A nurse needs to administer 125 mg of a medication. The vial concentration is 250 mg/mL. How many milliliters should be drawn?

A nurse needs to administer 125 mg of a medication. The vial concentration is 250 mg/mL. How many milliliters should be drawn?

• A. 0.25 mL
• B. 0.5 mL
• C. 1.0 mL
• D. 2.0 mL

Answer: (B)

The key idea is converting a drug dose into the volume to draw using the vial’s concentration. Use volume = dose ÷ concentration. Here, dose is 125 mg and the concentration is 250 mg per 1 mL. 125 ÷ 250 equals 0.5, so you should draw 0.5 mL. This makes sense because the desired dose is half of what’s in one milliliter, so half a milliliter is required. Always check units: mg cancels, leaving mL. You can also see it by cross-multiplying: 125 mg × 1 mL ÷ 250 mg = 0.5 mL.

The key idea is converting a drug dose into the volume to draw using the vial’s concentration. Use volume = dose ÷ concentration. Here, dose is 125 mg and the concentration is 250 mg per 1 mL. 125 ÷ 250 equals 0.5, so you should draw 0.5 mL. This makes sense because the desired dose is half of what’s in one milliliter, so half a milliliter is required. Always check units: mg cancels, leaving mL. You can also see it by cross-multiplying: 125 mg × 1 mL ÷ 250 mg = 0.5 mL.