A stock medication is 100 mg/mL. If a patient requires 25 mg, how many milliliters should be administered?

• A. 0.25 mL
• B. 0.5 mL
• C. 2.5 mL
• D. 0.025 mL

Answer: (A)

Converting a drug dose from milligrams to milliliters using the amount of drug in each milliliter. If a stock solution has 100 mg per 1 mL, that means every 1 mL contains 100 mg. To find the volume that provides 25 mg, divide the desired dose by the concentration: 25 mg ÷ (100 mg/mL) = 0.25 mL. So administer 0.25 mL, which is a quarter of a milliliter.

For context, 0.5 mL would deliver 50 mg, which is too high; 2.5 mL would deliver 250 mg, far too high; 0.025 mL would deliver 2.5 mg, far too low. Always confirm syringe capability to accurately measure 0.25 mL.