20 Sterile Compounding Calculations Practice Questions & Answers

Every Sterile Compounding Calculations practice question from the CSPT Sterile Compounding Practice Test, with the correct answer and a short explanation.

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1. An order calls for 675 mcg of a drug to be added to a minibag. The vial on the counter is labeled 0.5 mg/mL. How many milliliters must be withdrawn?
- A.0.74 mL
- B.1.35 mL✓ Answer
- C.0.68 mL
- D.13.5 mL
Both quantities must be in the same unit before a proportion can be set up: 675 mcg divided by 1,000 is 0.675 mg, and 0.675 mg divided by 0.5 mg/mL gives 1.35 mL. Skipping the microgram-to-milligram step is what produces a ten-fold answer, the classic fatal error at the hood.
Source: PTCB CSPT Content Outline, Sterile Compounding Procedures — conversions, ratios and proportions used to prepare compounded sterile preparationsReport a problem with this question
2. A 500 mL bag is labeled 1.5% w/v. How many grams of drug does the bag contain?
- A.0.75 g
- B.7.5 g✓ Answer
- C.15 g
- D.75 g
Percent weight in volume is defined as grams of solute per 100 mL of finished preparation, so 1.5% w/v is 1.5 g per 100 mL. Multiplying by five 100 mL portions in the 500 mL bag gives 7.5 g; the 15 g answer treats the bag as a full liter.
Source: PTCB CSPT Content Outline, Sterile Compounding Procedures — percent solutions and concentrationsReport a problem with this question
3. A 1,000 mL sterile irrigation solution must contain 2.5% v/v of a liquid concentrate. How many milliliters of the concentrate are needed?
- A.25 mL✓ Answer
- B.250 mL
- C.40 mL
- D.2.5 mL
Percent volume in volume means milliliters of the liquid ingredient per 100 mL of finished preparation, so 2.5% v/v is 2.5 mL per 100 mL. A 1,000 mL preparation contains ten such portions, giving 25 mL; the 40 mL answer comes from inverting the proportion.
Source: PTCB CSPT Content Outline, Sterile Compounding Procedures — percent solutions and concentrationsReport a problem with this question
4. A 5 g tube of sterile ophthalmic ointment is compounded at 3.5% w/w. How many milligrams of active drug does the finished tube contain?
- A.17.5 mg
- B.1,750 mg
- C.175 mg✓ Answer
- D.350 mg
Percent weight in weight is grams of drug per 100 g of finished preparation, so 3.5% w/w equals 0.035 g of drug in every gram. Five grams therefore hold 0.175 g, which converts to 175 mg; the other answers are decimal slips of that same product.
Source: PTCB CSPT Content Outline, Sterile Compounding Procedures — percent solutions and quantities of componentsReport a problem with this question
5. A sterile solution is labeled as a 1:5,000 w/v ratio strength. Which expression is equivalent?
- A.0.02% w/v, equal to 0.2 mg/mL✓ Answer
- B.0.2% w/v, equal to 2 mg/mL
- C.0.5% w/v, equal to 5 mg/mL
- D.2% w/v, equal to 20 mg/mL
A w/v ratio strength of 1:5,000 means 1 g of solute in 5,000 mL, which is 1,000 mg in 5,000 mL, or 0.2 mg/mL. Scaling the same ratio to 100 mL gives 0.02 g per 100 mL, and grams per 100 mL is the definition of percent w/v.
Source: PTCB CSPT Content Outline, Sterile Compounding Procedures — ratio strength and percent strength conversionsReport a problem with this question
6. A vial is labeled 100 mg per 4 mL. The order is for 65 mg. What volume must be withdrawn?
- A.3.25 mL
- B.0.65 mL
- C.16.25 mL
- D.2.6 mL✓ Answer
The labeled vial concentration reduces to 100 mg divided by 4 mL, or 25 mg/mL, and the ordered 65 mg divided by 25 mg/mL is 2.6 mL. The 16.25 mL answer comes from inverting the proportion, and a glance at the 4 mL vial size shows it cannot be right.
Source: PTCB CSPT Content Outline, Sterile Compounding Procedures — ratios and proportions applied to doses withdrawn from a vialReport a problem with this question
7. You must prepare 250 mL of a 3% w/v solution from a 15% w/v concentrate. How many milliliters of sterile diluent are added to the concentrate?
- A.250 mL
- B.200 mL✓ Answer
- C.50 mL
- D.150 mL
Because the amount of drug does not change during a dilution, C1V1 equals C2V2, so the concentrate volume is 3 times 250 divided by 15, or 50 mL. The diluent is the difference between the final volume and that concentrate volume, 250 minus 50, which is 200 mL.
Source: PTCB CSPT Content Outline, Sterile Compounding Procedures — dilutions of concentrated solutionsReport a problem with this question
8. A vial contains 1 g of drug as a dry powder. The package insert directs adding 3.6 mL of diluent, which yields a final volume of 4 mL. What is the concentration of the reconstituted solution?
- A.400 mg/mL
- B.250 mg/mL✓ Answer
- C.200 mg/mL
- D.278 mg/mL
The dry powder itself occupies space, so the final volume of 4 mL exceeds the 3.6 mL of diluent added, and concentration is always drug amount divided by final volume: 1,000 mg divided by 4 mL is 250 mg/mL. Dividing by the 3.6 mL diluent gives 278 mg/mL and would cause too small a volume to be drawn.
Source: USP General Chapter <797> Pharmaceutical Compounding — Sterile Preparations, reconstitution according to the manufacturer's labelingReport a problem with this question
9. Using 70% dextrose and 10% dextrose, you must prepare 1,000 mL of 25% dextrose. How much of the 70% dextrose is needed?
- A.357 mL
- B.750 mL
- C.250 mL✓ Answer
- D.150 mL
In alligation the parts of the stronger stock equal the desired strength minus the weaker one, 25 minus 10, which is 15 parts, while the weaker gets 70 minus 25, or 45 parts, for 60 parts total. Fifteen sixtieths of 1,000 mL is 250 mL, and the check confirms it: 175 g plus 75 g is 250 g of dextrose in 1,000 mL.
Source: PTCB CSPT Content Outline, Sterile Compounding Procedures — alligation of two available strengthsReport a problem with this question
10. Using 70% dextrose and sterile water for injection, you must prepare 500 mL of a 14% dextrose solution. How much sterile water is needed?
- A.430 mL
- B.350 mL
- C.100 mL
- D.400 mL✓ Answer
Sterile water counts as a 0% strength, so the parts of the 70% stock are 14 minus 0 and the parts of water are 70 minus 14, giving 14 and 56 parts out of 70. Fifty-six seventieths of 500 mL is 400 mL of water, leaving 100 mL of the 70% stock, which supplies 70 g of dextrose in 500 mL.
Source: PTCB CSPT Content Outline, Sterile Compounding Procedures — alligation and dilution with a diluent of zero strengthReport a problem with this question
11. A 250 mL bag has 30 mL of drug added to it, and the entire 280 mL is infused at 80 mL/hr. How long will the infusion run?
- A.4 hours
- B.3 hours 8 minutes
- C.3 hours 30 minutes✓ Answer
- D.3 hours
Infusion time is total volume divided by rate, and the volume that actually infuses includes the drug added to the bag, so 280 mL divided by 80 mL/hr is 3.5 hours. The decimal 0.5 hour is converted by multiplying by 60, giving 3 hours 30 minutes; using only the 250 mL bag volume yields the short answer.
Source: PTCB CSPT Content Outline, Sterile Compounding Procedures — infusion times and ratesReport a problem with this question
12. An infusion is ordered to run at 150 mL/hr using an administration set with a drop factor of 15 gtt/mL. What is the drip rate?
- A.50 gtt/min
- B.25 gtt/min
- C.150 gtt/min
- D.38 gtt/min✓ Answer
Drops per minute equal the hourly rate multiplied by the drop factor and divided by 60 minutes, so 150 times 15 divided by 60 is 37.5, rounded to 38 because a drop cannot be split. Leaving out the division by 60 gives the 150 gtt/min answer.
Source: PTCB CSPT Content Outline, Sterile Compounding Procedures — infusion rate calculations using a set drop factorReport a problem with this question
13. A pump is infusing a bag containing 400 mg of drug in 250 mL at 15 mL/hr. The technician's worksheet records the delivered dose as 24,000 mcg/min. Which statement correctly evaluates that entry?
- A.It is the amount delivered per hour; the true rate is 400 mcg/min.✓ Answer
- B.It is correct as recorded; the true rate is 24,000 mcg/min.
- C.It uses bag volume as the rate; the true rate is 1,600 mcg/min.
- D.It omits the mg-to-mcg step; the true rate is 24 mcg/min.
The bag concentration is 400 mg in 250 mL, or 1,600 mcg/mL, so a rate of 15 mL/hr delivers 24,000 mcg every hour, not every minute. Dividing that hourly figure by 60 minutes gives the true 400 mcg/min, and the missing per-hour to per-minute step is the most common slip in critical-care rate work.
Source: PTCB CSPT Content Outline, Sterile Compounding Procedures — dose per unit time and verification of compounding calculationsReport a problem with this question
14. A 70 kg patient is ordered a drug at 5 mcg/kg/min. The bag contains 200 mg of the drug in 250 mL. At what rate should the pump be set?
- A.0.44 mL/hr
- B.52.5 mL/hr
- C.21 mL/hr
- D.26.25 mL/hr✓ Answer
The bag concentration is 200 mg in 250 mL, which is 200,000 mcg divided by 250 mL, or 800 mcg/mL. The ordered dose is 5 times 70, or 350 mcg/min, and multiplying by 60 minutes gives 21,000 mcg/hr, which divided by 800 mcg/mL sets the pump at 26.25 mL/hr; omitting the times-60 step produces 0.44 mL/hr.
Source: PTCB CSPT Content Outline, Sterile Compounding Procedures — weight-based dose rates converted to pump ratesReport a problem with this question
15. A patient weighs 165 lb. The order is 3 mg/kg and the vial contains 50 mg/mL. Given that 1 kg equals 2.2 lb, what volume delivers the dose?
- A.6.75 mL
- B.4.5 mL✓ Answer
- C.9.9 mL
- D.2.25 mL
Weight-based orders are written per kilogram, so the pounds must be converted first: 165 divided by 2.2 is 75 kg. Multiplying 75 kg by 3 mg/kg gives 225 mg, and 225 mg divided by 50 mg/mL is 4.5 mL; dosing straight from pounds gives the 9.9 mL overdose.
Source: PTCB CSPT Content Outline, Sterile Compounding Procedures — weight-based doses and unit conversionsReport a problem with this question
16. A chemotherapy order reads 75 mg/m2. The patient's body surface area is 1.8 m2 and the vial contains 25 mg/mL. What volume must be withdrawn?
- A.5.4 mL✓ Answer
- B.0.54 mL
- C.54 mL
- D.3 mL
A dose written in mg per square meter must be multiplied by the patient's body surface area before any volume is figured, so 75 mg/m2 times 1.8 m2 is 135 mg. Dividing 135 mg by the 25 mg/mL vial concentration gives 5.4 mL, while dividing 75 by 25 ignores the body surface area entirely.
Source: PTCB CSPT Content Outline, Sterile Compounding Procedures — body surface area dosing for compounded sterile preparationsReport a problem with this question
17. A home infusion patient receives 750 mg of a drug every 12 hours for 7 days. The drug comes only in 500 mg single-dose vials, and any contents remaining after a dose are discarded. How many vials must be dispensed?
- A.42 vials
- B.28 vials✓ Answer
- C.21 vials
- D.14 vials
Dosing every 12 hours is two doses a day, so 7 days is 14 doses, and each 750 mg dose needs part of a second 500 mg vial. Because a single-dose vial cannot be held over for the next dose, each dose consumes two vials and 14 times 2 is 28; dividing the 10,500 mg total by 500 mg gives 21 and wrongly assumes leftovers can be pooled.
Source: USP General Chapter <797> Pharmaceutical Compounding — Sterile Preparations, use of single-dose containers, with PTCB CSPT Content Outline, dispensing quantities and days supplyReport a problem with this question
18. A parenteral nutrition order requires 175 g of dextrose. The pharmacy stocks 70% dextrose injection. What volume of the 70% dextrose is needed?
- A.2,500 mL
- B.175 mL
- C.122.5 mL
- D.250 mL✓ Answer
A 70% w/v solution carries 70 g in every 100 mL, which is 0.7 g per milliliter, so the volume needed is the grams ordered divided by that strength: 175 divided by 0.7 is 250 mL. Multiplying 175 by 0.7 instead of dividing gives the 122.5 mL answer and would shortchange the patient's dextrose.
Source: PTCB CSPT Content Outline, Sterile Compounding Procedures — parenteral nutrition component volumes from stock concentrationsReport a problem with this question
19. A 2,000 mL parenteral nutrition bag contains 250 mL of 70% dextrose, 600 mL of 15% amino acids, 250 mL of 20% lipid emulsion, and 60 mL of electrolytes and additives. How much sterile water for injection is added to reach the final volume?
- A.840 mL✓ Answer
- B.1,090 mL
- C.1,160 mL
- D.900 mL
Sterile water is the make-up volume, so every other component must be summed first: 250 plus 600 plus 250 plus 60 is 1,160 mL. Subtracting that from the ordered 2,000 mL leaves 840 mL, and forgetting the 60 mL of electrolytes and additives is what produces the 900 mL answer.
Source: PTCB CSPT Content Outline, Sterile Compounding Procedures — parenteral nutrition compounding and final volume make-upReport a problem with this question
20. An order calls for 0.4 mg. The vial is labeled 2 mg per 5 mL, and the technician draws up 10 mL. Which statement correctly evaluates the volume drawn?
- A.One-tenth of the correct volume; 100 mL would contain 0.4 mg.
- B.Twice the correct volume; 5 mL of the vial contains 0.4 mg.
- C.Ten times the correct volume; 1 mL of the vial contains 0.4 mg.✓ Answer
- D.The correct volume; 10 mL of the vial contains 0.4 mg.
The labeled vial reduces to 2 mg divided by 5 mL, or 0.4 mg/mL, so the ordered 0.4 mg is contained in exactly 1 mL and 10 mL is a tenfold overdose. Estimating the expected magnitude first catches this instantly, since 10 mL is twice the entire vial, and a volume larger than the container should stop the preparation and be rechecked with the pharmacist.
Source: USP General Chapter <797> Pharmaceutical Compounding — Sterile Preparations, verification of calculations and measured volumes before compoundingReport a problem with this question

Practice questions based on the PTCB CSPT Content Outline and the USP General Chapters governing sterile compounding. CSPT and PTCB are marks of the Pharmacy Technician Certification Board; this site is not affiliated with or endorsed by PTCB or USP. Standards for sterile compounding are revised periodically and your state board of pharmacy and your employer's policies also apply — always follow your facility's current procedures and confirm current requirements before testing. About the CSPT exam →

1. An order calls for 675 mcg of a drug to be added to a minibag. The vial on the counter is labeled 0.5 mg/mL. How many milliliters must be withdrawn?

2. A 500 mL bag is labeled 1.5% w/v. How many grams of drug does the bag contain?

3. A 1,000 mL sterile irrigation solution must contain 2.5% v/v of a liquid concentrate. How many milliliters of the concentrate are needed?

4. A 5 g tube of sterile ophthalmic ointment is compounded at 3.5% w/w. How many milligrams of active drug does the finished tube contain?

5. A sterile solution is labeled as a 1:5,000 w/v ratio strength. Which expression is equivalent?

6. A vial is labeled 100 mg per 4 mL. The order is for 65 mg. What volume must be withdrawn?

7. You must prepare 250 mL of a 3% w/v solution from a 15% w/v concentrate. How many milliliters of sterile diluent are added to the concentrate?

8. A vial contains 1 g of drug as a dry powder. The package insert directs adding 3.6 mL of diluent, which yields a final volume of 4 mL. What is the concentration of the reconstituted solution?

9. Using 70% dextrose and 10% dextrose, you must prepare 1,000 mL of 25% dextrose. How much of the 70% dextrose is needed?

10. Using 70% dextrose and sterile water for injection, you must prepare 500 mL of a 14% dextrose solution. How much sterile water is needed?

11. A 250 mL bag has 30 mL of drug added to it, and the entire 280 mL is infused at 80 mL/hr. How long will the infusion run?

12. An infusion is ordered to run at 150 mL/hr using an administration set with a drop factor of 15 gtt/mL. What is the drip rate?

13. A pump is infusing a bag containing 400 mg of drug in 250 mL at 15 mL/hr. The technician's worksheet records the delivered dose as 24,000 mcg/min. Which statement correctly evaluates that entry?

14. A 70 kg patient is ordered a drug at 5 mcg/kg/min. The bag contains 200 mg of the drug in 250 mL. At what rate should the pump be set?

15. A patient weighs 165 lb. The order is 3 mg/kg and the vial contains 50 mg/mL. Given that 1 kg equals 2.2 lb, what volume delivers the dose?

16. A chemotherapy order reads 75 mg/m2. The patient's body surface area is 1.8 m2 and the vial contains 25 mg/mL. What volume must be withdrawn?

17. A home infusion patient receives 750 mg of a drug every 12 hours for 7 days. The drug comes only in 500 mg single-dose vials, and any contents remaining after a dose are discarded. How many vials must be dispensed?

18. A parenteral nutrition order requires 175 g of dextrose. The pharmacy stocks 70% dextrose injection. What volume of the 70% dextrose is needed?

19. A 2,000 mL parenteral nutrition bag contains 250 mL of 70% dextrose, 600 mL of 15% amino acids, 250 mL of 20% lipid emulsion, and 60 mL of electrolytes and additives. How much sterile water for injection is added to reach the final volume?

20. An order calls for 0.4 mg. The vial is labeled 2 mg per 5 mL, and the technician draws up 10 mL. Which statement correctly evaluates the volume drawn?