# Drug Biotechnology Questions and Answers – Physicochemical Factors Affecting Drug Absorption

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This set of Tricky Drug Biotechnology Questions and Answers focuses on “Physicochemical Factors Affecting Drug Absorption”.

1. Which one of the following is a critical rate-limiting step of drug absorption?
a) Rate of drug disintegration
b) Size of the drug
c) Size of the porous particle
d) Rate of dissolution

Explanation: For orally administered drug, the two critically slower rate determining step is the rate of dissolution and the rate of drug permeation. Dissolution is the rate determining stem for poorly aqueous soluble drugs and hydrophobic drugs.

2. Which sentence will define the Dissolution rate?
a) Amount of solid substrate that goes into solution under constant time
b) Amount of solid substrate that goes into solution under constant time under standard temperature
c) Amount of solid substrate that goes into solution under constant time under standard temperature, pH, and pressure
d) Amount of solid substrate that goes into solution under constant time under standard temperature, pH, solvent composition and constant surface area

Explanation: Dissolution rate is defined as the amount of solid substrate that goes into solution under constant time under standard temperature, pH, solvent composition and constant surface area. It is a dynamic process. Drugs having poor aqueous solubility have less dissolution rate.

3. What should be the ideal solubility rate of an orally administered drug in the pH range of 2 to 8?
a) 3-4mg/ml
b) 4-6 mg/ml
c) 7-8 mg/ml
d) 1-2 mg/ml

Explanation: The solubility of any orally administered drug should be between 1-2 mg/ml in the range of pH 2-8. The solubility becomes a great matter of concern if it is less than that. And if more than that the dosage must be carefully calculated.

4. Which one of these is not a theory of Drug dissolution?
a) Diffusion layer model
b) Fick’s law of diffusion
c) Penetration or surface renewal theory
d) Interfacial barrier model

Explanation: Fick’s law of diffusion states that drug molecules diffuse from higher concentration to lower concentration until equilibrium is reached. Theories of drug dissolution are Diffusion layer model or Fil theory, Danckwert’s model or Penetration or surface renewal theory, Interfacial barrier model or Double barrier theory.

5. Which theory takes into account that a thin film is created by the solution of the solid at the solid-liquid interface?
a) Interfacial barrier model
b) Diffusion layer model
c) Penetration or surface renewal theory
d) Danckwert’s model

Explanation: Diffusion layer model states that solution of a solid form a thin film or layer at the solid-liquid interface which is called as the stagnant film or diffusion layer which gets saturated with the drug. This step is rapid.

6. In the equation G=Ki (Cs-Cb), what does G stands for______________
a) Dissolution rate per unit area
b) Effective interfacial transport constant
c) Concentration of the solute
d) Concentration of the impurity

Explanation: According to the interfacial barrier model, an intermediate concentration exists at the interface which is a result of the solvation mechanism and is a function of solubility. Here in the equation G stands for dissolution rate per unit area, Ki stands for effective interfacial transport constant.

7. Which model does not approve the existence of the stagnant layer in the solid-liquid interface?
a) Interfacial barrier model
b) Diffusion layer model
c) Penetration or surface renewal theory
d) Danckwert’s model

Explanation: Danckwert did not approve the existence of the stagnant layer and suggested that turbulence in the dissolution medium exists at the solid/liquid interface. Due to which the agitated fluid consists of a macroscopic mass of eddies or packets reach the solid-liquid interface due to the eddy currents, absorb the solute by diffusion and carry it to the bulk of the solution.

8. What does the interfacial barrier model states?
a) An intermediate concentration exists at the interface
b) Turbulence in the dissolution medium exists at the solid/liquid interface
c) Formation a thin film or layer at the solid-liquid interface
d) Solutes passes easily through the interfaces

Explanation: An intermediate layer exist at the interface of the solid and liquid layers. This intermediate layer holds and intermediate concentration at the interface which results is solvation mechanism. The theory does not talk about any turbulence, or presence of solutes.

9. In the equation, Wo1/3-W1/3=Kt, K stands for ____________
a) The original mass of the drug
b) Mass of the drug remaining after time t
c) Dissolution constant
d) Concentration of solute

Explanation: To calculate the particle size decrease and change in the surface area of the dissolution Hixson and Crowell’s cubit root law of dissolution is followed, Wo1/3-W1/3=Kt, where, Wo stands for original mass of the drug, W stands for the mass of the drug remaining after time t, K stands for dissolution constant.

10. Which are the two rate-determining step of drug absorption when given orally?
a) Disintegration and deaggregation
b) Disintegration and Dissolution
c) Dissolution and permeation through the membrane
d) Permeation through the membrane and Disintegration

Explanation: The two critical slower rate-determining processes in the absorption of orally administered drugs are the rate of dissolution and rate of the solute or the drug permeation through the cell membrane or biomembrane.

11. The maximum amount of solute dissolved in a given solvent under standard conditions of temperature, pressure, and pH is known as __________
a) Dissolution rate
b) Intrinsic dissolution
c) Rate limiting step
d) Absolute or intrinsic solubility

Explanation: Absolute or intrinsic solubility is defined as the maximum amount of solute dissolved in a given solvent under standard conditions of temperature, pressure, and pH. It is a static property. Dissolution rate is the amount of a solid substance that dissolves into solution under given conditions.

12. In the equation, V dC/dt = dm/dt = A(Cs-Cb).√ γ D, what does γ stands for?
a) Mass of the solid dissolved
b) Rate of surface renewal
c) Concentration of solute
d) Concentration of the drug

Explanation: The Danckwert’s model is expressed by the equation, V dC/dt = dm/dt = A (Cs-Cb).√ γ D, where γ is the rate of surface renewal, m is the mass of solid dissolved. Cs concentration of the solute.

13. Each face of the crystal has a different interfacial barrier.
a) True
b) False 