Procainamide and phenytoin Comparative study of their antiarrhythmic effects at apparent therapeutic plasma levels

Abstract

The antiarrhythmic effects ofprocainamide andphenytoin were studied in 8i patients admitted to the coronary care unit at the University Hospital in Linkeping because ofa suspected orproven diagnosis ofacute myocardial infarction, and who developed ventricular arrhythmias, requiring treatment, during the first 8 hours in hospital. Patients were randomly allocated to a procainamide or phenytoin group. The drugs were given as intravenous and oral loading dosesfollowed by oral maintenance therapy. Plasma levels of the two drugs were frequently determined and the electrocardiogram was continuously recorded during the 24-hour trial and analysed minute by minute. A significantly higher frequeng of therapeutic failure was found in the phenytoin group (23 of 35 patients) compared to the procainamide group (13 of 39 patients) during thefirst 2 hours after initiation of therapy. Four patients in the phenytoin group and 2 in the procainamide group developed symptoms probably caused by the trial drugs, necessitating discontinuation of therapy. The mean plasma levels were usually within the apparent therapeutic range (for phenytoin 40-72 pLmol/l (IO-8 μg/ml), and for procainanmde I7-34 μmol/l (4-8 μmi). Seventeen patients (68%) in the phenytoingroup and io patients (48%) in the procainamide group had plasma concentrations within this range when the therapeutic failure was observed. Nine patients died in hospital but only one of them during the trial. The results of this investigation clearly demonstrate the overall superiority of procainamide over phenytoin as an antiarrhythmic drug in short-term therapy after acute myocardial infarction.