Digitalis is a class of medicines derived from the foxglove plant (Digitalis purpurea and Digitalis lanata) that have been used in medicine for over 200 years. The active compounds, primarily digoxin and digitoxin, have positive inotropic effects (strengthening the force of heart muscle contraction) and negative chronotropic effects (slowing the heart rate). The most commonly used preparation today is digoxin.
Digitalis medicines act by inhibiting the sodium-potassium ATPase pump in heart muscle cells, increasing intracellular sodium and, indirectly, intracellular calcium. The increased calcium availability enhances the strength of each heartbeat. Digoxin also slows conduction through the atrioventricular (AV) node, making it useful for controlling ventricular rate in atrial fibrillation.
The clinical uses of digoxin have narrowed considerably as more effective drugs have become available. It is used mainly for rate control in atrial fibrillation (particularly in patients with concurrent heart failure) and occasionally as an add-on treatment for heart failure with reduced ejection fraction when other first-line agents are insufficient.
Digitalis has a narrow therapeutic index: the dose required for benefit is close to the dose that causes toxicity. Digoxin toxicity can cause nausea, vomiting, visual disturbances (including characteristic yellow-green halos), and dangerous arrhythmias including heart block and ventricular tachycardia. Toxicity is worsened by low potassium and magnesium levels, which are common in patients taking diuretics. Regular monitoring of serum digoxin levels, potassium, and renal function is required for patients on long-term treatment.
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