A 200 mg in 50 mL solution yields 4 mg/mL. How many milliliters are needed to deliver a 100 mg dose?

• A. 10 mL
• B. 15 mL
• C. 30 mL
• D. 25 mL

Answer: (D)

Understand how concentration links dose to volume. The solution provides 4 mg per milliliter (200 mg in 50 mL). To get a 100 mg dose, use volume = dose ÷ concentration: 100 mg ÷ 4 mg/mL = 25 mL. A quick check: delivering half the total dose requires half the volume, so 50 mL would hold 200 mg, and 25 mL holds 100 mg. Therefore, 25 mL is needed.