A medication order reads 0.75 mg. If the vial contains 0.25 mg/mL, how many milliliters should be administered?

• A. 3 mL
• B. 1.5 mL
• C. 0.75 mL
• D. 2 mL

Answer: (A)

When you have a dose in mg and a solution concentration in mg per mL, use volume = dose ÷ concentration. Here the dose is 0.75 mg and the concentration is 0.25 mg/mL, so 0.75 ÷ 0.25 = 3. This means you should administer 3 mL.

This makes sense because 1 mL contains 0.25 mg; three such milliliters contain 0.25 mg × 3 = 0.75 mg. So anything smaller would deliver less than the prescribed dose (for example, 1.5 mL gives 0.375 mg, 0.75 mL gives 0.1875 mg, and 2 mL gives 0.5 mg).