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Gary's lecture (Pharmaceutics) > Dissolution > Flashcards

Dissolution Flashcards

1
Q

Why are fewer new medicines increasingly available?

A

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

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2
Q

What does dissolution refer to?

A

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

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3
Q

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?

A

TRUE

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4
Q

What are solutions?

A

They are a homogenous mixture of two or more pure substances

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5
Q

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

A

FALSE

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6
Q

How does a solid dissolve into a liquid?

A

Electrostatic in nature

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7
Q

What drives the dissolution process?

A

Water molecules are electrically neutral

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8
Q

What are the enegetics of this process?

A

Thermodynamics (heating)

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9
Q

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?

A

TRUE

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10
Q

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

A

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

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11
Q

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

A

Non polar solvents e.g oils

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12
Q

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

A

TRUE

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13
Q

How does a solution form?

A
  • 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)
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14
Q

What is a saturated solution?

A
  • 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
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15
Q

What is an unsaturated solution (sub-saturated)?

A
  • contains less than the maximum possible amount of solute at a specific temp
  • There is no excess solid present in the vessel
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16
Q

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

A

FALSE

17
Q

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

A

TRUE

18
Q

Descibe the mechanism of dissolution?

A
  • 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
19
Q

What is the dissolution boundary layer?

A

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

20
Q

What is dissolution depend on?

A
  • The slowest or rate limiting step of the process governed by ficks first law
21
Q

What does the Noyes and whitney equation describe?

A

The rate of dissolution of a solid in a liquid

22
Q

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?

A

TRUE

23
Q

What does the diffusion coefficient consider?

A
  • How temp affects the diffusion coeffcient

- How Viscosity affects diffusion coefficient

24
Q

What is dissolution rate affected by?

A

Temp and viscosity

25
Q

What is sink conditions?

A

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

26
Q

What are the factors affecting dissolution?

A
  • 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
27
Q

What is the common ion effect?

A

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

28
Q

What biological factors affect dissolution?

A
  • 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
29
Q

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

A

TRUE

30
Q

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

A

TRUE

31
Q

What is henry’s law?

A

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

Gary's lecture (Pharmaceutics) (7 decks)

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