CSPT Sterile Compounding Calculations 3 — Questions and Answers
Question 1: A TPN order requires 500 mEq of sodium chloride. How many mL of 23.4% NaCl (4 mEq/mL) are needed?
- 100 mL
- 125 mL (Correct answer)
- 150 mL
- 200 mL
Correct answer: 125 mL
500 mEq ÷ 4 mEq/mL = 125 mL.
Question 2: An IV solution contains 1 g of drug in 250 mL. What is the concentration in mg/mL?
- 0.4 mg/mL
- 2 mg/mL
- 4 mg/mL (Correct answer)
- 40 mg/mL
Correct answer: 4 mg/mL
1 g = 1000 mg; 1000 mg ÷ 250 mL = 4 mg/mL.
Question 3: A pediatric patient weighs 22 lbs. A drug is dosed at 10 mg/kg/day. What is the daily dose?
- 100 mg (Correct answer)
- 200 mg
- 220 mg
- 100 mg
Correct answer: 100 mg
22 lbs ÷ 2.2 = 10 kg; 10 kg × 10 mg/kg = 100 mg/day.
Question 4: You need to prepare 200 mL of a 0.5% solution from a 2% stock solution. How many mL of stock do you need?
- 25 mL
- 50 mL (Correct answer)
- 100 mL
- 40 mL
Correct answer: 50 mL
C1V1 = C2V2 → 2% × V1 = 0.5% × 200 mL → V1 = 50 mL.
Question 5: A continuous infusion is ordered at 15 mL/hr. How many hours will a 250 mL bag last?
- 10 hours
- 12.5 hours
- 15 hours
- 16.7 hours (Correct answer)
Correct answer: 16.7 hours
250 mL ÷ 15 mL/hr ≈ 16.7 hours.
Question 6: A drug has an osmolarity of 1500 mOsm/L. If diluted to 500 mL with D5W, what is the approximate osmolarity?
- 250 mOsm/L
- 500 mOsm/L
- 750 mOsm/L (Correct answer)
- 1000 mOsm/L
Correct answer: 750 mOsm/L
1500 mOsm/L × 1 L ÷ 2 (500 mL dilution) → 750 mOsm/L approximate midpoint.
Question 7: How many milliequivalents of potassium are in 20 mL of potassium chloride 10% (MW KCl = 74.5 g/mol)?
- 13.4 mEq
- 26.8 mEq (Correct answer)
- 40 mEq
- 53.6 mEq
Correct answer: 26.8 mEq
20 mL × 0.10 g/mL = 2 g; 2000 mg ÷ 74.5 mg/mEq = 26.8 mEq.
CSPT Sterile Compounding Calculations 3
A TPN order requires 500 mEq of sodium chloride.
How many mL of 23.4% NaCl (4 mEq/mL) are needed?