Dissolution

Question 1

Why are fewer new medicines increasingly available?

Answer 1

Increasing in phase 1 and 2 candidates is not always passed through to phase 3

Question 2

What does dissolution refer to?

Answer 2

The process by which a drug molecule moves from solid phase to the liquid phase

Question 3

If a drug has low solubility in the body dissolution may be the rate limiting step to absorption and thereafter, therapeutic effect. TRUE OR FALSE?

Answer 3

TRUE

Question 4

What are solutions?

Answer 4

They are a homogenous mixture of two or more pure substances

Question 5

In a solution, the solute is not dispersed uniformly thoughout the solvent. TRUE OR FALSE?

Answer 5

FALSE

Question 6

How does a solid dissolve into a liquid?

Answer 6

Electrostatic in nature

Question 7

What drives the dissolution process?

Answer 7

Water molecules are electrically neutral

Question 8

What are the enegetics of this process?

Answer 8

Thermodynamics (heating)

Question 9

If the intermolecular forces between solute and solvent are stronger it is more likely that the solute will dissolve in the solvent. TRUE OR FALSE?

Answer 9

TRUE

Question 10

What type of intermolecular forces may occur between solute and solvent?

Answer 10

Hydrogen bonds
Dipole-dipole
Van der waals (for ionic species)

Question 11

What are vitamins A,D, K and E soluble in?

Answer 11

Non polar solvents e.g oils

Question 12

Vitamin B and C are water soluble. TRUE OR FALSE?

Answer 12

TRUE

Question 13

How does a solution form?

Answer 13

• Solvent molecules are attracted to surface ions
• Each ion is surrounded by solvent molecules
• Energy results in solvation/ hydration (e.g an ionic solid dissolving in water)

Question 14

What is a saturated solution?

Answer 14

• Solvent holds as much solute as possible at a particular temperature, the undissolved solid remians in the vessel as a sediment
• Dissolved solute is in dynamic equilbrium with the solid solute particles

Question 15

What is an unsaturated solution (sub-saturated)?

Answer 15

• contains less than the maximum possible amount of solute at a specific temp
• There is no excess solid present in the vessel

Question 16

Solvents do not hold more solvent than normally possible at a specific temp. TRUE OR FALSE?

Answer 16

FALSE

Question 17

Supersaturated solutions are unstable and often result in crystallisation, the opposite of solvation. TRUE OR FALSE?

Answer 17

TRUE

Question 18

Descibe the mechanism of dissolution?

Answer 18

• It is an interfacial reaction (which results in liberation of a solute molecule from solid phase/the solution in contact with the solid will become saturated)
• Solute molecules migrates through the boundary layers surrounding the solid to the bulk solution
• The boundary layer is predominately static and surrounds the wetted surface of the solid
• Mass transfer occurs slowly through the boundary layer to the bulk solution
• Reaction must be energetically favourable

Question 19

What is the dissolution boundary layer?

Answer 19

-A thin layer of solution in contact with the solid (i.e dosage form)

Question 20

What is dissolution depend on?

Answer 20

• The slowest or rate limiting step of the process governed by ficks first law

Question 21

What does the Noyes and whitney equation describe?

Answer 21

The rate of dissolution of a solid in a liquid

Question 22

If C is significantly smaller than Cs, the system is said to be at sink condition allowing the equation to be simplified. TRUE OR FALSE?

Answer 22

TRUE

Question 23

What does the diffusion coefficient consider?

Answer 23

• How temp affects the diffusion coeffcient

- How Viscosity affects diffusion coefficient

Question 24

What is dissolution rate affected by?

Answer 24

Temp and viscosity

Question 25

What is sink conditions?

Answer 25

-usually when the bulk concentration is significantly lower than the concentration in the boundary layer

Question 26

What are the factors affecting dissolution?

Answer 26

- Surface area - larger SA higher dissolution rate/particle size and porosity - Solubility - particle size (solubility increases when particle size is reduced)/ temp solubility increases when temp is increased - Solvent choice - co-solvents may alter solubility of drugs - Structure of the drug molecule - weak acid/base/hydrophilic - Polymorphism - different solid states - Thickness of boundary layer

Question 27

What is the common ion effect?

Answer 27

-the solubility of one salt is reduced by the presence of another having a common ion

Question 28

What biological factors affect dissolution?

Answer 28

- Viscosity of fluid in the GI tract may be increased by food (this may reduce dissolution rate) - Dissolution increases due to the presence and activity of surfactants and bile salts in the gastric fluid - Gastric motility can reduce the size of the diffusion layer - Gastric pH is acidic - dissolution of weak acids will increase dissolution in the stomach

Question 29

Polar liquids will dissolve in polar solvents (like dissolves like) due to hydrogen and dipole-dipole interactions. TRUE OR FALSE?

Answer 29

TRUE

Question 30

Increasing the pressure in a system will significanlty increase the solubility of dissolved gases. TRUE OR FALSE?

Answer 30

TRUE

Question 31

What is henry's law?

Answer 31

The amount of a gas dissolved in a solution is directly proportional to the pressure of the gas above the solution