Digoxin Dosing Calculator

The Digoxin Dosing Calculator estimates loading and maintenance doses of digoxin using pharmacokinetic principles based on patient weight, renal function, and clinical indication. Digoxin is a cardiac glycoside that has been used for over 200 years, derived from the foxglove plant (Digitalis purpurea), and remains clinically relevant for atrial fibrillation rate control and heart failure management despite the availability of newer agents.

Digoxin exerts its therapeutic effects through inhibition of the sodium-potassium ATPase pump in cardiac myocytes, leading to increased intracellular calcium and enhanced cardiac contractility (positive inotropic effect). At lower doses, its primary benefit is neurohormonal modulation, reducing sympathetic activation and enhancing vagal tone. In atrial fibrillation, digoxin slows ventricular rate by increasing the refractory period of the AV node through vagal enhancement.

The pharmacokinetics of digoxin are complex and clinically important. It has a large volume of distribution (approximately 5-7 L/kg in lean tissue) due to extensive tissue binding. Renal elimination accounts for 60-80% of clearance, making dose adjustment for renal function essential. The half-life ranges from 36-48 hours with normal renal function, extending to 3.5-5 days in severe renal impairment. This long half-life means that steady state is not achieved for 5-7 days after initiation or dose changes.

Current guidelines recommend lower serum digoxin concentrations than historically targeted. For heart failure (HFrEF), the DIG trial and subsequent analyses suggest maintaining levels of 0.5-0.9 ng/mL for mortality benefit, with levels >1.0 ng/mL associated with increased mortality. For atrial fibrillation rate control, levels of 0.8-2.0 ng/mL may be appropriate, though lower targets are increasingly favored. The narrow therapeutic index of digoxin (therapeutic range 0.5-2.0 ng/mL, toxicity common >2.0 ng/mL) necessitates careful dose individualization.

Loading doses (digitalization) may be used when rapid therapeutic levels are needed, particularly for atrial fibrillation with rapid ventricular response. The oral loading dose is typically administered in divided doses (half initially, then quarter doses at 6-8 hour intervals) to allow assessment of response and minimize toxicity. For non-urgent situations, starting with the maintenance dose alone achieves steady state in approximately 5 half-lives (7-10 days with normal renal function).

This calculator uses the Jusko-Koup method to estimate volume of distribution based on lean body weight and creatinine clearance, then calculates both loading and maintenance doses rounded to available tablet strengths (62.5 mcg increments: 62.5, 125, 187.5, 250 mcg). Oral bioavailability of digoxin tablets is assumed at 70% (compared to 100% for IV and 90% for elixir).

Digoxin toxicity is a serious concern, with manifestations including cardiac arrhythmias (any type, but characteristically atrial tachycardia with block or bidirectional VT), GI symptoms (nausea, vomiting, anorexia), and visual disturbances (yellow-green halos, blurred vision). Hypokalemia, hypomagnesemia, and hypothyroidism increase sensitivity to digoxin toxicity. Digoxin-specific antibody fragments (Digibind/DigiFab) provide definitive treatment for severe toxicity.

This calculator provides pharmacokinetically guided dosing to support safe and effective digoxin therapy in clinical practice.