To reconstitute a 1 g vial of a freeze-dried drug to yield a 4% solution, what volume of diluent do you need to add?

To reconstitute a 1 g vial of a freeze-dried drug to yield a 4% solution, what volume of diluent do you need to add?

• A. 4 mL
• B. 20 mL
• C. 25 mL
• D. 40 mL

Answer: (C)

A 4% solution means 4 g per 100 mL, or 0.04 g per milliliter. If you have 1 g of drug, you need enough diluent to reach a volume where each milliliter contains 0.04 g: 1 g ÷ 0.04 g/mL = twenty-five milliliters. So the final volume should be twenty-five milliliters to yield a 4% solution. That gives 1 g in twenty-five milliliters, which is 0.04 g/mL or 4% w/v. If you used less or more volume, the concentration would be higher or lower than 4%.

A 4% solution means 4 g per 100 mL, or 0.04 g per milliliter. If you have 1 g of drug, you need enough diluent to reach a volume where each milliliter contains 0.04 g: 1 g ÷ 0.04 g/mL = twenty-five milliliters. So the final volume should be twenty-five milliliters to yield a 4% solution. That gives 1 g in twenty-five milliliters, which is 0.04 g/mL or 4% w/v. If you used less or more volume, the concentration would be higher or lower than 4%.