Reconstitution & Powder Volume Practice
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Reconstituting a powdered drug adds diluent to reach a target concentration, but the dry powder occupies space of its own. That space is the powder volume, or displacement volume, and it makes the final volume greater than the diluent added.
Formulapowder (displacement) volume = final reconstituted volume − volume of diluent added
Worked exampleA 1 g vial reconstituted to 100 mg/mL needs a final volume of 10 mL. If the label says to add 9.5 mL diluent, the powder volume = 10 − 9.5 = 0.5 mL.
Add the displacement volume to the diluent when finding concentration. Leave it out and you overestimate the strength.
10 Reconstitution & Powder Volume practice problems with worked solutions
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Problem 1: Reconstitution
A vial contains 0.5 g of drug with a powder displacement volume of 0.4 mL. If you add 4.5 mL of diluent, what is the final concentration in mg/mL? Round your answer to the nearest whole number.
Answer 102 mg/mL
Solution- Final volume = diluent + powder displacement = 4.5 mL + 0.4 mL = 4.9 mL.
- Concentration = 500 mg ÷ 4.9 mL ≈ 102.04 mg/mL.
- Rounded as the question asks: 102 mg/mL.
Add the powder's displacement volume to the diluent. Leave it out and you overestimate the concentration.
Problem 2: Reconstitution
A vial contains 2 g of drug with a powder displacement volume of 0.7 mL. If you add 4.6 mL of diluent, what is the final concentration in mg/mL? Round your answer to the nearest whole number.
Answer 377 mg/mL
Solution- Final volume = diluent + powder displacement = 4.6 mL + 0.7 mL = 5.3 mL.
- Concentration = 2000 mg ÷ 5.3 mL ≈ 377.36 mg/mL.
- Rounded as the question asks: 377 mg/mL.
Add the powder's displacement volume to the diluent. Leave it out and you overestimate the concentration.
Problem 3: Reconstitution
A vial contains 0.25 g of drug with a powder displacement volume of 0.5 mL. If you add 1.8 mL of diluent, what is the final concentration in mg/mL? Round your answer to the nearest whole number.
Answer 109 mg/mL
Solution- Final volume = diluent + powder displacement = 1.8 mL + 0.5 mL = 2.3 mL.
- Concentration = 250 mg ÷ 2.3 mL ≈ 108.7 mg/mL.
- Rounded as the question asks: 109 mg/mL.
Add the powder's displacement volume to the diluent. Leave it out and you overestimate the concentration.
Problem 4: Reconstitution
A vial contains 1 g of drug with a powder displacement volume of 0.7 mL. If you add 9.5 mL of diluent, what is the final concentration in mg/mL? Round your answer to the nearest whole number.
Answer 98 mg/mL
Solution- Final volume = diluent + powder displacement = 9.5 mL + 0.7 mL = 10.2 mL.
- Concentration = 1000 mg ÷ 10.2 mL ≈ 98.04 mg/mL.
- Rounded as the question asks: 98 mg/mL.
Add the powder's displacement volume to the diluent. Leave it out and you overestimate the concentration.
Problem 5: Reconstitution
A vial contains 2 g of drug with a powder displacement volume of 0.4 mL. If you add 4.6 mL of diluent, what is the final concentration in mg/mL? Round your answer to the nearest whole number.
Answer 400 mg/mL
Solution- Final volume = diluent + powder displacement = 4.6 mL + 0.4 mL = 5 mL.
- Concentration = 2000 mg ÷ 5 mL = 400 mg/mL.
- Rounded as the question asks: 400 mg/mL.
Add the powder's displacement volume to the diluent. Leave it out and you overestimate the concentration.
Problem 6: Reconstitution
A vial contains 1 g of powdered drug. Adding 2.1 mL of diluent yields a final concentration of 400 mg/mL. What is the powder (displacement) volume? Round your answer to two decimal places.
Answer 0.40 mL
Solution- Final volume needed: 1 g = 1000 mg; 1000 mg ÷ 400 mg/mL = 2.5 mL.
- Powder volume = final volume − diluent added = 2.5 − 2.1 = 0.4 mL.
- Rounded as the question asks: 0.40 mL.
The dry powder occupies space (displacement). Powder volume = final reconstituted volume − volume of diluent added.
Problem 7: Reconstitution
A vial contains 2 g of powdered drug. Adding 4.6 mL of diluent yields a final concentration of 400 mg/mL. What is the powder (displacement) volume? Round your answer to two decimal places.
Answer 0.40 mL
Solution- Final volume needed: 2 g = 2000 mg; 2000 mg ÷ 400 mg/mL = 5 mL.
- Powder volume = final volume − diluent added = 5 − 4.6 = 0.4 mL.
- Rounded as the question asks: 0.40 mL.
The dry powder occupies space (displacement). Powder volume = final reconstituted volume − volume of diluent added.
Problem 8: Reconstitution
A vial contains 3 g of powdered drug. Adding 23.4 mL of diluent yields a final concentration of 125 mg/mL. What is the powder (displacement) volume? Round your answer to two decimal places.
Answer 0.60 mL
Solution- Final volume needed: 3 g = 3000 mg; 3000 mg ÷ 125 mg/mL = 24 mL.
- Powder volume = final volume − diluent added = 24 − 23.4 = 0.6 mL.
- Rounded as the question asks: 0.60 mL.
The dry powder occupies space (displacement). Powder volume = final reconstituted volume − volume of diluent added.
Problem 9: Reconstitution
A vial contains 1 g of powdered drug. Adding 3.6 mL of diluent yields a final concentration of 250 mg/mL. What is the powder (displacement) volume? Round your answer to two decimal places.
Answer 0.40 mL
Solution- Final volume needed: 1 g = 1000 mg; 1000 mg ÷ 250 mg/mL = 4 mL.
- Powder volume = final volume − diluent added = 4 − 3.6 = 0.4 mL.
- Rounded as the question asks: 0.40 mL.
The dry powder occupies space (displacement). Powder volume = final reconstituted volume − volume of diluent added.
Problem 10: Reconstitution
A vial contains 1 g of drug with a powder displacement volume of 0.7 mL. If you add 2.5 mL of diluent, what is the final concentration in mg/mL? Round your answer to the nearest whole number.
Answer 313 mg/mL
Solution- Final volume = diluent + powder displacement = 2.5 mL + 0.7 mL = 3.2 mL.
- Concentration = 1000 mg ÷ 3.2 mL = 312.5 mg/mL.
- Rounded as the question asks: 313 mg/mL.
Add the powder's displacement volume to the diluent. Leave it out and you overestimate the concentration.