Diffusion, dissolution, PK parameters MCQs With Answer

Diffusion, dissolution, PK parameters MCQs With Answer

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Diffusion, dissolution, and pharmacokinetic (PK) parameters form the foundation for designing and optimizing modern dosage forms and delivery systems in M. Pharm curricula. This blog provides a concise yet rigorous set of MCQs to test and strengthen your understanding of key concepts such as Fickian diffusion, Noyes–Whitney dissolution, matrix release kinetics, IVIVC, noncompartmental analysis, and core PK relationships among clearance, volume of distribution, and half-life. Each question reflects practical problem-solving and interpretation skills expected in Modern Pharmaceutics (MPH 103T), helping you connect theory to formulation and in vivo performance. Use these MCQs to self-assess, revise critical equations, and refine your reasoning for exams and research applications.

Q1. Which equation best describes steady-state flux across a membrane driven by a concentration gradient?

  • Fick’s first law: J = −D (dC/dx)
  • Fick’s second law: ∂C/∂t = D (∂²C/∂x²)
  • Noyes–Whitney equation: dC/dt = (D·A/h)(Cs − C)
  • Stokes–Einstein relation: D = kT/(6π η r)

Correct Answer: Fick’s first law: J = −D (dC/dx)

Q2. The permeability coefficient (P) of a drug through a polymeric membrane is best represented by which relationship?

  • P = D·h/K
  • P = (D·K)/h
  • P = h/(D·K)
  • P = K/(D·h)

Correct Answer: P = (D·K)/h

Q3. The Noyes–Whitney equation for dissolution rate can be written as:

  • dC/dt = k0
  • dC/dt = (D·A/h)(Cs − C)
  • dC/dt = k·C
  • dC/dt = (K·h/D)(C − Cs)

Correct Answer: dC/dt = (D·A/h)(Cs − C)

Q4. In dissolution testing, “sink conditions” most appropriately mean:

  • The dissolved drug concentration remains at or above saturation (C ≥ Cs)
  • The dissolved drug concentration is less than 10% of saturation (C ≤ 0.1·Cs)
  • The diffusion layer thickness (h) is zero
  • The agitation speed is maintained below 50 rpm

Correct Answer: The dissolved drug concentration is less than 10% of saturation (C ≤ 0.1·Cs)

Q5. A hallmark of diffusion-controlled release from a planar matrix (Higuchi model) is:

  • Zero-order release independent of time
  • First-order release proportional to the amount remaining
  • Linear relationship between cumulative amount released and square root of time
  • Exponential increase in release rate over time

Correct Answer: Linear relationship between cumulative amount released and square root of time

Q6. The Hixson–Crowell cube-root law is most applicable when:

  • Drug diffusion through a non-eroding matrix dominates release
  • Surface area and particle size change during dissolution
  • Dissolution is surface-reaction limited with constant area
  • Release is governed by erosion-only mechanisms

Correct Answer: Surface area and particle size change during dissolution

Q7. According to the Stokes–Einstein relation, the diffusion coefficient (D) varies with which proportionality?

  • D ∝ η·r/T
  • D ∝ T/(η·r)
  • D ∝ 1/T
  • D is independent of temperature and viscosity

Correct Answer: D ∝ T/(η·r)

Q8. In the Biopharmaceutics Classification System (BCS), the rate-limiting step for oral absorption of a Class II drug is typically:

  • Intestinal permeability
  • Dissolution
  • Gastric emptying
  • First-pass metabolism

Correct Answer: Dissolution

Q9. A drug has CL = 5 L/h and Vd = 50 L (IV). Its elimination half-life (t½) is approximately:

  • 0.69 h
  • 5.0 h
  • 6.9 h
  • 10.0 h

Correct Answer: 6.9 h

Q10. In noncompartmental analysis, a 100 mg IV bolus dose yields AUC(0–∞) = 25 mg·h/L. The systemic clearance (CL) is:

  • 2.5 L/h
  • 4 L/h
  • 12.5 L/h
  • 25 L/h

Correct Answer: 4 L/h

Q11. A Level A IVIVC is best defined as:

  • A rank order correlation between in vitro dissolution and Cmax
  • A point-to-point relationship between in vitro dissolution and in vivo input rate/absorption
  • A correlation only between percentage dissolved at single time point and AUC
  • A relationship specific to immediate-release products only

Correct Answer: A point-to-point relationship between in vitro dissolution and in vivo input rate/absorption

Q12. Flip-flop kinetics after extravascular dosing occurs when:

  • ka ≫ ke and terminal slope reflects elimination
  • ka ≪ ke and terminal slope reflects absorption
  • Bioavailability is zero
  • The drug follows zero-order elimination

Correct Answer: ka ≪ ke and terminal slope reflects absorption

Q13. To estimate fraction absorbed from plasma data after a single oral dose in a one-compartment model with first-order absorption, the appropriate method is:

  • Loo–Riegelman method
  • Wagner–Nelson method
  • Feathering (method of residuals) only
  • Moment analysis only

Correct Answer: Wagner–Nelson method

Q14. According to the Noyes–Whitney framework, reducing particle size generally increases dissolution rate primarily by:

  • Increasing saturation solubility (Cs)
  • Decreasing diffusion coefficient (D)
  • Increasing effective surface area (A)
  • Increasing diffusion layer thickness (h)

Correct Answer: Increasing effective surface area (A)

Q15. A dosage form designed to deliver drug at an approximately constant rate (zero-order) throughout most of its life is typically:

  • A matrix tablet following Higuchi kinetics
  • An osmotic-controlled system (e.g., elementary osmotic pump)
  • A disintegrating immediate-release tablet
  • A spherical pellet exhibiting Hixson–Crowell kinetics

Correct Answer: An osmotic-controlled system (e.g., elementary osmotic pump)

Q16. In dissolution testing, increasing agitation speed usually:

  • Increases diffusion layer thickness (h), decreasing dissolution rate
  • Decreases diffusion layer thickness (h), increasing dissolution rate
  • Has no effect on the boundary layer or dissolution rate
  • Decreases saturation solubility (Cs), lowering dissolution rate

Correct Answer: Decreases diffusion layer thickness (h), increasing dissolution rate

Q17. For a high hepatic extraction ratio drug administered IV, systemic clearance (assuming hepatic elimination predominates) is best described as:

  • Capacity-limited and independent of hepatic blood flow
  • Flow-limited and approximating hepatic blood flow
  • Determined solely by fraction unbound in plasma (fu)
  • Equal to Vd multiplied by ke

Correct Answer: Flow-limited and approximating hepatic blood flow

Q18. A very large apparent volume of distribution (Vd » total body water) most likely indicates:

  • Extensive plasma protein binding with minimal tissue uptake
  • Extensive tissue binding or partitioning outside plasma
  • Restricted distribution confined to vascular space
  • Zero-order elimination kinetics

Correct Answer: Extensive tissue binding or partitioning outside plasma

Q19. In moment analysis, mean residence time (MRT) after IV bolus is calculated as:

  • MRT = AUC/AUMC
  • MRT = AUMC/AUC
  • MRT = Vd/CL only for two-compartment models
  • MRT = 0.693/ke

Correct Answer: MRT = AUMC/AUC

Q20. A planar membrane (h = 100 µm = 0.01 cm) with D = 1×10⁻⁶ cm²/s and K = 1 separates donor and receiver phases with ΔC = 1 mg/cm³. The steady-state flux (J) is approximately:

  • 1×10⁻² mg/(cm²·s)
  • 1×10⁻⁴ mg/(cm²·s)
  • 1×10⁻⁶ mg/(cm²·s)
  • 1×10⁻⁸ mg/(cm²·s)

Correct Answer: 1×10⁻⁴ mg/(cm²·s)

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