A stock is 15 mg/mL. The ordered dose is 7.5 mg. How many mL should be given?

A stock is 15 mg/mL. The ordered dose is 7.5 mg. How many mL should be given?

• A. 0.25 mL
• B. 0.5 mL
• C. 1 mL
• D. 1.5 mL

Answer: (B)

Concentration tells us how much drug is in each milliliter. Here, 15 mg are in 1 mL. To obtain 7.5 mg, divide the desired dose by the concentration: 7.5 mg ÷ 15 mg/mL = 0.5 mL. So you should administer 0.5 mL. In other words, since 7.5 mg is half of 15 mg, you need half of 1 mL, which is 0.5 mL.

Concentration tells us how much drug is in each milliliter. Here, 15 mg are in 1 mL. To obtain 7.5 mg, divide the desired dose by the concentration: 7.5 mg ÷ 15 mg/mL = 0.5 mL. So you should administer 0.5 mL. In other words, since 7.5 mg is half of 15 mg, you need half of 1 mL, which is 0.5 mL.