Using a concentration of 15 mg per mL, how many milliliters are required to administer a 45 mg dose?

Using a concentration of 15 mg per mL, how many milliliters are required to administer a 45 mg dose?

• A. 1.5 mL
• B. 3 mL
• C. 0.5 mL
• D. 6 mL

Answer: (B)

Understanding how to convert a prescribed dose into the volume to administer relies on the fact that concentration tells you how much drug is in each milliliter. To find the volume, divide the desired dose by the concentration: Volume = Dose / Concentration. Here, the dose is 45 mg and the concentration is 15 mg per mL. 45 mg ÷ 15 mg/mL = 3 mL. That means you need 3 mL to deliver 45 mg. A quick check: 3 mL × 15 mg/mL = 45 mg, which matches the prescribed dose. If you gave less or more volume, you'd get a smaller or larger dose: for example, 1.5 mL would give 22.5 mg, 0.5 mL would give 7.5 mg, and 6 mL would give 90 mg.

Understanding how to convert a prescribed dose into the volume to administer relies on the fact that concentration tells you how much drug is in each milliliter. To find the volume, divide the desired dose by the concentration: Volume = Dose / Concentration. Here, the dose is 45 mg and the concentration is 15 mg per mL. 45 mg ÷ 15 mg/mL = 3 mL. That means you need 3 mL to deliver 45 mg. A quick check: 3 mL × 15 mg/mL = 45 mg, which matches the prescribed dose. If you gave less or more volume, you'd get a smaller or larger dose: for example, 1.5 mL would give 22.5 mg, 0.5 mL would give 7.5 mg, and 6 mL would give 90 mg.