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PHA111 > Stability of Medicines > Flashcards

Stability of Medicines Flashcards

1
Q

define stability?

A

ability to retain the original characteristics during manufacture, transport, storage and use

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2
Q

what are the 3 main factors in product stability?

A
  • physical stability
  • microbial stability
  • chemical stability
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3
Q

chemical/microbial degradation of surfactant may lead to…

A

emulsion cracking

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4
Q

hydrolysis of antimicrobial agent may lead to…

A

loss of protection against microbial spoilage

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5
Q

adoption into container may lead to…

A

apparent loss of active agent

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6
Q

hygroscopic properties may lead to powders liquefying.

what may this lead to?

A

suppositories losing structure

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7
Q

physical instability

change in bioavailability

A
  • alteration of drug solubility

- loss of active through evaporation

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8
Q

physical instability

change in medicine form

A
  • separation of liquid phases in emulsions

- setting of solids in suspension

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9
Q

physical instability

changes in patient acceptability

A
  • alteration of viscosity
  • change in colour, odour, taste
  • production of particulate matter
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10
Q

what does the polymorph form I have?

A

highest MP, lowest solubility + dissolution rate

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11
Q

if there is crystal growth, what happens to dissolution rate?

A

slows

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12
Q

a use of stable polymorph in chloramphenicol palmitate leads to what?

A

low blood levels

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13
Q

what are particles less than 1m termed?

A

colloids

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14
Q

what are particles more than 1m termed?

A

coarse suspensions

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15
Q

what does stokes law apply to?

A

course suspensions

large particles settle too quick
small settle too slow and cake

partially soluble drug may change size if temp changes

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16
Q

what do small droplets reduce ?

A

partial separation of disperse phase

17
Q

what does high viscosity reduce?

A

creaming

18
Q

incompatibility

pharmacological

A

beta blockers and salbutamol

19
Q

incompatibility

pharmacokinetics

A

tetracyclines + some antacids

20
Q

incompatibility

apparent interactions

A
  • precipitation
  • colour change
  • phase separation
21
Q

incompatibility

physicochemical

A

drug excipient interactions

22
Q

what area of pre-formulation is often overlooked?

A

Maillard reaction between chlorpromazine + dextrose

23
Q

physicochemical effects

A

solvent effect on solubility

e. g. diazepam
- poor water solubility
- mixture -> precipitate depending on conc
- 1:10 / 1:20 insoluble
- 1:50 / above clear for 24 hours

24
Q

if acidic drug is poorly water soluble, what happens?

A

may = given as more water soluble salt (Na / K)

  • if pH dec more drug converted to HA
  • solubility dec
  • pH at which precipitates depends on pKa + INTRINSIC solubility
25
Q

if basic drug is poorly water soluble, what happens?

A

may = given as more water soluble salt (hydochloride, sulphate)

  • pH inc -> more drug converted to B
26
Q

what affects the rate of hydrolysis?

A
  • pH
  • temp
  • moisture
  • solubility
27
Q

if the R group donates electrons into the carbonyl, what happens to the ester?

A

less prone to hydrolysis

C2H4Cl reacts faster than C2H5

28
Q

weaker bases are…

A

better leaving groups

29
Q

phenols are stronger acids than alcohols.

if the R groups = phenyl, what happens?

A

rate inc

30
Q

why is the hydrolysis of amides less reactive?

A

more basic leaving group + less electron withdrawing effect of N in amide compared to O in ester

31
Q

molecular oxygen

A
  • ground state oxygen = di-radical
  • both unpaired electrons in HOMO have same spin
  • singlet oxygen reacts with organic comp (combustion)
  • molecular oxygen will react with radicals
32
Q

oxidation initiation

A
  • oxygen = not good initiator

- use UV

33
Q

state the C-H bonds, starting with the highest stability

A 
benzyl radical 
allyl radical 
tertiary radical 
secondary radical 
primary radical 
vinyl radical 
methyl radical
34
Q

how can u minimise oxidation?

A
  • prevent initiation
  • protect from light
  • limit peroxides
  • use optimum pH (acidic drugs degrade more
    when ionised)
  • add chelating agent to remove metal ions (EDTA + citric acid)
  • stop propagation
  • exclusion of oxygen - pack under inert gas (N) + tablet strips
  • add antioxidant (ascorbic acid)
  • chain terminators (BHT act as radical traps)

PHA111 (30 decks)

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