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PMP102 > Stability of Medicines > Flashcards

Stability of Medicines Flashcards

1
Q

What is a lyophobic system?

A

-Systems that have a poor interaction with the solvent

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2
Q

What law governs sedimentation?

A

-Stokes law

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3
Q

What is homogenous stability?

A

-Even disposal of molecules

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4
Q

What is non-homogenous stability?

A

-Molecules are not dispersed evenly throughout the system

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5
Q

How can sedimentation be prevented?

A

-By adding a co-suspension (specifically formulated phospholipid particles)

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6
Q

What is aggregation?

A

-Particles come together in groups

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7
Q

What is coagulation?

A

-particles that are closely aggregated and difficult to re-disperse

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8
Q

What is sedimentation?

A

-Process of settling or being deposited as a sediment

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9
Q

What is caking ?

A

-Deflocculated particles form cakes which are difficult to re-disperse

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10
Q

What is Ostwald ripening?

A

-Dissolution of small particles and re-disposition of dissolved species on the surfaces of larger crystals

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11
Q

What factors can effect stability?

A

-kinetic properties
-size/shape
-electrical properties

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12
Q

What is Brownain motion?

A

-Random movement of particles

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13
Q

What does fick’s first law determine?

A

-Diffusion rate

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14
Q

What does stokes-einstein equation determine?

A

-Diffusion coefficient

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15
Q

What is the rate of sedimentation dependent on?

A

-The combined forces of gravity and drag

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16
Q

What is viscosity ?

A

-Resistance to flow under an applied stress

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17
Q

What happens to sedimentation rate when viscosity is increased?

A

-Decrease

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18
Q

What is viscosity related to?

A

-Molecular weight of suspended particles and suspending agents

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19
Q

What factors influence the rheology of suspensions?

A

-High volume fractions
-Particle size
-Particle distribution
-Particle shape
-Electrostatic interactions
-Steric hindrance

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20
Q

How can sedimentation be prevented?

A

-Form smaller particles
-Decreases the density difference between the two phases
-Increase viscosity of the continuous phase

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21
Q

How do most surfaces acquire charge?

A

-ion dissolution
-ionisation

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22
Q

What is Zeta potential ?

A

-Magnitude and type (+/-) of the electrical potential at the slipping plane

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23
Q

What does a low (0 to 5 mV) zeta potential mean?

A

-Prone to aggregate

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24
Q

What does a high (>30mV) zeta potential mean?

A

-Tend to remain dispersed

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25
Q

What factors affect zeta potential?

A

-Ion concentration
-pH of continuous phase

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26
Q

How does ion concentration effect zeta potential ?

A

-Charge of ions determines magnitude

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27
Q

How does pH of continuous phase effect zeta potential ?

A

-Alters the ionisation of ionic species in the continuous phase and the surface charge of ionisable groups

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28
Q

What is the DVLO theory?

A

-a quantitive approach to the stability of lyophobic systems that assumes the only interactions involved for Van Der Waals and electrostatic repulsive forces

29
Q

If there is a low energy of repulsion what happens to the particles?

A

-Possible flocculation

30
Q

If there is a high energy of repulsion what happens to the particles?

A

-Will likely remain dispersed

31
Q

What does Va stand for?

A

-Van der Waals forces of attraction

32
Q

What does vR stand for?

A

-Electrical repulsion

33
Q

What happens when Va is high?

A

-Strong attraction - coagulation

34
Q

What happens when Va is closer to the origin?

A

-Weak attraction will mean flaws are formed

35
Q

What happens when Vr is closer to the origin?

A

-Weak repulsion will mean flags are formed

36
Q

How does an emulsion instability occur?

A

-Phase intervention
-creaming
-flocculation
-coalescence
-Ostwold ripening

37
Q

What do droplets do in a stable emulsion?

A

-Retain their initial character and remain uniformly distributed throughout the continuous phase

38
Q

What is phase inversion?

A

-Oil-in-water is stabilised by co-surfactant charge on emulsion is reduced through addition of ions via buffer or drug so droplets will come together
-Once in contact, interfacial surfactant film re-aligns forming water-in-oil

39
Q

What is creaming?

A

-Due to the density difference between oil and water, oil droplets tend to concentrate at the top of the emulsion

40
Q

How can creaming be avoided?

A

-Increases the oil density or viscosity of the emulsion

41
Q

What is flocculation in an emulsion?

A

-When two or more emulsion droplets aggregate without losing their individual identity

42
Q

What is coalesnce?

A

-Occurs when two or more droplets collide and form one larger droplet and is irreversible

43
Q

What causes coalescence?

A

-Surfactant type
-Concentration of surfactant
-pH
-Temperature

44
Q

What factors cause van der Waals forces to vary?

A

-Distance between pairs of atoms or molecules

45
Q

What type of surfactants does DVLO theory apply to?

A

-Ionic

46
Q

Why doesn’t DVLO theory apply to non-ionic surfactants ?

A

-No electrostatic charge is present so the charge on the droplet is neutral

47
Q

What are steric effects?

A

-When two particles comes into contact a polymer chain starts to overlap leading to a loss in freedom/entropy. This is thermodynamically unfavourable and forces the droplets apart

48
Q

What are salvation forces?

A

-The two particles come into contact and polymer chains overlap forming a concentrated polymer solution inducing an osmotic gradient in the solution. Water enters the concentrated region in an attempt to dilute it and on doing so forces the polymer chains and droplets apart

49
Q

What are the 4 types of forces in emulsions?

A

-Van Der Waals (+)
-Electrostatic (-)
-Steric (-)
-Solvation (-)

50
Q

What forces are most important in charged colloids?

A

-Van der Waals
-Electrostatic

51
Q

What forces are most important in uncharged colloids?

A

-Van der Waals
-steric
-Solvation

52
Q

What emulsions achieve best stability?

A

-Emulsions where electrostatic, steric and salvation forces can be present

53
Q

What is stability?

A

-The capacity of a product to remain within specifications to ensure potency, quality or purity

54
Q

What can instability cause?

A

-Inconsistent dose
-Undesired change in performance
-Changes in physical appearance of the dosage form
-Product failures

55
Q

What is chemical degradation?

A

-Decomposition of chemical moiety due to effects of moisture, oxygen, light and heat which can result in the loss of active drug

56
Q

What is the physical degradation?

A

-Formulation-specific : caking in suspensions, phase separation in emulsions which can cause hardness and brittleness of tablets

57
Q

What is microbial degradation?

A

-Microbial contamination: metabolism of drug molecule or physical spoilage of dosage form that can lead to infection

58
Q

What chemical degradation reactions occur?

A

-Hydrolysis
-Oxidation
-Photodegradation
-Polymerisation and dimerisation

59
Q

Why is hydrolysis the most common chemical degradation?

A

-Water is present in many pharmaceuticals and carboxylic acid derivatives (esters and amines) are also common

60
Q

How is hydrolysis reduced to prevent chemical degradation?

A

-Dry formulations
-Adjusting pH to maximise stability in aqueous forms
-Storage temperature
-coating
-Choice of packaging

61
Q

How is the rate of hydrolysis reduced to prevent chemical degradation?

A

-Complexation
-Surfactants

62
Q

How does oxidation break down drugs?

A

-Removes H+, loss of e- and addition of O usually through free radicals

63
Q

What are free radicals?

A

-Highly reactive chemicals unpaired electrons

64
Q

What is auto-oxidation ?

A

-The formation of peroxyl radicals which initiates and propagates auto-oxidation in the propagation step

65
Q

What are the ways you can overcome auto-oxidation?

A

-Remove initiators
-Excludes O2
-Add free-radicals scavengers

66
Q

How does removing initiators reduce auto-oxidation?

A

-Chelation of trace metals with chelating agents; EDTA, citric acid and tartaric acid

67
Q

How can you exclude O2 to prevent auto-oxidation?

A

-Sparge liquids with inert gases eg nitrogen to displace oxygen

68
Q

How does adding free radicals prevent auto-oxidation?

A

-Butylted hydroxytoluene is more readily oxidised than oils

PMP102 (20 decks)

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