Pharm.D. Doctor of Pharmacy Pharmaceutical Calculations and Compounding 2 — Questions and Answers
Question 1: A pharmacist prepares a compound by mixing 30 g of a 2.5% hydrocortisone cream with 70 g of a plain base. What is the final concentration?
- 0.75% (Correct answer)
- 1.75%
- 2.0%
- 2.5%
Correct answer: 0.75%
Active drug = 30 g × 0.025 = 0.75 g; total weight = 100 g; final concentration = 0.75/100 = 0.75%.
Question 2: Which type of balance is most commonly required by USP standards for prescription compounding?
- Class A prescription balance (sensitivity: 6 mg) (Correct answer)
- Class B analytical balance
- Torsion balance (200 mg sensitivity)
- Spring scale
Correct answer: Class A prescription balance (sensitivity: 6 mg)
USP requires a Class A prescription balance with a sensitivity requirement (SR) of 6 mg for compounding prescriptions involving small quantities.
Question 3: The beyond-use date (BUD) for a non-aqueous compounded preparation in a non-sterile environment, per USP <795>, is:
- 14 days refrigerated
- 6 months or shelf life of the ingredient, whichever is earlier (Correct answer)
- 30 days at room temperature
- 1 year
Correct answer: 6 months or shelf life of the ingredient, whichever is earlier
USP <795> sets the BUD for non-aqueous preparations at the earlier of 6 months or the shortest remaining shelf life of any ingredient.
Question 4: Alligation medial is used to calculate:
- The strength of a mixture of two concentrations of the same drug (Correct answer)
- The weight of solute in a solution
- The osmolarity of an IV solution
- The overfill volume in IV bags
Correct answer: The strength of a mixture of two concentrations of the same drug
Alligation medial (or alternate) is a mathematical shortcut to determine the proportions needed to mix two strengths of a substance to achieve a desired intermediate strength.
Question 5: A prescription calls for 240 mL of a 1:400 w/v solution. How many grams of drug are required?
- 0.24 g
- 0.4 g
- 0.6 g (Correct answer)
- 2.4 g
Correct answer: 0.6 g
1:400 means 1 g per 400 mL; for 240 mL: (1/400) × 240 = 0.6 g.
Question 6: Reducing particle size during compounding through trituration in a mortar and pestle primarily achieves:
- Improved chemical stability
- Enhanced dissolution rate and uniformity of mixing (Correct answer)
- Decreased hygroscopicity
- Increased drug solubility in organic solvents
Correct answer: Enhanced dissolution rate and uniformity of mixing
Trituration reduces particle size, increasing surface area, which enhances dissolution rate and ensures homogeneous distribution throughout the preparation.
Pharm.D. Doctor of Pharmacy Pharmaceutical Calculations and Compounding 2
A pharmacist prepares a compound by mixing 30 g of a 2.5% hydrocortisone cream with 70 g of a plain base.
What is the final concentration?