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PHA111 > Stability of Medicines > Flashcards

Stability of Medicines Flashcards

1
Q

What is stability?

A

Ability to retain the original characteristics during manufacture, transport, storage & use

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2
Q

Name the three main factors in product stability

A
  • Physical stability
  • Microbial stability
  • Chemical stability
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3
Q

What might chemical or microbial degradation of a surfactant lead to?

A

Emulsion cracking

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4
Q

Hydrolysis of antimicrobial agent may lead to what?

A

Loss of protection against microbial spoilage

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5
Q

Adsorption into container may lead to what?

A

Apparent loss of active agent

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6
Q

What are physical instabiliteis?

A
  • Change in bioavailability
  • Change in medicine form
  • Changes in patient acceptability
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7
Q

What is polymorphism?

A
  • Different crystal structures
  • One stable form (I), one or more metastable forms(II)
  • I has highest MP, lowest sol & diss rate
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8
Q

What do polymorphic forms affect?

A

Bioavailability

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9
Q

What does conversion occur more rapidly in?

A

Suspension

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10
Q

Particles below 1um and above 1um are what?

A 
<1um = colloids
>1um = coarse suspensions
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11
Q

What is instability due to?

A

Settling

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12
Q

Partially soluble drug may change ______ if _____ fluctuates

A

particle size

temperature

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13
Q

What are emulsions?

A

Dispersion of two immiscible liquids, one evenly distributed as fine droplets in the other (oil in water or water in oil)

  • Thermodynamically unstable
  • Requires an emulsifying agent
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14
Q

What does partial separation of disperse phase lead to?

A

Creaming in o/w emulsions

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15
Q

What does complete separation of phases lead to?

A
  • Cracking
  • Irreversible
  • Breakdown of emulsifying system
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16
Q

Small droplets reduce ______

High viscosity reduces ______

A

effect

creaming

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17
Q

What is pharmacological incompatibility?

A

opposite effect ‘cancel out’

e.g. b-blockers & salbutamol

18
Q

What is pharmacokinetic incompatibility?

A

Reduces absorption

e.g. tetracyclines & some antacids

19
Q

What is a drug-excipient interaction?

A
  • Reaction between amino acids & sugars

e. g. maillard reaction between chlorpromazine and dextrose

20
Q

List a physiochemical effect

A

solvent effect on solubility

e.g. diazepam, poor water solubility

21
Q

List the pH effects on solubility

A 
- Acidic drug: 
Poorly water soluble
pH decreases more drug converted to HA
Solubility decreases 
pH depends on pKa & intrinsic solubility
  • Basic drug
    pH increases more drug converted to B
22
Q

Effect depends upon _____ concentration and _______ solubility

A

final

intrinsic

23
Q

Supersaturated solutions may not precipitate out immediately, _____ develops in ___ hours

A

Haze

3

24
Q

What to be aware for in hydrolysis for a given drug?

A
  • Recognition of functional groups in drug

- Comparison of reactivity

25
Q

What affects the rate of hydrolysis?

A
  • pH: specified acid or base catalysed
  • temperature: all reactions affected
  • moisture content: humidity, solvent used (reducing water doesn’t always reduce hydrolysis)
  • solubility: dissolved drug reacts much more quickly than solid
26
Q

If R1 groups donate electrons into the carbonyl the ester is less/more prone to hydrolysis

A

less

27
Q

The _____ of the leaving group affects the rate

A

stability

28
Q

Are weaker bases/acids better leaving groups

A

weaker bases

if R2 contains an electron withdrawing group it weakens the base and increases the reaction rate

29
Q

Amide hydrolysis mechanism similar to _____

____ has major influence

A

esters

pH

30
Q

Amides are ____ reactive due to more ____ leaving group and less _____ withdrawing effect of ___ in amide compared to ___ in ester

A 
less
basic 
electron
N
O
31
Q

In thioesters, which bond is stronger?

S-C or O-C

A

O-C

32
Q

Better electronic overlap results between atoms of ______

A

similar size

33
Q

Thioester carbonyl not stabilised by as much ______ as ester carbonyl

A

resonance

34
Q

Thioester _______ reactive than ester

A

more

35
Q

What is autooxidation?

A

Spontaneous oxidation in air at ambient temperatures

36
Q

What is ground state oxygen?

A

A di-radical

37
Q

Both unpaired electrons in HOMO have same ____

Only singlet oxygen have _____

A

spin

opposite spin

38
Q

Molecular oxygen will react with ___________ (____)

A

unpaired electrons (radicals)

39
Q

Is oxygen a good/bad initiator

A

bad

40
Q

Initiation must be able to lose __ or similar to give a relatively _____ _____

A

H

stable radical

41
Q

List ways to minimise oxidation

A
  • Prevent initiation
  • Protect from light
  • Limit peroxides
  • Use optimum pH
    (acidic drugs degrade more rapidly when ionised, basic drugs more stable in acidic conditions)
  • Add chelating agent to remove metal ions
  • Stop propagation
  • Exclusion of oxygen (pack under inert gas)
  • Add antioxidant
42
Q

Give an example of oxidation

A

ACE inhibitor captopril for children with hypertension

  • solid dosage form
  • extemp aq prep which suffer short shelf lives
  • It undergoes oxidative dimerisation

PHA111 (23 decks)

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