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Pharmaceutics > Preformulation > Flashcards

Preformulation Flashcards

1
Q

What is the most popular dosage form?

A

Tablets

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2
Q

Why is preformulation needed?

A

To give info on:
Feasibility of dosage forms
Potential drug instability
Poor in vivo dissolution

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3
Q

What are excipients?

A

Inactive substances that are used as vehicles or medium for drugs or other active substances

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4
Q

What is a problem with preformulation?

A

Only limited quantities of compound will be available

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5
Q

Why is it important not to skip preformulation?

A

Cost of reformulation can be high
Formulation can go wrong ect. When solubility of low, formulation of injections is not possible
Concept of minimum preformulation

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6
Q

What is minimum preformulation?

A

Getting as much information as possible form the small amount of material available

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7
Q

What two properties should be measured first?

A 
Intrinsic solubility (C0)
Dissociation constant (pKa)
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8
Q

What amount of drug should be used for measuring solubility?

A

50 mg

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9
Q

Why are new compounds of poor quality?

A

Lots of unknown impurities

Different crystal forms

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10
Q

What does the solubility dictate?

A

The ease of obtaining formulations of aqueous solutions

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11
Q

What does measuring the pKa allow?

A

Information given of pH to maintain solubility

Allows informed choice of salts which gives good bioavailability

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12
Q

What does solubility affect?

A

Drug absorption

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13
Q

What pH range should drugs solubility be?

A

Solubility of more than 1% at pH range 1-7

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14
Q

What temperature should drugs solubility be?

A

37oC

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15
Q

What is absorption rate limited by?

A

Dissolution rate

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16
Q

What is solution?

A

A mixture of two or more components that form a single phase homogeneous down to molecular level

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17
Q

What is solvent?

A

A component that determines the phase

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18
Q

What is solute?

A

The component which is dispersed

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19
Q

What is dissolution?

A

Transfer of molecules or ions from solid state into the solvent

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20
Q

What is a saturated solution?

A

A solution in which the solvent has dissolved all of the solute that it can

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21
Q

What is solubility?

A

The maximum concentration that can be attained by a solute in a specific solvent

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22
Q

What is the quantity per quantity expression of solubility?

A

1gL-1 or 0.1g per 100 mL

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23
Q

What is molality expressed in?

A

Moles per 1000g

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24
Q

What is molarity expressed in?

A

Moles per litre

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25
Q

What is mole fraction expressed in?

A

Moles per total number of moles

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26
Q

What is parts expressed in?

A

Number of weight parts solid/number of volume parts of solvent

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27
Q

What is the solubility if a very soluble compound?

A

Less than 1

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28
Q

What is the solubility of a practically insoluble or insoluble drug?

A

More than 10,000

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29
Q

What does an increase in solubility suggest the compound is?

A

A weak base

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30
Q

What does increased solubility in alkaline aqueous solutions suggest the compound is?

A

A weak acid

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31
Q

What does an increase in solubility under both acidic and alkaline conditions suggest?

A

That the compound is amphoteric or zwitterionic so two pKa values

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32
Q

What does no change in solubility over a range of pH suggest?

A

That the compound is neutral and non-ionisable (no pKa)

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33
Q

How can solubility be improved?

A 
pH (use of buffers)
Salts
Use of co-solvents
Use of surfactants
Complexation
Solid dispersion
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34
Q

What pH range buffers used?

A

pH 3-9

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35
Q

Why are extreme pH values used for buffers?

A

Injections would cause tissue damage and pain

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36
Q

What pH is acidic drugs formulated in?

A

Basic pH

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37
Q

What pH is basic drugs formulated in?

A

Acidic pH

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38
Q

What can salts do in regards to solubility?

A

Improve solubility

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39
Q

How are salts formed?

A

By acid base reactions

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40
Q

What should the pKa for each component not be?

A

Too close together (

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41
Q

Why is it better to use walk acid or base?

A

These says tend to be less soluble but also less hygroscopic

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42
Q

Give an example of salts of acidic drugs?

A

Sodium salicylate

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43
Q

Give example of salts of basic drugs?

A

Meperidine hydrochloride

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44
Q

What are acidic groups in drugs?

A

COOH

OH and SH (thiol) if attached to an electron-withdrawing group

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45
Q

What is a basic group in drugs?

A

Amino groups

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46
Q

What is co-solvency?

A

The mixing solvents of different polarities to form a solvent system of optimum polarity to dissolve the solute

47
Q

Why are co-solvents added to water?

A

To increase the solubility
To increase stability
Injection formulation

48
Q

What is the dielectric constant of the solvent used for?

A

When developing the co-solvent system

49
Q

What could injections contain?

A
50
Q

What should solubility be measured in?

A

Aqueous/co-solvent mixtures (formulations rarely require pure co-solvent)

51
Q

What do surfactants have?

A

A polar head and a lipophilic tail group

52
Q

What can surfactants form?

A

Micelles at concentrations higher than the critical micelle concentration. Hydrophobic drugs can diffuse inside the micelle

53
Q

What must surfactants be?

A

Non-toxic
Miscible with the solvent
Compatible with other ingredients
Odourless

54
Q

Give an example of non-ionic surfactants

A

Glycol/glycerol

55
Q

Give an example of alkali metal and ammonium soaps

A

E.g. Sodium stearate

56
Q

What are commonly used as complexing agents?

A

Cyclodextrins

57
Q

What are Cyclodextrins?

A

6-8 glucopyranose units forming cyclical structures like hollow cylinders/baskets . Inside is hydrophobic and rim is hydrophilic

58
Q

The more hydrophobic a drug what happens to the effect of the co-solvent?

A

Increases

59
Q

What is lipophilicity measured using?

A

Oil-water partition coefficient (log P)

60
Q

What does it mean when P=1?

A

The drug has equal affinity for both oil and water

61
Q

What does it mean if P>1?

A

The drug is lipophilic (hydrophobic)

62
Q

What does it mean if P

A

The drug is hydrophilic

63
Q

Why is the logarithm scale used?

A

As the values of P may be very large

64
Q

Name the variety of methods used for determining melting point

A

Capillary melting-observation of melting in a capillary tube in a heated metal block
Hot stage microscopy- observation of melting under a microscope (more precise)
Differential scanning calorimetry or differential thermal analysis

65
Q

What is the pro/con of capillary melting?

A

Gives information on melting range but accuracy is low

66
Q

What are the advantages of hot stage microscopy?

A

Heating rate of controlled

Other transitions can be observed/recorded

67
Q

What does differential scanning calorimetry measure?

A

The amount of energy required to keep the sample at the same temperature as the reference. The enthalpy of the transition is measured

68
Q

What is differential thermal analysis?

A

DTA measures the temperature difference between the sample and a reference as function of temperature or time while the sample and the reference are subjected to a controlled temperature program

69
Q

What changes of state are DSC and DTA useful for quantifying?

A 
Crystalline transitions
Fusion
Evaporation 
Sublimation
Crystal purity
Polymorphism
70
Q

What is s polymorph?

A

A solid material with at least two different molecular arrangements. Distinct crystal species

71
Q

What can polymorphism affect?

A

Stability, dissolution rates and solubility

72
Q

What are highest melting polymorph have in regards to stability and solubility?

A

Most stable

Least soluble

73
Q

What are polymorphs numbered in?

A

Order of stability at room temperature

E.g. Form I > Form II> Form III ect.

74
Q

What do crystals with weak bonds have?

A

Low melting point and low heat of fusion

75
Q

What are the majority of drugs and excipients?

A

Crystalline solids

76
Q

What are the two consecutive stages of dissolution?

A

An interfacial reaction which is liberation of solute molecules
A migration step

77
Q

What does dissolution involve?

A

The replacement of crystal molecules by solvent molecules

78
Q

What must solvent/solute attraction forces overcome?

A

Cohesive forces of attraction between molecules of the solid

79
Q

What are liquids thought to contain?

A

Free volume in the form of holes not occupied by solvent molecules

80
Q

What occupied theses holes in liquids?

A

Solute molecules

81
Q

What does the migration step involve?

A

Transport of drug molecules away from solid/liquid interface and into the bulk liquid

82
Q

What does the migration step occur through?

A

Diffusion or convection

83
Q

What are boundary layers?

A

Static/ slow-moving liquid layers that surround all solid surfaces surrounded by liquids

84
Q

What does slow mass transfer result in?

A

Inhibition of movement of drug from solid surface and into bulk liquid

85
Q

During diffusion, what does the concentration of solution in boundary layers go from?

A

Saturated at the crystal surface to being equal to the concentration in the bulk

86
Q

What is intrinsic solubility (C0)?

A

The solubility of the drug compound when it is completely unionised

87
Q

For the intrinsic solubility what do you measure the solubility of a weak acid in?

A

In a acidic solution

88
Q

For the intrinsic solubility what do you measure the solubility of a weak base in ?

A

Alkaline solution

89
Q

What two temperatures should the solubility of a drug be measured at?

A

4oC- water solubility is minimum

37oC- the solubility at body temperature

90
Q

What can impurities do in regards to solubility of a drug compound?

A

Increase, decrease or have no effect

91
Q

What can reasonable estimation of C0 be made by using?

A

A phase solubility diagram

92
Q

What are phase solubility diagrams?

A

These are obtained by varying the drug : solvent ratio, measuring the solubility and plotting the resulting data

93
Q

What does it mean if phase solubility diagram has deviation from horizontal?

A

Sample contains no impurities

94
Q

What does it mean if the line in extrapolated to zero phase ratio on a phase solubility diagram?

A

C0

95
Q

Name a super-solvent?

A

Dimethylsulfoxide DMSO

96
Q

How can solubility be measured?

A

SiriusT3 and 96-well micro-titre plate

97
Q

What % of drugs are weak bases?

A

75%

98
Q

What % of drugs are weak acids?

A

20%

99
Q

What % of drugs are non-ionic,amphoteric of alcohols?

A

5%

100
Q

What is the degree of ionisation in a drug measured by?

A

pKa

101
Q

What does an increase in solubility in acidic aqueous solution suggest?

A

That the compound is a weak base

102
Q

What does an increase in solubility on alkaline aqueous solution suggest?

A

That the compound is a weak acid

103
Q

What does an increase in solubility in both acidic and alkaline conditions suggest?

A

That the compound is either amphoteric or zwitterionic

104
Q

What does no change in solubility over a range of pH suggest?

A

That compound is neutral and non-ionisable (no pKa)

105
Q

What can Henderson-Hasselbach equation be used to?

A

Determine pKa by following changes in solubility

Predict solubility at any pH (knowing C0 and pKa)

106
Q

What is Cs?

A

The total solubility so the ionised and unionised form

107
Q

What is the solubility in for acid to = Cs?

A

In 0.1M HCL

108
Q

What is the solubility at for acids to = Cs?

A

pH 6 and 8

109
Q

What is the solubility in for a base to = C0?

A

0.1M NaOH

110
Q

What is the solubility at for base = Cs?

A

pH 4 and 6

111
Q

What does an increase in pH of a base mean in regards to solubility?

A

Decrease

112
Q

What does increase in pH of acid mean in regards to solubility?

A

Increase

113
Q

What does at increase in pH of an amphoteric mean in regards to pH?

A

Decrease up to pH 7 then increase

114
Q

What is preformulation?

A

It is the determination of certain fundamental physical and chemical properties of a potential new drug.

Pharmaceutics (6 decks)

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