Digoxin (lavoxin) 0.125 mg is ordered. It is available in a dose vial 500 mcg/mL. How many mL does the nurse administer?

Appeared in: NVS- 2025

Explanation

The first step is to ensure the units of the ordered dose and the available dose are the same. The ordered dose of 0.125 mg is converted to 125 mcg (0.125 x 1000).
The standard formula for dosage calculation is (Desired Dose / Dose on Hand) × Quantity.
Plugging in the values: The desired dose is 125 mcg, the dose on hand is 500 mcg, and the quantity is 1 mL.
The final calculation is (125 mcg / 500 mcg) × 1 mL, which equals 0.25 mL.

Option B: This value is incorrect. A calculation error, such as misplacing the decimal or using incorrect values, would lead to this result.
Option C: This result is incorrect. It would be the correct answer only if the available concentration was 50 mcg/mL (or 500 mcg/10 mL), not 500 mcg/mL as stated in the problem.
Option D: This value is incorrect. It is likely the result of a significant miscalculation, possibly by inverting the fraction (500/125) and then dividing by two.

Clinical Relevance

Nursing practice connection: Knowing Medication Dosage Calculation helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
Accurate medication calculation is a critical nursing skill to prevent dosing errors, which can lead to adverse drug events or toxicity.
Digoxin has a narrow therapeutic index, meaning small differences in dose can lead to serious toxicity. Double-checking calculations is a crucial patient safety measure.
If a calculation results in an answer that does not match any of the options, or seems unusual, the nurse has a professional responsibility to stop, re-verify the order and the calculation, and consult with a pharmacist or the prescribing provider before administering.

How to Approach the Question

First, identify all the given information: the desired dose (0.125 mg), the dose on hand (500 mcg), and the quantity it comes in (1 mL).
Next, check if the units for the desired dose and the dose on hand are the same. Here, they are different (mg and mcg).
Convert one of the units to match the other. It is usually easiest to convert the larger unit to the smaller unit (mg to mcg) to avoid decimals.
Apply the 'Desired over Have times Quantity' formula: (D/H) x Q.
Perform the calculation carefully: (125 mcg / 500 mcg) x 1 mL.
Select the option that matches your calculated result. If no option matches, re-check your math and the problem's values.

Concept Tested & Keywords

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E6 Nursing Fundamentals Taylor pp. 922-924, 848-850

E6 Pharmacology Katzung 16e p. 89-91

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