If a vial contains 125 mg in 2 mL. The order is 250 mg. How many mL to administer?

• A. 2 mL
• B. 3 mL
• C. 5 mL
• D. 4 mL

Answer: (D)

You use the concentration to find how much medicine corresponds to the required dose. The vial has 125 mg in 2 mL, which is 125/2 = 62.5 mg per mL. To get 250 mg, divide 250 by 62.5 mg/mL: 250 / 62.5 = 4 mL. So you should administer 4 mL. Doubling the dose from 125 mg to 250 mg requires doubling the volume (2 mL × 2 = 4 mL). A smaller volume like 3 mL would deliver only 187.5 mg, and a larger volume like 5 mL would deliver 312.5 mg, not the prescribed amount.