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Physical pharmacy - DF > Matt Roberts > Flashcards

Matt Roberts Flashcards

1
Q

How do you analyse a drugs solubility?

A

UV spectroscopy - chromophore 190-290nm

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2
Q

What is intrinsic solubility?

A

The solubility of unionised drug

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3
Q

At what temperatures do they test the intrinsic solubility of drugs?

A

4oC - densest point of water

37oC - body temperature

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4
Q

What is the phase solubility of a drug?

A

The ratio of the drug:solvent

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5
Q

What does it mean when the data of a drug deviates in a phase solubility diagram?

A

Sign of impurities

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6
Q

How do you work out intrinsic solubility from a phase solubility diagram?

A

Extrapolate back to zero - only approx

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7
Q

How do you determine the pka of a base?

A

pka = pH + log (Cs - Co / Co)

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8
Q

How do you determine the pka of an acid?

A

pka = pH + log (Co / Cs - Co)

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9
Q

How can you improve the solubility of a drug?

A

Adjusting the pH
Salt formation of the drug
Put drug in non-aq solvent - liquid formulation

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10
Q

What are the disadvantages of strong acids/bases when forming a salt?

A

Form very soluble salts - but hygroscopic - absorb water which leads to instability

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11
Q

What is the diffusive layer of a salt?

A

A saturated solution surrounding the crystal - pH micro-environment

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12
Q

What is the purpose of the diffusive layer?

A

It acts as a buffering agent against the surrounding pH - protects the drug

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13
Q

Do salts change the pharmacological action of a drug?

A

No they only change the physical properties

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14
Q

List three pharmaceutical solvents? And typically what are these co-solvents limits?

A

Glycerol <10%

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14
Q

What is paracetamol’s shelf-life at pH9?

A

4 months

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15
Q

List some dosage form which use oils?

A

Emulsions
Topical formulations
Intra muscular injections
Liquid filled oral preparations - cod liver oil tablets - mask the taste

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15
Q

What liquid is used when determining log P of a drug? Why?

A

Octanol - mimics biological absorption in the GIT

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16
Q

What are solvents called that are less polar than octanol?

A

Hyperdiscriminating - blood brain barrier BBB

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16
Q

What are solvents called that are more polar than octanol?

A

Hypodiscriminating - buccal

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17
Q

What is dissolution rate?

A

The rate at which a solid drug releases into a solution

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17
Q

How can you test the dissolution rate of a drug?

A

Basket method - drug placed in a basket as it floats

Paddle method - drug placed at the bottom of the container as it sinks

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18
Q

What are the units of intrinsic dissolution rate?

A

mg min-1 cm-2

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18
Q

What is the common ion effect? Example.

A

Addition of a common ion reduces solubility - water molecules removed as solvent as competition from other ions for hydration
e.g. H2O vs H20 + 1.2%w/v NaCl

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19
Q

Name three methods to determine melting points of drugs?

A

Capillary method
Hot stage microscopy HSM
Differential scanning calorimetry DSC

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19
Q

What is a polymorph?

A

A solid material with two or more different molecular arrangements (patterns) that give a distinct crystal species

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20
Q

How can polymorphs be identified?

A

X-ray powder diffraction
Solid state nuclear magnetic resonance
IR or Raman spectroscopy

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20
Q

What is the difference between a pseudopolymorph and a polymorph?

A

In pseudopolymorphism the different crystal types are as a result of hydration or solvation

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21
Q

What methods can be used to determine particle size and shape?

A

Nanophox - photon cross-correlation spectroscopy PCCS

Sieving analysis - range and distribution

21
Q

How can you measure powder flow?

A

Angle of repose

Carr’s consolidation index

22
Q

What features improve particle flow?

A

Increased particle size

uniform particle density and shape (spherical)

22
Q

What stability assays are used to assess a drug?

A

UV analysis
Chromatography
Thin layer chromatography TLC
High performance liquid chromatography HPLC

23
Q

Define shelf-life?

A

Period of time that a product retains acceptable chemical, physical and microbiological stability

23
Q

Define expiry date?

A

Given on the product packaging to indicate the end of the shelf-life

24
Q

Define instability?

A

A change in the physicochemical properties of a pharmaceutical product

24
Q

What happens to the drug when it is unstable?

A

Reduced efficacy - API less effective

Increased toxicity - API reacts to form a product which has undesirable effects

25
Q

How long will a stable drug last?

A

2-5 years

25
Q

How long will an extremely stable drug last?

A

More than 5 years

26
Q

How long will a moderately stable drug last?

A

Roughly 2 years

27
Q

How long will an unstable drug last?

A

Less than 1 year

28
Q

What are the two most common interactions which cause instability?

A

Drug - excipient interaction

Packaging interaction

29
Q

Give two examples of drug - excipient interaction?

A

Mg2+ ions and Fosinopril

Lactose and Fluoxetine

30
Q

How can temperature affect drug stability?

A

Greater free energy so more rapid reactions - becomes unstable quicker than normal

31
Q

How can light affect drug stability?

A

Photolysis which puts in initial energy for degradation

e.g. photolytic oxidation

32
Q

How can water affect drug stability?

A

Can cause the drug to hydrolyse

33
Q

How can you prevent hydrolysis of a drug? (5)

A

Exclude water from the formulation
Remove metal ions - catalyse reactions like hydrolysis
Add a chelating agent - traps metal ion so unable to catalyse the hydrolysis of the drug
Buffer at pHmin - pH at which the drug is most stable
Store at low temperature - increases hydrolysis rate
Protect from light - UV radiation enough to initiate photolytic reactions

34
Q

How can oxidation affect drug stability?

A

Change bonding within molecule
Possible increase in MW
Change in colour

35
Q

How can you prevent oxidation? (4)

A

Remove oxygen from the formulation
Protect from light - photolytic oxidation is common
Remove metal ions - oxidation catalysed by metal ions
Add antioxidants - oxidised easier than drug so drug unaffected

36
Q

Name the three types of antioxidants?

A

Sulphur containing antioxidants - sodium bisulphite
Free radical scavengers - ascorbic acid
Fat soluble antioxidants - butylated hydroxytoluene

37
Q

How long will an extremely stable drug last?

A

More than 5 years

38
Q

How long will a moderately stable drug last?

A

Roughly 2 years

39
Q

How long will an unstable drug last?

A

Less than 1 year

40
Q

What are the two most common interactions which cause instability?

A

Drug - excipient interaction

Packaging interaction

41
Q

Give two examples of drug - excipient interaction?

A

Mg2+ ions and Fosinopril

Lactose and Fluoxetine

42
Q

How can temperature affect drug stability?

A

Greater free energy so more rapid reactions - becomes unstable quicker than normal

43
Q

How can light affect drug stability?

A

Photolysis which puts in initial energy for degradation

e.g. photolytic oxidation

44
Q

How can water affect drug stability?

A

Can cause the drug to hydrolyse

45
Q

How can you prevent hydrolysis of a drug?

A

Exclude water from the formulation
Remove metal ions - catalyse reactions like hydrolysis
Add a chelating agent - traps metal ion so unable to catalyse the hydrolysis of the drug
Buffer at pHmin - pH at which the drug is most stable
Store at low temperature - increases hydrolysis rate
Protect from light - UV radiation enough to initiate photolytic reactions

46
Q

How can oxidation affect drug stability?

A

Change bonding within molecule
Possible increase in MW
Change in colour

47
Q

How can you prevent oxidation? (4)

A

Remove oxygen from the formulation
Protect from light - photolytic oxidation is common
Remove metal ions - oxidation catalysed by metal ions
Add antioxidants - oxidised easier than drug so drug unaffected

48
Q

Name the three types of antioxidants?

A

Sulphur containing antioxidants - sodium bisulphite
Free radical scavengers - ascorbic acid
Fat soluble antioxidants - butylated hydroxytoluene

49
Q

What is refrigerator temp?

A

2-8oC

50
Q

What is freezer temp?

A

-20oC

51
Q

What temp should a drug be kept at when it says keep ‘cool’?

A

8-15oC

52
Q

What is room temp?

A

15-30oC

53
Q

Name three drug substance stability tests?

A

Stress testing - identify likely degradation products
Accelerated testing - early estimate on retest date
Long term testing - establishes retest period and storage conditions

54
Q

Name two drug product stability tests?

A

Accelerated tests - early indication of shelf-life

Long term tests - establish shelf-life and storage conditions

55
Q

Define retest date?

A

The date on which the material should be examined to ensure it still complies with its quality specification

56
Q

Define expiry date?

A

The last date on which the product can be expected to comply with its quality specifications (if stored correctly)

Physical pharmacy - DF (9 decks)

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