Thixotropy in formulations MCQs With Answer

Thixotropy in formulations MCQs With Answer

Thixotropy is a key rheological property in pharmaceutics describing time-dependent shear thinning where viscosity decreases under shear and recovers at rest. B. Pharm students must understand thixotropy for designing stable suspensions, gels, creams and injectables, and for selecting excipients like xanthan gum, carbomers or HPMC. This introduction covers mechanisms, measurement (hysteresis loop, rotational viscometers), differentiation from pseudoplasticity and rheopexy, and formulation implications for drug delivery and stability. Mastery helps optimize mixing, syringeability, spreadability and bioavailability in dosage forms. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What is the primary definition of thixotropy in pharmaceutical formulations?

• A reversible, time-dependent decrease in viscosity under constant shear
• An irreversible increase in viscosity with shear
• A time-independent Newtonian flow behavior
• A behavior where viscosity increases with temperature

Correct Answer: A reversible, time-dependent decrease in viscosity under constant shear

Q2. Which rheological behavior is most often confused with thixotropy?

• Pseudoplasticity (shear-thinning without time dependence)
• Bingham plasticity (yield stress behavior)
• Newtonian flow
• Plastic flow with time-dependent thickening

Correct Answer: Pseudoplasticity (shear-thinning without time dependence)

Q3. Which term describes the opposite of thixotropy where viscosity increases with time under shear?

• Rheopexy
• Newtonianization
• Pseudoplasticity
• Bingham behavior

Correct Answer: Rheopexy

Q4. Which instrument is commonly used to measure thixotropic behavior?

• Rotational viscometer (e.g., cone-and-plate)
• UV-Vis spectrophotometer
• High-performance liquid chromatograph
• Thermogravimetric analyzer

Correct Answer: Rotational viscometer (e.g., cone-and-plate)

Q5. What is a hysteresis loop in rheology related to thixotropy?

• The area between up and down shear-rate vs shear-stress curves indicating structural breakdown
• The temperature-viscosity curve for a Newtonian fluid
• The chromatogram of excipient purity
• The pH titration curve of a buffer

Correct Answer: The area between up and down shear-rate vs shear-stress curves indicating structural breakdown

Q6. Which excipient is commonly used to impart thixotropic properties in topical gels?

• Carbomer (carbopol)
• Sodium chloride
• Magnesium stearate
• Lactose monohydrate

Correct Answer: Carbomer (carbopol)

Q7. Thixotropy is most important for which of the following dosage forms?

• Suspensions, gels, and creams
• Tablets for direct compression only
• Dry powder inhalers exclusively
• Solid chewable lozenges

Correct Answer: Suspensions, gels, and creams

Q8. What does recovery time refer to in thixotropic systems?

• Time for viscosity to return toward initial value after shear cessation
• Time required for drug dissolution
• Duration of stability under light exposure
• Time for viscosity to reach zero

Correct Answer: Time for viscosity to return toward initial value after shear cessation

Q9. Which formulation property benefits from thixotropy in topical products?

• Spreadability and ease of application
• Increased melting point
• Reduced drug potency
• Lower pH stability

Correct Answer: Spreadability and ease of application

Q10. How does thixotropy influence syringeability of injectable suspensions?

• Reduces force needed to inject by lowering viscosity under shear
• Increases required injection force permanently
• Makes the suspension Newtonian
• Has no effect on injection

Correct Answer: Reduces force needed to inject by lowering viscosity under shear

Q11. Which polymer is known to produce thixotropic aqueous suspensions used in ophthalmic formulations?

• Xanthan gum
• Starch
• Sucrose
• Calcium carbonate

Correct Answer: Xanthan gum

Q12. In a rheogram, what pattern indicates thixotropy during increasing then decreasing shear?

• A loop where descending curve lies below ascending curve
• Overlapping ascending and descending curves
• A vertical line indicating infinite viscosity
• A descending curve above the ascending curve

Correct Answer: A loop where descending curve lies below ascending curve

Q13. What mechanism primarily explains thixotropy in colloidal gels?

• Shear-induced breakdown of a particle network and slow rebuilding at rest
• Permanent chemical crosslinking under shear
• Rapid evaporation of solvent during shear
• Immediate crystallization of solutes

Correct Answer: Shear-induced breakdown of a particle network and slow rebuilding at rest

Q14. Which factor does NOT typically affect thixotropic behavior?

• Drug’s color
• Temperature
• Shear rate and duration
• Excipients and concentration

Correct Answer: Drug’s color

Q15. Why is thixotropy relevant to oral suspensions?

• Helps maintain homogeneity during storage but allows pourability during dispensing
• Makes suspensions taste better
• Prevents microbial growth completely
• Ensures tablets disintegrate faster

Correct Answer: Helps maintain homogeneity during storage but allows pourability during dispensing

Q16. Which test parameter quantifies the degree of thixotropy?

• Hysteresis loop area from shear-rate sweep
• Melting point depression
• Optical rotation angle
• Infrared absorbance at 1700 cm-1

Correct Answer: Hysteresis loop area from shear-rate sweep

Q17. A formulation shows rapid viscosity recovery immediately after shear stops. This indicates:

• Low thixotropic recovery time and fast structural rebuild
• Rheopexy
• Poor formulation stability
• Irreversible breakdown

Correct Answer: Low thixotropic recovery time and fast structural rebuild

Q18. Which excipient combination can enhance thixotropy in a hydrogel?

• Carbomer plus a neutralizing agent (e.g., triethanolamine)
• Magnesium stearate plus talc
• Sucrose and citric acid only
• Lactose and microcrystalline cellulose

Correct Answer: Carbomer plus a neutralizing agent (e.g., triethanolamine)

Q19. In which way does temperature generally affect thixotropic fluids?

• Higher temperatures often reduce viscosity and can alter recovery kinetics
• Temperature has no effect
• Higher temperatures always increase viscosity
• Only freezing affects thixotropy

Correct Answer: Higher temperatures often reduce viscosity and can alter recovery kinetics

Q20. Which mathematical model is NOT directly used to describe thixotropic time-dependent behavior?

• Michaelis-Menten enzyme kinetics
• Structural kinetic models with a structural parameter
• Thixotropic loop models using hysteresis
• Time-dependent constitutive models (e.g., thixo-elasto-visco-plastic formulations)

Correct Answer: Michaelis-Menten enzyme kinetics

Q21. For quality control, which procedure helps evaluate batch-to-batch consistency of thixotropic gels?

• Performing repeated shear-rate sweeps and comparing hysteresis areas
• Measuring pH only
• Checking tablet hardness
• Measuring absolute zero-shear viscosity only once

Correct Answer: Performing repeated shear-rate sweeps and comparing hysteresis areas

Q22. Thixotropy can improve the patient experience of topical formulations by:

• Reducing runoff after application while allowing easy spreading
• Increasing systemic side effects
• Causing permanent stiffening on skin
• Preventing absorption completely

Correct Answer: Reducing runoff after application while allowing easy spreading

Q23. Which of the following is an example of a thixotropic pharmaceutical product?

• Semi-solid topical gel that becomes fluid on rubbing and firms on rest
• Immediate release tablet that dissolves in water quickly
• Non-thixotropic Newtonian saline solution
• Dry powder capsule

Correct Answer: Semi-solid topical gel that becomes fluid on rubbing and firms on rest

Q24. Which rheological measurement parameter directly measures yield stress, important for thixotropic suspensions?

• Extrapolated stress at zero shear rate from flow curve
• Melting point
• pKa of the drug
• Optical density

Correct Answer: Extrapolated stress at zero shear rate from flow curve

Q25. Which statement best differentiates pseudoplasticity from thixotropy?

• Pseudoplasticity is instantaneous shear-thinning; thixotropy is time-dependent shear-thinning
• Pseudoplasticity increases viscosity with shear, thixotropy decreases it
• They are identical behaviors
• Pseudoplasticity only occurs at low temperatures

Correct Answer: Pseudoplasticity is instantaneous shear-thinning; thixotropy is time-dependent shear-thinning

Q26. Which additive can reduce thixotropy and make a suspension more Newtonian?

• Low molecular weight solvent or surfactant that breaks particle networks
• High concentration of carbomer
• Xanthan gum at high concentration
• Crosslinking agent that strengthens the gel network

Correct Answer: Low molecular weight solvent or surfactant that breaks particle networks

Q27. Why is shear history important when evaluating thixotropic formulations?

• Previous shear affects current structure and observed viscosity
• Shear history changes the chemical identity of the drug
• Shear history only matters for solids
• It determines the color of the formulation

Correct Answer: Previous shear affects current structure and observed viscosity

Q28. Which of the following best describes an ideal thixotropic suspension for oral dosing?

• High viscosity at rest to prevent sedimentation, low viscosity under shear for pouring
• Low viscosity at rest to promote rapid sedimentation
• Permanently low viscosity
• High viscosity under shear and low viscosity at rest

Correct Answer: High viscosity at rest to prevent sedimentation, low viscosity under shear for pouring

Q29. Which measurement sequence is typical to detect thixotropy using a rotational rheometer?

• Increase shear rate stepwise, then decrease shear rate stepwise, record stress or viscosity
• Measure only at one shear rate
• Heat sample to 200°C then cool rapidly
• Perform UV absorbance during shear

Correct Answer: Increase shear rate stepwise, then decrease shear rate stepwise, record stress or viscosity

Q30. Which property of particles in a suspension promotes thixotropic behavior?

• Interparticle attractive forces forming a weak network
• Perfectly spherical non-interacting particles at low concentration
• Complete solubility of particles
• Highly volatile particle surface

Correct Answer: Interparticle attractive forces forming a weak network

Q31. In formulation optimization, how can thixotropy be increased if sedimentation is a problem?

• Add rheology modifiers like xanthan gum or carbomer to build a network
• Increase solvent volatility
• Reduce particle size without changing concentration
• Reduce viscosity at rest

Correct Answer: Add rheology modifiers like xanthan gum or carbomer to build a network

Q32. Which rheological parameter would you monitor to assess long-term stability related to thixotropy?

• Viscosity at low shear and hysteresis loop area over time
• Only the color change of the formulation
• Drug potency by HPLC only
• Particle melting point

Correct Answer: Viscosity at low shear and hysteresis loop area over time

Q33. Which pH-related phenomenon can influence thixotropic gels based on carbomers?

• Neutralization increases polymer ionization causing gelation and thixotropy
• Lowering pH always makes carbomers stronger gels
• pH has no effect on carbomer gels
• Alkaline pH dissolves all polymers instantly

Correct Answer: Neutralization increases polymer ionization causing gelation and thixotropy

Q34. What is the practical implication of reversible thixotropy during packaging and transport?

• Formulation becomes fluid under shaking then rebuilds at rest, reducing leakage and settling risks
• It causes irreversible phase separation
• It increases microbial contamination
• It prevents any flow during transport

Correct Answer: Formulation becomes fluid under shaking then rebuilds at rest, reducing leakage and settling risks

Q35. Which of the following indicates strong thixotropy in a formulation?

• Large hysteresis loop area and slow viscosity recovery
• No change in viscosity with shear
• Immediate recovery to original viscosity on rest
• Complete solidification on shear

Correct Answer: Large hysteresis loop area and slow viscosity recovery

Q36. Which excipient is least likely to contribute to thixotropic structure?

• Sodium chloride at low concentration
• Xanthan gum
• Colloidal silica
• Hydroxypropyl methylcellulose (HPMC)

Correct Answer: Sodium chloride at low concentration

Q37. When designing a topical thixotropic formulation, which test should be included?

• Spreadability and recovery after shear tests
• Only microbial limit testing
• Tablet friability
• Melting range by DSC exclusively

Correct Answer: Spreadability and recovery after shear tests

Q38. Which phrase best describes time-dependence in thixotropy?

• Viscosity change depends on duration of applied shear
• Viscosity is constant regardless of time under shear
• Viscosity depends only on temperature not time
• Viscosity only depends on chemical reactions

Correct Answer: Viscosity change depends on duration of applied shear

Q39. How can particle size distribution influence thixotropy in suspensions?

• Broad distributions may enhance particle packing and network formation, increasing thixotropy
• Particle size has no role in thixotropy
• Smaller particles always eliminate thixotropy
• Only monodisperse large particles cause thixotropy

Correct Answer: Broad distributions may enhance particle packing and network formation, increasing thixotropy

Q40. Which of these is a potential disadvantage of excessive thixotropy in formulations?

• Slow recovery causing difficulty in re-establishing viscosity after dispensing
• Improved syringeability
• Better suspension stability always
• Faster dissolution of tablet cores

Correct Answer: Slow recovery causing difficulty in re-establishing viscosity after dispensing

Q41. In cosmetics, thixotropic rheology is utilized to:

• Ensure product sits on skin without running but applies smoothly on rubbing
• Increase systemic drug absorption dangerously
• Make the product solid at room temperature
• Eliminate need for preservatives

Correct Answer: Ensure product sits on skin without running but applies smoothly on rubbing

Q42. Which test condition must be controlled strictly when comparing thixotropy across samples?

• Temperature, shear history and measurement geometry
• Sample color only
• Only the batch number
• Evaporation rate at 100°C

Correct Answer: Temperature, shear history and measurement geometry

Q43. What role do surfactants play in thixotropic suspensions?

• They can disrupt or stabilize particle networks altering thixotropy depending on type and concentration
• They always increase thixotropy
• They have no effect on rheology
• They convert suspensions into powders

Correct Answer: They can disrupt or stabilize particle networks altering thixotropy depending on type and concentration

Q44. Which property of a polymer increases its ability to form thixotropic gels?

• High molecular weight and chain entanglement with potential crosslinking
• Very low molecular weight and full solubility without interaction
• Complete hydrophobicity without interaction
• Volatility under ambient conditions

Correct Answer: High molecular weight and chain entanglement with potential crosslinking

Q45. How is thixotropy evaluated during accelerated stability testing?

• Monitoring changes in viscosity and hysteresis over time at elevated temperatures and stresses
• Only checking pH once at start
• Freezing samples and measuring hardness
• Measuring absorbance at 280 nm only

Correct Answer: Monitoring changes in viscosity and hysteresis over time at elevated temperatures and stresses

Q46. Which of the following best describes a thixotropic recovery curve?

• Viscosity plotted versus time after removal of shear showing gradual recovery
• Immediate jump back to original viscosity
• Linear decrease in viscosity with time at rest
• No change in viscosity during recovery

Correct Answer: Viscosity plotted versus time after removal of shear showing gradual recovery

Q47. Which excipient could be used as a particulate rheology modifier to impart thixotropy?

• Colloidal silica (fumed silica)
• Sucrose syrup
• Magnesium chloride solution only
• Pure ethanol

Correct Answer: Colloidal silica (fumed silica)

Q48. During formulation, controlling ionic strength can influence thixotropy by:

• Shielding or enhancing electrostatic interactions between particles or polymer chains
• Only changing color
• Activating covalent bonding permanently
• Having no measurable effect

Correct Answer: Shielding or enhancing electrostatic interactions between particles or polymer chains

Q49. Which concept is crucial when predicting in vivo performance influenced by thixotropy?

• How shear in administration or application changes drug release and residence time
• The melting point of the drug only
• Color stability under light only
• Hygroscopicity of packaging material only

Correct Answer: How shear in administration or application changes drug release and residence time

Q50. For an oral suspension that displays thixotropy, what instruction should be given to patients?

• Shake gently before use to redisperse particles, then pour (allow short rest if necessary)
• Do not shake under any circumstances
• Freeze before use
• Only use with a tablet cutter

Correct Answer: Shake gently before use to redisperse particles, then pour (allow short rest if necessary)

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

Mail- Sachin@pharmacyfreak.com