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Pharm Y2S2 Medicine > Pre-formulation considerations > Flashcards

Pre-formulation considerations Flashcards

1
Q

What is the purpose of excipients?

A

They are used to optimise drug design

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2
Q

What does the choice of dosage form depend on?

A

The use of the drug

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3
Q

What are the principle objectives to achieve?

A
  • predictable therapeutic response
  • product suitable for large scale manufacture
  • reproducible product quality
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4
Q

What dosage form does prednisolone come in?

A
  • tablet
  • injections
  • eye drops
  • enema
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5
Q

What factor should be considered in pre-formulation?

A
  • biopharmaceutical
  • physiochemical properties
  • therapeutic
  • financial
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6
Q

Why should biopharmaceutical factors be considered?

A

Biological effect might influence the dosage form.

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7
Q

What is pre-formulation?

A

A pilot study to enable you to optimise drug formulation

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8
Q

What properties of the drug are looked at?

A

Physiochemical properties

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9
Q

What factors determine bioavailability?

A
  • stability
  • dissolution
  • interaction
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10
Q

What are the techniques used in physicochemical analysis?

A
  • UV spectroscopy
  • HPLC
  • Differential scanning calorimetry (DSC)
  • Dynamic vapour sorption (DVS)
  • Xray powder diffraction (XRPD)
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11
Q

What molecular / intrinsic properties of the drug can’t be changed unless the structure is chemically modified?

A
  • Solubuility
  • stability
  • hygroscopicity
  • pKa
  • partition coefficient
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12
Q

What does the solubility of a drug need to be when used in animal studies?

A

> 1mg/1ml

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13
Q

What should the solubility of the final product be?

A

10mg/1ml

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14
Q

Define hygroscopicity

A

the ability of a substance to attract water

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15
Q

What can adsorption or absorption cause?

A

It can cause changes in physiochemical properties of the drug affecting:

  • powder flow
  • drying
  • ease of compact
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16
Q

What happens to amorphous substances when they interact with water?

A

they breakdown faster leading to molecular mobility or crystallisation

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17
Q

What kind of molecules have a greater tendency to absorb water?

A

Salts - this causes problems with dissolution

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18
Q

What do KCl and Mg(OH)2 do in the presence of water?

A

They are very hygroscopic - dissolve spontaneously to form solutions (deliquescence)

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19
Q

Define adsorption

A

adhesions of atoms, ions or molecules on to a surface

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20
Q

What happens when adsorption occurs on the surface?

A

small layers form which stop the drug from dissolving.

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21
Q

What do microporous surfaces do?

A

allow water into capillary spaces within the solid

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22
Q

Give an example of a microporous substance

A

Silica gel

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23
Q

How is water uptake determined?

A

By measuring a change in mass

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24
Q

What is Thermogravimetric analysis (TGA)?

A

The process of heating up a mass, and measuring how much water is absorbed by how light it is after heating.

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25
Q

What is dynamic vapour sorption?

A

Measuring a substance then introducing humidity and measure its mass after. The weight gain will tell how much has been absorbed.

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26
Q

What are macroscopic/bulk properties?

A

These can be intermolecular interactions, solid state form, shape and environment

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27
Q

What make up macroscopic properties?

A
  • Melting point
  • Enthalpy of fusion
  • Physical form
  • Particle size and shape
  • Density
  • Particle flow
  • Compaction
  • Excipient compatibility
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28
Q

Define enthalpy of fusion

A

Change in enthalpy resulting from a change in state

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29
Q

What is melting point defined as?

A

Temperature needed to break bonds

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30
Q

What does differential scanning calorimetry determine?

A

melting point and enthalpy of fusion - a drug is heated, when it undergoes a phase change there is an endothermic reaction.
The point of melting is the peak where there is a change in state

31
Q

Are polymorphs stable?

A

No - they will slowly crystallise to the stable form

32
Q

How do amorphous structures occur?

A

High molecular weight molecules such as polymers or biological structures.
Precipitation can also cause them to occur.

33
Q

Do polymorphs have better solubility?

A

Yes, results in faster dissolution

34
Q

When does polymorphism occur?

A

When a compound exists in at least 2 different molecular arrangements in the solid state

35
Q

What can be said about the most stable polymorph?

A
  • has a high melting point

- exists in a thermodynamic state of eqm (other forms convert to this over time)

36
Q

What will X-ray powder diffraction do for polymorphs?

A

provide solid state structure

37
Q

What will DSC do for polymorphs?

A

Give more than one melting point if there are polymorphs present

38
Q

Is the amorphous form of novobiocin more soluble?

A

Yas

Crystalline one is used for modified release

39
Q

What forms does Ampicillin exist as?

A

Anhydrous and trihydrate

- anhydrous dissolves faster than trihydrate so there is less of an energy change with its dissolution

40
Q

How is Ferets diameter determined?

A

Measuring diameter is different orientations

41
Q

How is Martin’s diameter determined?

A

Measuring the radius from different places in the particle and calculating mean radius

42
Q

Particles with a diameter of …. or less have ….. flow properties

A

Diameter 50mcm

Poor

43
Q

Why is good flow needed?

A

To ensure blend uniformity and optimal filling

44
Q

How can flow be measured?

A

Angle or repose

Carr’s index

45
Q

What angle of repose is unsatisfactory for flow?

A

> 45 degrees

46
Q

What angle of repose is good for flow?

A

close to 25 degrees

47
Q

What does Carr’s index relate to?

A

Flowability and compaction

48
Q

How is Carr’s index calculated?

A

Measuring bulk density and tapped density

49
Q

What is bulk density?

A

Adding mass of powder to cylinder then calculating density (mass / volume)

50
Q

What is the tapped density?

A

When the cylinder is tapped to see if there is any change in volume

51
Q

What is compaction?

A

The result of compression and cohesion

52
Q

What happens when the drug is a low dose?

A

The majority if the tablet is the excipient

53
Q

What happens the dose increases >50mg?

A

Compaction properties of the drug influence the properties of the tablet

54
Q

What does brittleness aid?

A

Aid bond formation

55
Q

Why is the paddle method preferred for determining solubility?

A

Gives reproducible results - only one face of the disc is exposed

56
Q

What does introducing a hydrophilic group do?

A

Improves solubility 100 fold

57
Q

What effect does using a metastable polymorph have on solubility?

A

Increases solubility as the amorphous form is more soluble

58
Q

What is solvation / hydration?

A

Incorporation of solvent molecules into the crystal structure - less energy released for hydrated form to dissolve but in non-aq solvent there is an increase in soluble

59
Q

What is Ka and what effect does it have on solubility?

A

It is the dissociation constant represents concs of ionised an unionised species.
Larger Ka = more dissociation = higher solubility

60
Q

When are drugs converted to salts?

A

If they have poor aqueous solubility or if they are difficult to isolate or purify.

61
Q

When are salts formed?

A

When an acid reacts with a base

62
Q

If pKa is <5 what happens in terms of salt formation?

A

The salt formed is unlikely to be stable at physiological pH - it will precipitate at a concentration above its solubility.

63
Q

What is needed for salt formation to occur?

A

There should a sufficient different in pKa between the acid and base

64
Q

What happens when a basic drugs reacts with a strong acid?

A

The conjugate acid and base form a salt.

When it dissociates in water, it donates its H+ this lowers the pH of the solvent and increases drug solubility

65
Q

What are the advantages of salt formation?

A
  • Enhanced solubility
  • Increased dissolution rate
  • Increased melting point
  • Reduced hygroscopicity
  • Improved photostability
  • Better taste
  • Increased bioavailability
  • Better processabilty
  • Easier synthesis / purification
  • Potential for controlled release
66
Q

What are the disadvantages of salt formation?

A
  • Lower % of API
  • Increased hygroscopicity
  • Reduced chemical stability
  • Increased number polymorphs
  • Reduced dissolution in gastric media
  • No change in solubility buffers
  • Corrosiveness
  • Possible disproportionation
  • Additional manufacturing step
  • Increased toxicity
67
Q

What is contact angle a result of?

A

Interfacious energies of:

  • surface tension of the liquid,
  • tension between solid and vapour
  • tension between solid and liquid
68
Q

What does a contact angle of <90° suggest?

A

Wetting of the surface is favourable

69
Q

What does a contact angle of >90° suggest?

A

Wetting of the surface is unfavourable

70
Q

How can surface tension be reduced?

A

By adding a wetting agent e.g. SLS or polysorbate

71
Q

Describe plastic flow

A

Particles don’t flow until pressure is applied

72
Q

What is pseudoplastic flow?

A

When pressure is applied, flow is increased

73
Q

Describe dilatant flow

A

When particles flow at low pressure but have friction at higher pressures.

Pharm Y2S2 Medicine (10 decks)

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