit, 24 h after the onset of pain. From both the i.v. and oral plasma level data, the pharmacokinetic parameter alterations of MEX and its hydroxymethylmexiletine metabolite (OH MEX) were evaluated over a week's period. The results presented here demonstrate that a twice daily oral SR MEX administration, starting at the end of MEX infusion, maintains the therapeutic concentrations of MEX (750-2000 ng/ml) previously achieved by infusion therapy (at 48 h, end of infusion, mean +/- SD = 1393 +/- 325 ng/ml; at 60 h, mean +/- SD = 1434 +/- 376 ng/ml; at 96 h, mean +/- SD = 1423 +/- 367 ng/ml. No evidence of either clinical side-effects or malignant arrhythmias was observed. MEX and OH MEX pharmacokinetic parameters were estimated by fitting the i.v. infusion data (phase I) and the oral data after the last SR MEX administration (phase II)beta to a linear compartment model. The terminal half-life t1/2 MEX was longer in phase I than in phase II (28.4 +/- 12.1 h (betaI) versus 14.06 +/- 4.47 h (II); p less than 0.01). This prolonged t1/2 MEX was probably due to a decrease of total plasma clearance Cl MEX (3.723 +/- 1.534 ml.kg-1min-1 (I) versus 5.031 +/- 1.28 ml.kg-1min-1 (II).(ABSTRACT TRUNCATED AT 250 WORDS)