Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
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.
Monitoring propafenone therapy
The therapeutic concentration is 0.5 to 2.0 mcg/mL; concentrations <0.5 mcg/mL likely indicate inadequate therapy and propafenone >2.0 mcg/mL indicates excessive therapy.
Toxic concentration: >2.0 mcg/mL
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
No significant cautionary statements
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
Therapeutic concentration: 0.5-2.0 mcg/mL
Clinical References Provides recommendations for further in-depth reading of a clinical nature
1. Burtis CA, Ashwood ER, Bruns DE: Tietz Textbook of Clinical Chemistry and Molecular Diagnosis. Fifth edition. Elsevier, St. Louis, USA, 2012
2. Antman EM, Beamer AD, Cantillon C, et al: Long-term oral propafenone therapy for suppression of refractory symptomatic atrial fibrillation and atrial flutter. J Am Coll Cardiol 1988;12:1005-1011