A drug is supplied as 8 mg/mL. The order is 32 mg. How many milliliters should be administered?

• A. 2 mL
• B. 4 mL
• C. 6 mL
• D. 8 mL

Answer: (B)

You determine the volume to give by dividing the ordered dose by the drug’s concentration, because the concentration tells you how many milligrams are in each milliliter.

With a concentration of 8 mg per 1 mL, the required volume is 32 mg ÷ 8 mg/mL = 4 mL. You can verify this by back-calculating: 4 mL × 8 mg/mL = 32 mg, which matches the order.

The other amounts would deliver different total milligrams: 2 mL would be 16 mg, 6 mL would be 48 mg, and 8 mL would be 64 mg, so they don’t meet the prescribed dose.