**Question:** Therapeutic plasma level of digoxin is:

A. 0.5-2 ng/mL
B. 0.5-3 ng/mL
C. 0.5-2.0 ng/mL
D. 0.5-3.5 ng/mL

**Core Concept:** Digoxin is a cardiac glycoside used to treat heart failure and atrial fibrillation. It works by increasing the contractility of cardiac muscle cells and reducing the heart rate. Therapeutic plasma levels are crucial for effective treatment and minimizing side effects.

**Why the Correct Answer is Right:** The correct answer is 0.5-2 ng/mL. Therapeutic digoxin levels are essential for optimal treatment outcomes. A therapeutic level ensures that the drug is effective in treating the intended condition without causing significant adverse effects due to toxicity.

**Why Each Wrong Option is Incorrect:**

A. 0.5-3 ng/mL: This answer is close but misses the optimal range by being too high. The therapeutic range is crucial for efficient treatment and minimizing side effects.

B. 0.5-3 ng/mL: This option provides the correct range but with a slightly higher lower limit. Still, it is near the optimal range, so this answer can be considered close but wrong.

C. 0.5-2.0 ng/mL: This option uses a slightly different notation (ng/mL vs. ng/dL) but maintains the same therapeutic range. However, the lower limit is too high, making it incorrect.

D. 0.5-3.5 ng/mL: This answer is too high, as it extends beyond the optimal therapeutic range for digoxin levels, which can lead to toxicity and adverse effects.

**Clinical Pearl:** Digoxin toxicity can present with various symptoms, including gastrointestinal complaints, confusion, and a slowed heart rate. Monitoring therapeutic digoxin levels is essential for safe and effective treatment.

**Correct Answer:** C. 0.5-2.0 ng/mL

**Core Concept:** Digoxin is a cardiac glycoside that regulates the heart rate and contractility, and its therapeutic level depends on the patient's weight and renal function. Ensuring the correct therapeutic level ensures optimal treatment and minimizes the risk of toxicity.

**Why the Correct Answer is Right:** The correct range (0.5-2.0 ng/mL) is suitable for most patients. However, it is crucial to adjust the therapeutic level based on the patient's body weight and renal function since digoxin excretion is dependent on renal function.

**Why Each Wrong Option is Incorrect:**

A. 0.5-3.0 ng/mL: This answer is too low, increasing the risk of therapeutic inefficacy and potentially worsening the condition being treated.

B. 0.5-3.5 ng/mL: This answer is too high, increasing the risk of toxicity and adverse effects.

C. 0.5-2.0 ng/mL: This answer is within the optimal range and is the correct choice.

D.