Digoxin Dosing Calculator
Calculate digoxin loading and maintenance doses from weight, renal function, and lean body mass.
Reviewed by Rahul Singh, Health & Wellness Specialist
Formula
Vd = (226 + 298 x CrCl/(29.1 + CrCl)) x LBM/70 | Loading = Css x Vd | Maintenance = TBS x Daily Loss%
Volume of distribution (Vd) is calculated using the Jusko-Koup equation adjusted for lean body mass. Total body stores (TBS) equal the desired concentration times Vd. Loading dose equals TBS adjusted for bioavailability (70% oral, 100% IV). Maintenance dose replaces the daily elimination fraction. Creatinine clearance is estimated via Cockcroft-Gault.
Worked Examples
Example 1: Atrial Fibrillation Rate Control Dosing
Problem:A 65-year-old male (70 kg, 170 cm) with atrial fibrillation needs digoxin for rate control. Serum creatinine: 1.2 mg/dL. Target level: 1.0 ng/mL.
Solution:LBM (male) = 50 + 2.3 x ((170/2.54) - 60) = 50 + 2.3 x 6.93 = 65.9 kg\nCrCl = ((140-65) x 70) / (72 x 1.2) = 5250/86.4 = 60.8 mL/min\nVd = (226 + 298 x 60.8/(29.1+60.8)) x 65.9/70 = (226 + 201.5) x 0.941 = 402.5 L\nTBS = 1.0 x 402.5 = 402.5 mcg\nLoading IV = 0.403 mg (give 0.2 mg, then 0.1 mg x2)\nDaily Loss = ~25%\nMaintenance oral = ~0.18 mg/day\nNearest tablet: 0.1875 mg (3/4 of 0.25 mg tab)
Result:Loading: 0.4 mg IV divided | Maintenance: 0.1875 mg oral daily | Predicted SS: ~1.0 ng/mL
Example 2: Heart Failure Patient with Renal Impairment
Problem:A 78-year-old female (55 kg, 157 cm) with heart failure. Serum creatinine: 1.8 mg/dL. Target level: 0.7 ng/mL.
Solution:LBM (female) = 45.5 + 2.3 x ((157/2.54) - 60) = 45.5 + 2.3 x 1.8 = 49.6 kg\nCrCl = ((140-78) x 55) / (72 x 1.8) x 0.85 = 3410/129.6 x 0.85 = 22.4 mL/min\nVd = (226 + 298 x 22.4/(29.1+22.4)) x 49.6/70 = (226 + 129.6) x 0.709 = 252.0 L\nTBS = 0.7 x 252.0 = 176.4 mcg\nLoading IV = 0.176 mg\nReduced CrCl means slower elimination: ~15% daily loss\nMaintenance = 0.176 x 0.15 / 0.7 = 0.038 mg oral = 0.0625 mg every other day
Result:Loading: 0.175 mg IV divided | Maintenance: 0.0625 mg oral every other day | Monitor levels closely
Frequently Asked Questions
How is the digoxin loading dose calculated from patient parameters?
The digoxin loading dose is calculated by first determining the volume of distribution, which depends on lean body mass and renal function. The volume of distribution in liters is estimated using the Jusko-Koup equation: Vd = (226 + 298 x CrCl / (29.1 + CrCl)) adjusted for lean body mass. The total body stores needed are then calculated by multiplying the desired serum concentration in nanograms per milliliter by the volume of distribution in liters. For IV administration, the loading dose equals the total body stores since bioavailability is 100 percent. For oral tablets, the dose is divided by 0.7 to account for 70 percent bioavailability. The loading dose is typically administered in divided doses: half the total dose initially, then one quarter at 6 to 8 hours, and the final quarter at 6 to 8 hours later, to reduce the risk of toxicity from rapid administration.
Why is lean body mass used instead of total body weight for digoxin dosing?
Digoxin is highly lipophobic and distributes primarily into lean tissue, skeletal muscle, and organs rather than adipose tissue. Using total body weight in obese patients would overestimate the volume of distribution and result in supratherapeutic doses that increase toxicity risk. Lean body mass provides a more accurate estimate of the tissue compartment where digoxin actually distributes. The Devine formula is commonly used to estimate lean body mass: for males it equals 50 kg plus 2.3 kg per inch over 5 feet, and for females it equals 45.5 kg plus 2.3 kg per inch over 5 feet. In significantly obese patients where total body weight exceeds 120 percent of ideal body weight, an adjusted body weight using 40 percent of the excess weight is used for creatinine clearance estimation while lean body mass is used for volume of distribution calculations.
What is the therapeutic range for digoxin and why does it differ by indication?
The therapeutic range for digoxin varies based on the clinical indication. For heart failure, the DIG trial and subsequent analyses demonstrated that serum digoxin concentrations of 0.5 to 0.9 ng/mL provide optimal benefit with reduced mortality, while levels above 1.0 ng/mL were associated with increased mortality despite symptom improvement. For atrial fibrillation rate control, higher levels between 0.8 and 2.0 ng/mL may be needed to achieve adequate ventricular rate reduction, though current guidelines recommend targeting the lower end of this range. The narrow therapeutic index of digoxin means that the toxic concentration of approximately 2.0 ng/mL is only about twice the lower therapeutic level. This narrow margin makes careful dosing, monitoring, and awareness of drug interactions and electrolyte abnormalities essential for safe digoxin use.
How does renal function affect digoxin dosing and elimination?
Renal function is the single most important determinant of digoxin maintenance dosing because approximately 60 to 80 percent of digoxin is eliminated unchanged by the kidneys through glomerular filtration and tubular secretion. The remaining 20 to 40 percent undergoes hepatic metabolism and biliary excretion. In patients with reduced creatinine clearance, digoxin elimination is significantly prolonged, leading to accumulation and potential toxicity if doses are not reduced. For a patient with normal renal function and a creatinine clearance of 100 mL/min, the digoxin half-life is approximately 36 to 48 hours. In a patient with severe renal impairment and creatinine clearance of 20 mL/min, the half-life may extend to 4 to 6 days. Digoxin Dosing Calculator uses the Cockcroft-Gault equation to estimate creatinine clearance and adjusts both the volume of distribution and daily maintenance dose accordingly.
References
Reviewed by Rahul Singh, Health & Wellness Specialist · Editorial policy