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PMP 102 Drugs & Medicines > Stability of Medicines > Flashcards

Stability of Medicines Flashcards

1
Q

Stability

A

Capacity of a product to remain within specifications to ensure potency, quality or purity

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2
Q

Chemical degradation

A
  • Decomposition of chemical moiety
  • Due to effects of moisture, oxygen, light & heat
  • Results in loss of active drug
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3
Q

Physical degradation

A
  • Formulation-specific
  • Caking in suspensions, phase separation in emulsions
  • Hardness & brittleness of tablets
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4
Q

Microbial degradeation

A
  • Microbial contamination
  • Metabolism of drug molecule
  • Physical spoilage of dosage form
  • Infection-causing
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5
Q

Drug instability may cause

A
  • Inconsistent dosage
  • Undesired change in performance dissolution/bioavailability
  • Changes in physical appearance of the dosage form
  • Product failures
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6
Q

Chemical degradation reactions

A
  • Hydrolysis
  • Oxidation
  • Photodegradation
  • Polymerisation and dimerisation
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7
Q

Hydrolysis

A
  • Most common chemical degradation
  • Water present in many pharmaceuticals as ingredient or contaminant
  • Carboxylic acid derivatives are common in medicines
    Esters and amides
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8
Q

Imide

A
  • N-H
  • 2 Carbonyal
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9
Q

Urea

A
  • 2x NH2
  • Carbonyal group
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10
Q

Rate of hydrolysis is reduced by

A
  • Dry formulations (powder for reconstitution, solid dosage form)
  • Adjusting pH to maximum stability in aqueous solution
  • Storage temperature
  • Coating
  • Choice of packaging
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11
Q

Hydrolysis reduction

Complexation

A
  • Caffeine (a xanthine) complexes with local anesthetics, such as benzocaine and procaine
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12
Q

Hydrolysis reduction

Surfacant

A
  • Drug molecules become trapped in the micelle
    Hydrolytic groups such as OH cannot penetrate the micelle and reach the drug molecules
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13
Q

Oxidation

A
  • Removal of H, loss of e-, addition of O
  • Generally occurs via the action of free radicals
  • Highly reactive species possessing one or more unpaired electrons
  • Generated by the action of light energy (UV), heat or trace metals such as Fe2+ or Cu+
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14
Q

Auto-oxidation

A
  • Uncatalysed and proceeds slowly under the influence of molecular oxygen
  • Reaction of free radicals with drugs or biomolecules leads to the formation of peroxyl radicals, which initiate and propagate auto-oxidation
  • Initiation, Propogation and Termination
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15
Q

Prevent auto-oxidation

Remove initiators

A

Chelation of trace metals with chelating agents: ethylene diamine tetraacetic acid (EDTA), citric acid & tartaric acid

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16
Q

Prevent auto-oxidation

Exclude oxygen

A

Sparge liquids with inert gases such as nitrogen to displace oxygen

17
Q

Prevent auto-oxidation

Add free radicals

A
  • More readily oxidised at lower redox potention
18
Q

Photochemical degradation

A
  • Energy of a photon increases with decreasing wavelength inverse proportional
  • UV light has high energy which can catalyse reactions
  • UV light could cause oxidation, polymerisation
  • Ring rearrangement
19
Q

Polymerisation

A
  • A process by which two or more identical drug molecules combine together to from a complex molecule
  • UV radiation induces the polymerisation of chlorpromazine
20
Q

Photolysis

A
  • Decomposition by light
  • last for a year without light
  • 4 hours with light
21
Q

Prevent photolysis

A
  • Exclude from light
  • Packaging in foil
  • Filter out light by
  • Storage in amber glass or Coating tablets with pigmented polymers
22
Q

Zero order reaction

A
  • Degradeation of drug increases as time increases regardless of concention of drug
23
Q

First order

A
  • Degradeation directally proportional to it concentration
  • ln() funtion then it is first order
24
Q

Pseudoreaction

A
  • lots of solid dissolving degrade dependant on concentration but regardless of concentration
  • Initially zero order to first
25
Q

Second order

A
  • The rate of degradation of A is directly proportional to its concentration and the concentration of the reactant B
  • Length of half life increases with decreasing concentration
26
Q

Acceptable degradeation

Toxicity of degradation products

A

Antifungal drug flucytosine degrades to fluorouracil (cyctotoxic)

27
Q

Acceptable degradation

Physical properties of dosage form

A

Irreproducible dose

28
Q

Acceptable degradation

Aesthetics (look & feel)

A

Adrenaline degrades to red adrenochrome (unsightly)

29
Q

Acceptable degradedation

A

5-10% loss of overall limit

30
Q

Expiry date

A
  • Accelerated testing in extream conditions
  • measure degradation
31
Q

Arrhenius equation

A

Ae^-Ea/RT

32
Q

Components of Arrenius equation

A
  • ln(a) is y-intercept
  • Gradient -Ea/R
  • X intercept 1/T
33
Q

Why Arrhenius?

A

Duning accelerated testing at high temperature measure degradeation

PMP 102 Drugs & Medicines (56 decks)

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