Clinical Information

Tocainide, mexiletine, flecainide, and propafenone are all class I antiarrhythmic agents whose dominant cardiac effect is to reduce the rate of rise of the action potential in cardiac cells. In so doing, they increase the threshold of excitability of myocardial cells, depress the conduction velocity of the impulse around the heart, and prolong the defective refractory period, which results in stabilization of the heart rate. All 4 drugs are effective following oral administration.

Tocainide, mexiletine, and flecainide undergo minimal first-pass metabolism and have relatively long half-lives (10-16 hours). In contrast, propafenone undergoes extensive first-pass metabolism (half-life is approximately 1-3 hours). Its clinical efficacy is maintained through the formation of a metabolite (5-hydroxypropafenone) that is more pharmacologically active than the parent drug and has a longer plasma half-life (6-12 hours).

Propafenone is primarily used to treat ventricular arrhythmias (ventricular tachycardia, supraventricular tachycardia, and ventricular premature contractions).

Specimens should only be drawn after patient has been receiving propafenone orally for at least 3 days. Trough concentrations should be drawn just before administration of the next dose.

Adverse side effects are seen in the central nervous system, skin, and gastrointestinal tract.