To draw into a syringe 100 mg of a preparation at a concentration of 25 mg/mL, what volume is needed?

To draw into a syringe 100 mg of a preparation at a concentration of 25 mg/mL, what volume is needed?

• A. 4 mL
• B. 8 mL
• C. 10 mL
• D. 25 mL

Answer: (A)

To determine the volume you need, use the relationship: volume = mass ÷ concentration. You want 100 mg from a solution that has 25 mg per mL. Dividing 100 mg by 25 mg/mL gives 4 mL. The units mg cancel, leaving mL, so you must draw 4 mL to obtain 100 mg. This is the amount you would pull into the syringe to deliver the desired dose.

To determine the volume you need, use the relationship: volume = mass ÷ concentration. You want 100 mg from a solution that has 25 mg per mL. Dividing 100 mg by 25 mg/mL gives 4 mL. The units mg cancel, leaving mL, so you must draw 4 mL to obtain 100 mg. This is the amount you would pull into the syringe to deliver the desired dose.