Flecainide and encainide

Flecainide and encainide (class IC) are presently under clinical evaluation in Italy. They prolong the duration of the QRS but not the period of ventricular repolarisation: the prolongation of QT is due solely to the prolongation of the Q-J. Flecainide and encainide are extremely powerful and are suitable for the treatment of reciprocating supraventricular paroxysmal tachycardia and of persistent reciprocating tachycardia, the prophylaxis of WPW atrial fibrillation including cases with a short anterograde refractory period of the anomalous pathway and the treatment of ventricular ectopic beats and ventricular tachycardia. Both drugs are probably effective for the treatment of atrial fibrillation. However, in the case of atrial flutter they are of little effect for sinus rhythm cardioversion; on the other hand they significantly prolong the duration of the A-A interval, with variable results on ventricular rate. Flecainide and encainide have ‘parodoxical’ arrhythmogenic effects, related to administration dosages, severity of the arrhythmia and seriousness of cardiopathy. Encainide shows peculiar pharmacokinetics due to hepatic oxidating metabolisation and to production of metabolites; among these the O-demethylencainide and the 3-methoxy-O-demethylencainide have an antiarrhythmic activity, which is probably more important than the encainide parent and is longer-lasting. There are ‘extensive’, ‘poor’ and ‘non-metaboliser’ subjects. This results in wide pharmacokinetic inter- and intraindividual variability which must be taken into account during clinical treatment. Although flecainide and encainide have only been introduced recently into clinical practice, they have a vast experimental and clinical bibliography. Papers include extensive studies on the pharmacological and pharmacokinetic characteristics, the electrophysiologic and haemodynamic effects, clinical information and the side-effects. This brief presentation will emphasise the advantages which the drugs can offer in the clinical treatment of arrhythmias.