Dissolution Testing Models MCQs With Answer

Dissolution Testing Models MCQs With Answer

Introduction: Dissolution testing is a cornerstone of formulation development, quality control, and biopharmaceutics. This set of MCQs focuses on common dissolution models (e.g., Noyes–Whitney, Higuchi, Korsmeyer–Peppas, Weibull, Hixson–Crowell), model selection, parameters (DE, MDT, f2), experimental conditions (sink, apparatus) and data analysis (linearization vs non‑linear regression, AIC). The questions are designed to deepen understanding of mechanisms, assumptions, limitations and practical applications in M.Pharm formulation development. Use these to test concept mastery, reinforce model interpretations, and prepare for exams or research in dissolution method design and IVIVC considerations.

Q1. What is the primary purpose of dissolution testing in pharmaceutical formulation development?

• To measure the stability of the solid drug substance under humidity
• To determine the rate and extent of drug release for quality control and IVIVC
• To assess the potency of drug by chromatographic methods
• To evaluate the tablet hardness and friability only

Correct Answer: To determine the rate and extent of drug release for quality control and IVIVC

Q2. The Noyes–Whitney equation states that the dissolution rate is proportional to which combination of factors?

• The partition coefficient and melting point
• Surface area, diffusion coefficient, concentration gradient (Cs – C), and inverse of diffusion layer thickness
• Disintegration time and tablet porosity only
• Log P and pKa value only

Correct Answer: Surface area, diffusion coefficient, concentration gradient (Cs – C), and inverse of diffusion layer thickness

Q3. Which statement correctly describes the key assumption and mathematical form of the Higuchi model?

• It assumes constant surface area and predicts cumulative release is proportional to time
• It models erosion-controlled systems where cube root of remaining mass is linear with time
• It assumes a homogeneous matrix and predicts cumulative amount released is proportional to square root of time
• It is an empirical sigmoidal model with a shape parameter beta

Correct Answer: It assumes a homogeneous matrix and predicts cumulative amount released is proportional to square root of time

Q4. In the Korsmeyer–Peppas model applied to a cylindrical matrix tablet, a release exponent n value between 0.45 and 0.89 indicates which mechanism?

• Pure Fickian diffusion
• Case II transport (zero‑order polymer relaxation controlled)
• Anomalous (non‑Fickian) transport with combined diffusion and erosion
• Immediate dissolution with no mechanistic relevance

Correct Answer: Anomalous (non‑Fickian) transport with combined diffusion and erosion

Q5. The Weibull model includes a shape parameter (β). What does β > 1 typically indicate about the dissolution profile?

• Pure first‑order exponential decay
• Delayed onset or sigmoidal release with an initial lag phase
• Instantaneous release reaching 100% at t=0
• Linear zero‑order release

Correct Answer: Delayed onset or sigmoidal release with an initial lag phase

Q6. The Hixson–Crowell cube‑root law is most appropriate for which situation?

• Describing diffusion from a planar matrix where area is constant
• Describing dissolution when drug particles erode but maintain their geometric shape, so cube root of mass decreases linearly with time
• Modeling release exclusively from lipid‑based emulsions
• Predicting solubility changes due to pH shifts

Correct Answer: Describing dissolution when drug particles erode but maintain their geometric shape, so cube root of mass decreases linearly with time

Q7. Dissolution efficiency (DE) is best described as which of the following?

• The time to reach 50% dissolution
• The area under the dissolution curve up to a certain time expressed as a percentage of the area of a rectangle representing 100% dissolution in the same time
• The slope of the log cumulative percentage dissolved vs log time plot
• The maximum concentration achieved in the dissolution medium

Correct Answer: The area under the dissolution curve up to a certain time expressed as a percentage of the area of a rectangle representing 100% dissolution in the same time

Q8. According to regulatory guidance, two dissolution profiles are considered similar when the similarity factor f2 lies within which range?

• 10–30
• 30–49
• 50–100
• 101–150

Correct Answer: 50–100

Q9. What defines appropriate “sink conditions” in dissolution testing?

• The dissolved drug concentration is equal to the saturation solubility
• The dissolution medium volume is less than tablet volume
• The dissolved drug concentration remains well below saturation, commonly less than about 10% of drug solubility in the medium
• The paddle speed is high enough to prevent any dissolution

Correct Answer: The dissolved drug concentration remains well below saturation, commonly less than about 10% of drug solubility in the medium

Q10. Intrinsic dissolution rate (IDR) is defined as:

• Dissolution rate normalized to tablet weight under variable surface area
• Dissolution rate per unit surface area under constant surface area and specified hydrodynamic conditions
• Total percentage dissolved at 60 minutes
• Rate constant from a first‑order fit of cumulative dissolution

Correct Answer: Dissolution rate per unit surface area under constant surface area and specified hydrodynamic conditions

Q11. Which USP dissolution apparatus is a flow‑through cell particularly suitable for poorly soluble drugs and IVIVC studies?

• Apparatus I (rotating basket)
• Apparatus II (paddle)
• Apparatus III (reciprocating cylinder)
• Apparatus IV (flow‑through cell)

Correct Answer: Apparatus IV (flow‑through cell)

Q12. When comparing model fits to dissolution data, the Akaike Information Criterion (AIC) is used to:

• Always select the model with the most parameters
• Provide a goodness‑of‑fit statistic that penalizes model complexity; lower AIC indicates a better balance of fit and parsimony
• Measure only the residual variance without penalty for complexity
• Convert dissolution data into normalized fractional release

Correct Answer: Provide a goodness‑of‑fit statistic that penalizes model complexity; lower AIC indicates a better balance of fit and parsimony

Q13. Which is a key advantage of non‑linear regression over linearization for fitting dissolution models?

• Non‑linear regression requires data transformation that eliminates heteroscedasticity
• Non‑linear regression avoids bias introduced by transforming data and provides parameter estimates on the original scale
• Linearization always provides more accurate parameter errors
• Non‑linear regression cannot handle complex models

Correct Answer: Non‑linear regression avoids bias introduced by transforming data and provides parameter estimates on the original scale

Q14. The discriminatory power of a dissolution method refers to:

• Its ability to measure absolute drug potency
• Its capacity to detect relevant changes in formulation or manufacturing that affect release
• How fast the apparatus runs tests
• The solubility of an API in the chosen medium

Correct Answer: Its capacity to detect relevant changes in formulation or manufacturing that affect release

Q15. Which description best distinguishes USP Apparatus I (basket) from Apparatus II (paddle)?

• Apparatus I uses a rotating basket that encloses the dosage form; Apparatus II uses a paddle that stirs freely above the dosage form
• Apparatus I is a flow‑through cell; Apparatus II is a reciprocating cylinder
• Both apparatuses are identical in hydrodynamics and interchangeable for all products
• Apparatus I measures intrinsic dissolution; Apparatus II measures only disintegration

Correct Answer: Apparatus I uses a rotating basket that encloses the dosage form; Apparatus II uses a paddle that stirs freely above the dosage form

Q16. According to Noyes–Whitney, which experimental change would most likely decrease the dissolution rate?

• Decreasing diffusion layer thickness
• Increasing surface area (e.g., finer particle size)
• Reducing the diffusion coefficient
• Increasing saturation solubility through surfactant addition

Correct Answer: Reducing the diffusion coefficient

Q17. Zero‑order release kinetics from a dosage form implies which of the following?

• Cumulative amount released increases linearly with the square root of time
• Cumulative amount released is constant per unit time (linear amount vs time), ideal for controlled release
• Log of percent remaining is linear with time
• Release rate is proportional to the remaining drug amount (concentration dependent)

Correct Answer: Cumulative amount released is constant per unit time (linear amount vs time), ideal for controlled release

Q18. Mean dissolution time (MDT) is interpreted as:

• The variance of dissolution measurements at t=0
• A statistical measure of the time for drug release; smaller MDT indicates faster release
• The time to reach maximum concentration in plasma
• The dissolution medium pH at which solubility is maximal

Correct Answer: A statistical measure of the time for drug release; smaller MDT indicates faster release

Q19. When applying the Korsmeyer–Peppas model it is common practice to fit the model to which portion of the dissolution curve?

• The entire curve including tailing after 95% release
• Only the initial 5% of release
• Typically up to about 60% cumulative release where the power‑law approximation holds
• Only data points after 80% release

Correct Answer: Typically up to about 60% cumulative release where the power‑law approximation holds

Q20. A good model validation for dissolution data should show which characteristic in residual analysis?

• Systematic pattern (e.g., increasing residuals with time)
• Nonrandom clustering at early time points only
• Randomly distributed residuals with no obvious pattern and approximately constant variance
• Residuals always equal zero for a valid model

Correct Answer: Randomly distributed residuals with no obvious pattern and approximately constant variance

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