Displacement value and calculations MCQs With Answer

Introduction

Displacement value (DV) is a core concept in pharmaceutical calculations for B. Pharm students, especially in compounding suppositories and pessaries. Also known as the density factor, DV quantifies the weight of drug that displaces 1 g of base, enabling accurate estimation of base displaced and base required. Mastery of DV helps you calculate mold capacity adjustments, total base required, medicated unit weight, and interpret the impact of density differences between drug and base (e.g., cocoa butter, PEG, glycerogelatin). This topic integrates density, unit conversions, and stepwise problem-solving to minimize compounding errors and ensure dose uniformity. Build confidence with definitions, formulas, and real-world numericals. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What is the most accurate definition of displacement value (DV) in suppository calculations?

• Weight of drug that displaces 1 g of base
• Weight of base displaced by 1 g of drug
• Number of suppositories made from 1 g of base
• Ratio of base to drug required per unit

Correct Answer: Weight of drug that displaces 1 g of base

Q2. Which relationship between DV and densities is correct?

• DV = density of drug / density of base
• DV = density of base / density of drug
• DV = density of drug × density of base
• DV = density of drug − density of base

Correct Answer: DV = density of drug / density of base

Q3. If 0.4 g of drug with DV = 4 is used, how much base is displaced?

• 0.10 g
• 0.16 g
• 1.60 g
• 0.04 g

Correct Answer: 0.10 g

Q4. A blank suppository (Wb) weighs 2.0 g. Each unit contains 0.3 g drug with DV = 3. How much base is required per unit?

• 1.90 g
• 2.10 g
• 1.80 g
• 2.30 g

Correct Answer: 1.90 g

Q5. For 12 suppositories (Wb = 1.8 g each) containing 250 mg drug per unit with DV = 2.5, total base required is:

• 20.4 g
• 18.0 g
• 22.8 g
• 24.0 g

Correct Answer: 20.4 g

Q6. Twenty blank suppositories weigh 30 g total. Twenty medicated suppositories (0.5 g drug each) weigh 34 g total. DV is:

• 1.67
• 0.60
• 1.50
• 3.40

Correct Answer: 1.67

Q7. If DV > 1, what does it indicate?

• Drug is denser than the base
• Drug is less dense than the base
• No relation to density
• Drug and base have equal densities

Correct Answer: Drug is denser than the base

Q8. A formula uses Wb = 2.5 g. Each unit contains Drug A 300 mg (DV 3) and Drug B 200 mg (DV 5). Base required per unit is:

• 2.36 g
• 2.14 g
• 2.64 g
• 2.50 g

Correct Answer: 2.36 g

Q9. If Wb = 2.0 g, drug = 0.4 g, DV = 4, the medicated suppository weight per unit is:

• 2.3 g
• 1.9 g
• 2.4 g
• 2.1 g

Correct Answer: 2.3 g

Q10. Which is the correct formula for base required per unit when multiple actives are present?

• Wb − Σ(ai/DVi)
• Wb + Σ(ai/DVi)
• Wb − Σ(ai × DVi)
• Wb + Σ(ai × DVi)

Correct Answer: Wb − Σ(ai/DVi)

Q11. With base available = 40 g, Wb = 2.25 g, each unit has 0.5 g drug (DV 5). Maximum units from base are:

• 17
• 18
• 19
• 20

Correct Answer: 18

Q12. If density of base is 0.9 g/mL and drug is 1.8 g/mL, DV equals:

• 2.0
• 0.5
• 1.62
• 1.0

Correct Answer: 2.0

Q13. Which statement about mold capacity (Wb) is correct?

• Always determine or use blank weight for the same base; Wb depends on base density
• Once measured with water, Wb is valid for any base
• Wb is a fixed volume, so base choice is irrelevant
• Wb decreases when drug is added, regardless of DV

Correct Answer: Always determine or use blank weight for the same base; Wb depends on base density

Q14. In the Paddock method using density factor (DF), base displaced by A grams of drug equals:

• A/DF
• DF/A
• A × DF
• 1/(A × DF)

Correct Answer: A/DF

Q15. If a drug has DV = 0.8 with a given base, it means:

• Drug is less dense than the base
• Drug is denser than the base
• Drug and base have equal densities
• DV cannot be less than 1

Correct Answer: Drug is less dense than the base

Q16. Base density = 0.95 g/mL and drug density = 1.14 g/mL. DV is approximately:

• 1.2
• 0.83
• 2.09
• 0.19

Correct Answer: 1.2

Q17. How much base is displaced by 150 mg of drug with DV = 3?

• 0.05 g
• 0.15 g
• 0.45 g
• 0.30 g

Correct Answer: 0.05 g

Q18. For 10 suppositories (Wb = 2.0 g), each with 400 mg drug (DV 2), total base required is:

• 18 g
• 20 g
• 16 g
• 14 g

Correct Answer: 18 g

Q19. If 0.8 g of drug displaces 0.32 g of base, the DV is:

• 2.5
• 4.0
• 0.4
• 1.25

Correct Answer: 2.5

Q20. When multiple actives are present, the correct approach to DV application is to:

• Compute base displaced separately for each drug using its DV and sum them
• Use the average DV of all drugs
• Use the smallest DV only
• Ignore DV if total drug < 500 mg

Correct Answer: Compute base displaced separately for each drug using its DV and sum them

Q21. For accurate DV calculations, you should always:

• Convert all masses to grams
• Use any units interchangeably
• Convert masses to moles
• Work only with volumes

Correct Answer: Convert all masses to grams

Q22. If DV is not provided but densities are known, the best estimate is:

• DV = density of drug / density of base
• DV = density of base / density of drug
• DV = 1 for all drugs
• DV = 0.5 × (density of drug + density of base)

Correct Answer: DV = density of drug / density of base

Q23. A medicated suppository weighs 2.8 g; blank Wb = 2.5 g; drug per unit = 0.6 g. DV equals:

• 2.0
• 0.5
• 1.5
• 3.0

Correct Answer: 2.0

Q24. A drug has DV = 4 in cocoa butter. Base displaced by 1 g of this drug is:

• 0.25 g
• 4 g
• Depends only on temperature
• Impossible to determine from DV

Correct Answer: 0.25 g

Q25. Per suppository: Drug A 250 mg (DV 2.0) and Drug B 1 g (DV 1.25); Wb = 2.8 g. Base required per unit is:

• 1.875 g
• 1.925 g
• 1.725 g
• 1.650 g

Correct Answer: 1.875 g

Q26. A student uses Wb + a/DV to compute base per unit. What is the error?

• They added the displaced base instead of subtracting it
• They converted grams to milligrams incorrectly
• They assumed DV = 1
• They used the wrong Wb for the base

Correct Answer: They added the displaced base instead of subtracting it

Q27. Base available = 45 g; Wb = 3 g; each pessary contains 750 mg drug (DV 3). Maximum units from base:

• 15
• 16
• 17
• 18

Correct Answer: 16

Q28. Which is true regarding DV and DF in suppository calculations?

• They are numerically identical when DV is defined as “weight of drug that displaces 1 g of base”
• DF is always the reciprocal of DV
• DF applies only to PEG bases, DV only to cocoa butter
• They cannot be used in the same equation

Correct Answer: They are numerically identical when DV is defined as “weight of drug that displaces 1 g of base”

Q29. Given totals: Wb(total blanks), Wm(total medicated), and A(total drug). The correct formula for DV is:

• DV = A / [Wb − Wm + A]
• DV = [Wb − Wm + A] / A
• DV = A / (Wm − Wb)
• DV = (Wm − A) / Wb

Correct Answer: DV = A / [Wb − Wm + A]

Q30. Wb = 2.2 g; Drug A = 0.3 g (DV 3); Drug B = 0.2 g (DV 2). Medicated weight per unit equals:

• 2.5 g
• 2.4 g
• 2.3 g
• 2.2 g

Correct Answer: 2.5 g

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