What is the therapeutic plasma range for Digoxin?

• A. 2-3.5 ng/mL
• B. 0.1-2 ng/mL
• C. 0.5-2 ng/mL
• D. 3.5-5 ng/mL

Answer: (C)

Digoxin has a narrow therapeutic index, so the goal is to keep its plasma level within a window that provides benefit without toxicity. For adults, the therapeutic range is 0.5 to 2 ng/mL. Within this range, digoxin can improve cardiac contractility and help control ventricular rate without causing serious adverse effects. Levels below 0.5 ng/mL may be subtherapeutic and less effective, while levels above about 2 ng/mL markedly increase the risk of toxicity, which can include GI symptoms, vision changes, bradycardia, and dangerous arrhythmias. The other proposed ranges either fall outside this safe window or are clearly toxic, reinforcing why 0.5–2 ng/mL is the best target. Remember to consider kidney function and electrolyte balance, since renal impairment or hypokalemia can raise toxicity risk even within the therapeutic range.