What is the therapeutic serum range for digoxin and what monitoring parameter guides dosing?

• A. Serum digoxin typically 0.5–2.0 ng/mL; monitor renal function and potassium; adjust as needed.
• B. Serum digoxin typically 5–10 ng/mL; monitor calcium.
• C. Serum digoxin typically 0.05–0.2 ng/mL; monitor liver enzymes.
• D. Serum digoxin typically 2–5 ng/mL; monitor hemoglobin.

Answer: (A)

Digoxin has a narrow therapeutic window, so the dose must be adjusted to keep levels in a safe range while avoiding toxicity. For most adults, the therapeutic serum range is about 0.5 to 2.0 ng/mL. Dosing is guided primarily by renal function because the drug is cleared by the kidneys; reduced kidney function slows clearance and can lead to accumulation, necessitating dose adjustments. Potassium status is also crucial because digoxin binds to the Na+/K+-ATPase; hypokalemia increases digoxin binding and toxicity risk, while normal or higher potassium helps mitigate that risk. Therefore, monitoring renal function and potassium levels helps tailor the dose to stay within the safe range. The other ranges listed are outside the therapeutic window or the monitoring parameter isn’t the one used to guide digoxin dosing (calcium, liver enzymes, or hemoglobin).