Digoxin Dosing Calculator

Digoxin is a cardiac glycoside used primarily for rate control in atrial fibrillation and as a positive inotrope in heart failure with reduced ejection fraction. Because digoxin distributes extensively into lean tissue — particularly skeletal muscle — its volume of distribution is calculated using lean body weight (LBW) rather than total body weight. The Devine formula is used to estimate LBW: 50 kg + 2.3 kg per inch over 5 feet for males, and 45.5 kg + 2.3 kg per inch over 5 feet for females. If total body weight is less than LBW, total body weight is used instead.

The volume of distribution is approximated as 7.3 L/kg of LBW. Renal function drives digoxin elimination — roughly 60–80% of digoxin is excreted unchanged by the kidneys. Creatinine clearance is estimated using the Cockcroft-Gault equation. The elimination rate constant (ke) is calculated as ke = 0.02 + (0.88 × CrCl/100), reflecting both renal and non-renal clearance. The loading dose represents the amount needed to rapidly fill the volume of distribution to the target concentration, corrected for bioavailability (approximately 70% for oral tablets, 100% for IV). The maintenance dose replaces the drug eliminated each day at steady state.

Target serum digoxin concentrations vary by indication: 0.5–0.9 ng/mL is recommended for heart failure (low-concentration strategy shown to reduce mortality), while 0.8–2.0 ng/mL may be used for rate control in atrial fibrillation. Digoxin levels above 2.0 ng/mL are associated with significantly increased toxicity risk including nausea, visual disturbances, and life-threatening arrhythmias. Clinicians should always verify calculated doses against institutional protocols and use therapeutic drug monitoring (TDM) to guide therapy.

This calculator provides pharmacokinetic estimates only and should never replace clinical judgment, institutional dosing protocols, or therapeutic drug monitoring. The Cockcroft-Gault creatinine clearance equation assumes stable renal function — it is unreliable in acute kidney injury, rapidly changing renal function, extreme body compositions, or patients with very low muscle mass (e.g., elderly, malnourished, or paraplegic patients). The volume of distribution constant of 7.3 L/kg is a population average and can vary substantially in patients with severe heart failure, hypothyroidism, hyperthyroidism, or significant fluid shifts — all conditions that alter digoxin distribution. Hypothyroidism reduces Vd and clearance (requiring lower doses), while hyperthyroidism increases clearance (requiring higher doses). Digoxin has numerous clinically significant drug interactions — notably with amiodarone, quinidine, spironolactone, verapamil, and P-glycoprotein inhibitors — which can raise serum digoxin levels by 50–100% and require empiric dose reduction. Obesity significantly complicates dosing; obese patients should be dosed on LBW, not total body weight, as digoxin does not distribute appreciably into adipose tissue. Pediatric and neonatal dosing follows entirely different weight-based protocols not covered by this calculator. Serum digoxin levels should be drawn at least 6–8 hours after the last dose to avoid the distribution phase, which can falsely elevate measured concentrations. Always confirm all calculated doses with a clinical pharmacist before prescribing.