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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
What is a polymorph?
A solid material with two or more different molecular arrangements (patterns) that give a distinct crystal species
20
How can polymorphs be identified?
X-ray powder diffraction Solid state nuclear magnetic resonance IR or Raman spectroscopy
20
What is the difference between a pseudopolymorph and a polymorph?
In pseudopolymorphism the different crystal types are as a result of hydration or solvation
21
What methods can be used to determine particle size and shape?
Nanophox - photon cross-correlation spectroscopy PCCS | Sieving analysis - range and distribution
21
How can you measure powder flow?
Angle of repose | Carr's consolidation index
22
What features improve particle flow?
Increased particle size | uniform particle density and shape (spherical)
22
What stability assays are used to assess a drug?
UV analysis Chromatography Thin layer chromatography TLC High performance liquid chromatography HPLC
23
Define shelf-life?
Period of time that a product retains acceptable chemical, physical and microbiological stability
23
Define expiry date?
Given on the product packaging to indicate the end of the shelf-life
24
Define instability?
A change in the physicochemical properties of a pharmaceutical product
24
What happens to the drug when it is unstable?
Reduced efficacy - API less effective | Increased toxicity - API reacts to form a product which has undesirable effects
25
How long will a stable drug last?
2-5 years
25
How long will an extremely stable drug last?
More than 5 years
26
How long will a moderately stable drug last?
Roughly 2 years
27
How long will an unstable drug last?
Less than 1 year
28
What are the two most common interactions which cause instability?
Drug - excipient interaction | Packaging interaction
29
Give two examples of drug - excipient interaction?
Mg2+ ions and Fosinopril | Lactose and Fluoxetine
30
How can temperature affect drug stability?
Greater free energy so more rapid reactions - becomes unstable quicker than normal
31
How can light affect drug stability?
Photolysis which puts in initial energy for degradation | e.g. photolytic oxidation
32
How can water affect drug stability?
Can cause the drug to hydrolyse
33
How can you prevent hydrolysis of a drug? (5)
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
How can oxidation affect drug stability?
Change bonding within molecule Possible increase in MW Change in colour
35
How can you prevent oxidation? (4)
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
Name the three types of antioxidants?
Sulphur containing antioxidants - sodium bisulphite Free radical scavengers - ascorbic acid Fat soluble antioxidants - butylated hydroxytoluene
37
How long will an extremely stable drug last?
More than 5 years
38
How long will a moderately stable drug last?
Roughly 2 years
39
How long will an unstable drug last?
Less than 1 year
40
What are the two most common interactions which cause instability?
Drug - excipient interaction | Packaging interaction
41
Give two examples of drug - excipient interaction?
Mg2+ ions and Fosinopril | Lactose and Fluoxetine
42
How can temperature affect drug stability?
Greater free energy so more rapid reactions - becomes unstable quicker than normal
43
How can light affect drug stability?
Photolysis which puts in initial energy for degradation | e.g. photolytic oxidation
44
How can water affect drug stability?
Can cause the drug to hydrolyse
45
How can you prevent hydrolysis of a drug?
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
How can oxidation affect drug stability?
Change bonding within molecule Possible increase in MW Change in colour
47
How can you prevent oxidation? (4)
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
Name the three types of antioxidants?
Sulphur containing antioxidants - sodium bisulphite Free radical scavengers - ascorbic acid Fat soluble antioxidants - butylated hydroxytoluene
49
What is refrigerator temp?
2-8oC
50
What is freezer temp?
-20oC
51
What temp should a drug be kept at when it says keep 'cool'?
8-15oC
52
What is room temp?
15-30oC
53
Name three drug substance stability tests?
Stress testing - identify likely degradation products Accelerated testing - early estimate on retest date Long term testing - establishes retest period and storage conditions
54
Name two drug product stability tests?
Accelerated tests - early indication of shelf-life | Long term tests - establish shelf-life and storage conditions
55
Define retest date?
The date on which the material should be examined to ensure it still complies with its quality specification
56
Define expiry date?
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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