Geometric dilution technique MCQs With Answer

Introduction: Geometric dilution is a foundational pharmacy compounding technique used to achieve uniform distribution of a potent drug present in a small amount within a large quantity of diluent. By sequentially mixing the active with equal portions of excipient to “double” the blend each step, pharmacists ensure homogeneity, minimize content uniformity errors, and prevent dose variability. This method is critical for powders, capsules, and semisolid formulations (ointments, creams), and relies on proper trituration, mortar and pestle selection, matching particle size, and controlling segregation. Key concepts include aliquot vs geometric dilution, eutectic mixtures with adsorbents, blend uniformity testing, and excipient compatibility. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What is the primary purpose of geometric dilution in pharmacy compounding?

• To increase bulk density of powders
• To achieve uniform distribution of a small amount of drug in a large quantity of diluent
• To improve drug solubility in water
• To sterilize powders before filling

Correct Answer: To achieve uniform distribution of a small amount of drug in a large quantity of diluent

Q2. In geometric dilution of powders, each step typically involves adding:

• An arbitrary amount of diluent
• An amount of diluent equal to the weight of the mixture present
• Half the weight of the original drug
• All remaining diluent at once

Correct Answer: An amount of diluent equal to the weight of the mixture present

Q3. Geometric dilution is especially indicated when the active ingredient is:

• Present in a very small proportion relative to the diluent
• Highly water-soluble
• Administered parenterally
• Light-insensitive

Correct Answer: Present in a very small proportion relative to the diluent

Q4. Which mortar is generally preferred for triturating crystalline powders during geometric dilution?

• Glass mortar
• Wedgewood mortar
• Stainless steel bowl
• Plastic beaker

Correct Answer: Wedgewood mortar

Q5. When mixing a potent colored drug to avoid staining and adsorption, which mortar is preferred?

• Wedgewood mortar
• Porcelain mortar
• Glass mortar
• Wooden bowl

Correct Answer: Glass mortar

Q6. The first portion of diluent added in geometric dilution should be approximately equal to the:

• Final batch weight
• Weight of the active drug
• Weight of all excipients combined
• Volume of the blend

Correct Answer: Weight of the active drug

Q7. Which sequence best describes geometric dilution with trituration?

• Add entire diluent, then triturate briefly
• Add equal weight of diluent to the existing mix, triturate thoroughly, and repeat
• Sprinkle drug into diluent while stirring with a spatula only
• Mix by shaking in a bag without size reduction

Correct Answer: Add equal weight of diluent to the existing mix, triturate thoroughly, and repeat

Q8. In ointment preparation, geometric dilution is commonly combined with which technique to disperse hydrophobic powders?

• Percolation
• Levigation with a small amount of wetting agent
• Lyophilization
• Steam sterilization

Correct Answer: Levigation with a small amount of wetting agent

Q9. You have 0.5 g of drug to prepare a 120 g powder blend by geometric dilution. What should be the weight of the first diluent portion?

• 120 g
• 60 g
• 0.5 g
• 1.0 g

Correct Answer: 0.5 g

Q10. Starting with 0.25 g of active, after four geometric additions (each time adding diluent equal to current mix), the total blend weight will be:

• 1.0 g
• 2.0 g
• 4.0 g
• 8.0 g

Correct Answer: 4.0 g

Q11. The minimum number of geometric additions needed to reach at least 1,000 mg total from 50 mg of drug is:

• 3
• 4
• 5
• 6

Correct Answer: 5

Q12. Geometric dilution primarily controls which risk during mixing?

• Moisture uptake
• Segregation due to particle charge
• Concentration “hot spots” of a potent drug
• Thermal degradation

Correct Answer: Concentration “hot spots” of a potent drug

Q13. Before geometric dilution, reducing and matching particle size between drug and diluent helps to minimize:

• Percolation segregation
• pH-dependent solubility
• Hygroscopicity
• Odor

Correct Answer: Percolation segregation

Q14. Which statement about arithmetic vs geometric dilution is correct?

• Arithmetic adds a constant mass each step; geometric doubles the mixture each step
• Arithmetic doubles the mixture each step; geometric adds a constant mass
• Both add all diluent at once
• Both are serial dilutions in liquids

Correct Answer: Arithmetic adds a constant mass each step; geometric doubles the mixture each step

Q15. For capsule filling after geometric dilution, which practice best preserves blend uniformity?

• Prolonged vibration of the hopper
• Avoiding excessive tapping and minimizing drop height
• Using widely polydisperse excipients
• Drying the blend at high temperature

Correct Answer: Avoiding excessive tapping and minimizing drop height

Q16. Which is the most appropriate diluent selection criterion for geometric dilution with a potent API?

• Bright color to visualize mixing
• Chemical compatibility and similar particle size/density to the API
• Highest possible bulk density
• Strong electrostatic charge

Correct Answer: Chemical compatibility and similar particle size/density to the API

Q17. In handling eutectic mixtures (e.g., menthol and camphor) using geometric dilution, a best practice is to:

• Heat the powders to 60°C before mixing
• Mix each with an adsorbent (e.g., light MgO) by geometric dilution, then combine
• Add water to prevent liquefaction
• Compress immediately into tablets

Correct Answer: Mix each with an adsorbent (e.g., light MgO) by geometric dilution, then combine

Q18. The aliquot method differs from geometric dilution because it primarily improves:

• Measurement accuracy of small quantities
• Flowability of powders
• Moisture resistance
• Color uniformity only

Correct Answer: Measurement accuracy of small quantities

Q19. A common error that defeats the purpose of geometric dilution is:

• Adding equal weights of diluent at each step
• Adding the entire remaining diluent at the final step
• Using a wedgewood mortar for trituration
• Sieving powders to a similar size

Correct Answer: Adding the entire remaining diluent at the final step

Q20. Which practical indicator most reliably confirms adequate uniformity after geometric dilution in a teaching lab?

• Blend appears glossy
• Uniform color tracer and consistent assay of replicate aliquots
• Blend temperature is ambient
• Mortar walls are evenly coated

Correct Answer: Uniform color tracer and consistent assay of replicate aliquots

Q21. For semisolids, the correct application of geometric dilution is to:

• Add full base to the drug at once and stir quickly
• First incorporate the drug into a small portion of base, then double the base sequentially
• Add volatile oils first, then the drug
• Rely only on levigation without stepwise dilution

Correct Answer: First incorporate the drug into a small portion of base, then double the base sequentially

Q22. Which situation is most likely to cause segregation after geometric dilution?

• Matching particle size distributions
• Large differences in particle size and density between components
• Minimal handling after mixing
• Use of anti-static measures

Correct Answer: Large differences in particle size and density between components

Q23. Geometric dilution is best suited for which types of formulations?

• Solutions only
• Powders and semisolid bases
• Gases and aerosols
• Parenteral emulsions

Correct Answer: Powders and semisolid bases

Q24. During geometric dilution, trituration primarily serves to:

• Increase hygroscopicity
• Reduce particle size and enhance intimate contact between components
• Raise the melting point
• Neutralize acidic drugs

Correct Answer: Reduce particle size and enhance intimate contact between components

Q25. The correct order when multiple actives of different strengths are present is to start with the:

• Largest-quantity component
• Component with highest density
• Smallest-quantity (most potent) component
• Component with best flow

Correct Answer: Smallest-quantity (most potent) component

Q26. Which statement about “doubling” in geometric dilution is accurate?

• Each step adds diluent equal to the original drug amount only
• Each step adds diluent equal to the current mixture weight, doubling total mass each time
• Each step triples the mass
• It applies only to liquids

Correct Answer: Each step adds diluent equal to the current mixture weight, doubling total mass each time

Q27. If starting with 0.3125 g of drug, the minimum number of geometric additions to reach at least 20 g total is:

• 4
• 5
• 6
• 7

Correct Answer: 6

Q28. To minimize electrostatic effects during geometric dilution of fine powders, the best approach is to:

• Work in low humidity and plastic containers
• Use an anti-static device and avoid plastic where possible
• Add water to the blend
• Heat the mixture to 60°C

Correct Answer: Use an anti-static device and avoid plastic where possible

Q29. Which statement correctly distinguishes geometric dilution from alligation?

• Both are used to determine tablet hardness
• Geometric dilution is a mixing technique; alligation calculates proportions of components with different strengths
• Alligation is only for semisolids; geometric dilution is only for liquids
• Both require heating to mix

Correct Answer: Geometric dilution is a mixing technique; alligation calculates proportions of components with different strengths

Q30. After completing geometric dilution for a 1% w/w drug powder, which in-process control is most appropriate in the lab?

• Measure blend viscosity
• Assay multiple small samples from different locations for content uniformity
• Check glass transition temperature
• Perform microbial limit testing only

Correct Answer: Assay multiple small samples from different locations for content uniformity

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