A drug has a concentration of 250 mg per 5 mL. How many milliliters are needed to deliver a 25 mg dose?

A drug has a concentration of 250 mg per 5 mL. How many milliliters are needed to deliver a 25 mg dose?

• A. 0.5 mL
• B. 1 mL
• C. 2 mL
• D. 5 mL

Answer: (A)

This question tests converting a dose to the volume using the drug’s concentration. From 250 mg in 5 mL, the concentration is 250 ÷ 5 = 50 mg per mL. To deliver 25 mg, use Volume = Dose ÷ (mg per mL) = 25 mg ÷ 50 mg/mL = 0.5 mL. So you need 0.5 mL to give 25 mg. For context, 1 mL would deliver 50 mg, 2 mL would deliver 100 mg, and 5 mL would deliver 250 mg, which shows why those options are not correct.

This question tests converting a dose to the volume using the drug’s concentration. From 250 mg in 5 mL, the concentration is 250 ÷ 5 = 50 mg per mL. To deliver 25 mg, use Volume = Dose ÷ (mg per mL) = 25 mg ÷ 50 mg/mL = 0.5 mL. So you need 0.5 mL to give 25 mg.

For context, 1 mL would deliver 50 mg, 2 mL would deliver 100 mg, and 5 mL would deliver 250 mg, which shows why those options are not correct.