What is the typical therapeutic serum level range for digoxin?

• A. 0.1-0.3 ng/mL
• B. 5-10 ng/mL
• C. 0.5-2 ng/mL
• D. 10-20 ng/mL

Answer: (C)

Digoxin has a very narrow therapeutic index, so its serum level must stay within a small window to provide benefit without causing toxicity. The typical therapeutic range is 0.5–2 ng/mL. Within this range, the drug can improve symptoms and rate control in heart conditions without pronounced toxicity for most adults. Levels below this range are unlikely to help, while levels well above it markedly raise the risk of toxicity, which can manifest as GI upset, confusion, vision changes, and slow or irregular heart rhythms. When checking digoxin, measure a trough level just before the next dose (usually 6–8 hours after a dose) to gauge the minimum concentration. Dose adjustments should also consider kidney function and potential drug interactions.