Dissolution and Release

Question 1

What is dissolution?

Answer 1

The process by which a solid phase goes into a solution phase through interaction with a solvent

Question 2

Why is dissolution important

Answer 2

Solid oral dosage forms must be able to be dissolved to release the active drug

Question 3

What does the Noyes-Whitney equation describe?

Answer 3

The dissolution rate of a solid in relation to the properties of the solid and the dissolution medium

Question 4

What is the driving force of dissolution?

Answer 4

Concentration gradient

Question 5

What are sink conditions?

Answer 5

When the concentration of a solid is less than its solubility

Question 6

What is the order of the Noyes-Whitney equation?

Answer 6

First order kinetics

Question 7

What is the order of reaction under sink conditions?

Answer 7

Zero order kinetics

Question 8

What is the Hixson-Crowell Cube Root Law?

Answer 8

The dissolution rate of uniformly sized drug particles can be expressed based on the cube root of the weight of the particles

Question 9

What are the two methods of dissolution testing?

Answer 9

Basket assembly and Paddle method

Question 10

What are the advantages of basket testing?

Answer 10

• Useful for low density products that may float

- Formulations can be transferred form one vessel to another

Question 11

What are the advantages of paddle testing?

Answer 11

• Floating formulations may be held down

- Practical for powder dissolution studies

Question 12

What are the parameters for dissolution apparatuses?

Answer 12

• 50-150 RPM
• 37oC
• Volume 500-900mL

Question 13

What is drug release?

Answer 13

The process by which a drug leaves a formulation and is subject to absorption

Question 14

What factors affect rate of release?

Answer 14

Physicochemical properties of the drug (size, shape, pKa)

Physiological properties of the biological system (temp, pH, enzymes)

Question 15

What factors affect the Higuchi equation?

Answer 15

Amount of drug in matrix
Diffusion coefficient
Solubility of drug in matrix
Depletion zone

Question 16

What is the Higuchi equation?

Answer 16

Describes drug release from a matrix system

Question 17

What are the assumptions for the Higuchi equation?

Answer 17

Initial drug concentration in the matrix is higher than drug solubility
Diffusion occurs in one direction
Diffusion is Constant
Perfect sink

Question 18

What is the Korsmeyer-Peppas equation?

Answer 18

Classifies mode of drug release from polymeric systems

Question 19

What happens in the KP equaiton when n = 0.45?

Answer 19

Fickian diffusion, can be described by Fick’s Law

Question 20

0.45 < n < 0.89

Answer 20

Anomalous transport, combination of diffusion and matrix erosion

Question 21

n = 0.89

Answer 21

Drug release is controlled by matrix erosion

Question 22

Why do we modify drug release?

Answer 22

• Delayed release
• Repeated action
• Prolonged release

Question 23

What are the three steps of drug release from matrices?

Answer 23

1) Surrounding liquid -> matrix
2) Dissolution of drug in liquid
3) Drug leaches out through pores