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PHRM 100 – PDD > PDD 06 and 07: Dispersions > Flashcards

PDD 06 and 07: Dispersions Flashcards

1
Q

What are coarse dispersions?

A

particle size for dispersed phase is 10-50 μm

  • suspensions
  • emulsions
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2
Q

What are fine dispersions?

A

particle size for dispersed phase is 0.5-10 μm

  • gels
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3
Q

What are the clinical concerns for dispersions?

A

needs to be homogeneous for accurate dosing

  • solid particles in suspensions tend to settle to bottom due to increased density
  • how about O/W emulsions**
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4
Q

What are suspensions?

A

preparations containing finely divided drug particles distributed uniformly in a vehicle in which the drug exhibits low solubility

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5
Q

What are the two phases of a suspension?

A
  • dispersing phase: water-based
  • dispersed phase: solid drug particles

–––––

  • ie. tylenol: preparation in liquid form
  • ie. amoxicillin: preparation in dry powder form – reconstituted with water before use
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6
Q

What are the two phases of emulsions?

A
  • dispersing phase: water-based
  • dispersed phase: liquid oil based
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7
Q

What are the advantages of a suspension? (4)

A
  • increased stability compared to solutions
  • ease of swallowing compared to solid dosage forms
  • flexibility in administration of a range of doses
  • improved palatability compared to solutions
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8
Q

How do we ensure accurate dosing of a suspension? (3)

A
  • suspension should settle slowly and should be readily re-dispersed upon gentle shaking of container
  • particle size of suspension should remain fairly constant throughout long periods of undisturbed standing
  • suspension should pour readily and evenly from its container
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9
Q

What are some important considerations for suspensions for patients?

A
  • formulations for infants
  • storage
  • shaking before dosing
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10
Q

What should we consider for infants in regards to suspensions? (2)

A
  • should not contain preservatives, alcohol, and propylene glycol
  • flavouring agent is not required
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11
Q

How should suspensions be stored?

A
  • air-tight, light-resistant container
  • refrigerator
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12
Q

What is Stoke’s law?

A

sedimentation of particles in a suspension

dx / dt = D2 (ρi- ρe)g/18η

  • Dx/dt: rate of sedimentation
  • D: diameter of particles
  • ρi and ρ: density of particles and medium
  • g: gravitational constant
  • η: viscosity of medium
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13
Q

Why can’t viscosity of suspensions be too high?

A

to prevent easy pouring and re-dispersion of the suspension

  • should avoid reducing particle size too much because fine particles have a tendency to form a compact cake upon settling to the bottom of the container
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14
Q

What are flocculating agents?

A

form ‘bridges’ between particles

  • pH adjustments – reduce drug solubility
  • ie. clays – bentonite
  • ie. electrolytes
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15
Q

What are the 2 types of emulsions?

A
  • water in oil (W/O): ie. salad dressing
  • oil in water (O/W): ie. milk
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16
Q

What are water in oil (W/O) emulsions?

A
  • dispersing phase: oil-based
  • dispersed phase: water-based
  • emulsifying agents at interface
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17
Q

What are oil in water (O/W) emulsions?

A
  • dispersing phase: water-based
  • dispersed phase: oil-based
  • emulsifying agents at interface
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18
Q

What is a dispersing phase?

A

external phase or continuous phase

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19
Q

What is a dispersed phase?

A

internal phase

20
Q

How can you determine the emulsion type?

A

use dilution test (add drops of water)

  • O/W: water distributes uniformly
  • W/O: water collects at bottom
21
Q

Describe the appearance of emulsions.

A

depends on formulation:

  • liquid – oral, topical, parenteral (ie. milk)
  • semi-solid – topical only (ie. facial cream)
22
Q

What are the two major theories of how emulsifiers are stabilized?

A
  • interfacial film
  • oriented-wedge (monolayer) surfactants
23
Q

Interfacial Film

A

emulsifiers sit at interface of water and oil (O/W), forming barrier to prevent aggregation or fusion of oil droplets

  • carbohydrates: acacia, agar (O/W)
  • proteins: gelatin, egg yolk (O/W)
  • finely divided solids: bentonite, magnesium hydroxide
24
Q

Oriented-Wedge (Monolayer) Surfactants

A

(O/W) polar head sticking out to water, fatty chain sticking out to oil – also forming barrier between water and oil to prevent aggregation and fusion

  • high molecular weight alcohols: cetyl alcohol, stearyl alcohol
  • phospholipids: lecithin
  • anionic: surfactants triethanolamine oleate, sodium lauryl sulphate
  • cationic surfactants: cetylpyridinium chloride (antibacterial)
  • nonionic surfactants: sorbitan esters and polyethylene derivatives, such as Span and Tween
25
Q

Oriented-Wedge (Monolayer) Surfactants

Can you combine anionic and cationic surfactants/agents?

A

no

26
Q

What are emulsifiers selected based on? (5)

A
  • compatibility
  • stable
  • non-toxic (maybe dose-dependent)
  • little odour, taste, or colour
  • most importantly, should promote emulsification and maintain stability of the emulsion
27
Q

Describe the physical instability of emulsions. (4)

A
  • dispersed phase forms aggregates of globules (flocculation or coalescence)
  • large aggregates rise to top or fall to bottom (creaming)
  • liquid of dispersed phase separates and forms a distinct layer (breaking)
  • phase inversion
28
Q

What is another instability of emulsions?

A

microbial contamination

29
Q

What law does the rate of separation of emulsion follow?

A

Stoke’s law

dx / dt = D2 (ρi- ρe)g/18η

  • Dx/dt: rate of sedimentation
  • D: diameter of particles
  • ρi and ρe: density of particles and medium
  • g: gravitational constant
  • η: viscosity of medium
30
Q

How can you increase the stability of emulsions? (3)

A
  • reduce size
  • minimize density difference
  • increase viscosity of medium – thickeners (ie. tragacanth, microcystalline cellulose)
31
Q

How can we improve emulsion stability? (6)

A
  • avoid extreme heat and cold
  • avoid freezing and thawing
  • minimal stability requirement: 3 months at 5-40ºC
  • light-resistant container
  • addition of antioxidant (ascorbic acid, vitamin E) – containers tightly closed to air after each use
  • antimicrobials
32
Q

Describe antimicrobial agents in emulsions.

A
  • fungi contamination dominates, and normally occurs in water phase
  • methylparaben, propylparaben or 12-15% alcohol is included in aqueous phase
33
Q

What are the 4 types of physical instability of emulsions?

A
  • coalescence
  • flocculation
  • creaming
  • breaking
34
Q

What is flocculation?

A

oil droplets are aggregating to each other, but not fusing

35
Q

What is coalescence?

A

fusion of oil droplets

36
Q

What is creaming?

A

after aggregation of oil droplets, oil droplets float to the top

37
Q

What is breaking?

A

oil and water are completely separated

38
Q

Coalescence, Flocculation, Creaming, and Breaking

Which are reversible (ie. shaking it will bring it back to a good emulsion)?

A
  • flocculation
  • creaming
39
Q

What is the function of acacia (finely powdered)?

A

(polysaccharide) emulsifying agent

40
Q

What is the function of syrup?

A
  • thickening agent
  • flavouring agent
41
Q

What is the function of vanilin?

A

flavouring agent

42
Q

What is the function of alcohol?

A

antimicrobial agent

43
Q

What are the advantages of an O/W emulsion compared to mineral oil only?

A
  • tastes better
  • absorbed better
  • overall more effective
44
Q

What is the function of mineral oil?

A

stimulate bowel movement (oil phase)

45
Q

Grace is preparing an O/W emulsion and has selected sodium lauryl sulfate as the major emulsifier. What does she need to know to avoid compatibility issues and how can she know whether the product is indeed O/W?

A
  • surfactant is anionic
  • don’t include another cationic emulsifier (precipitation)
  • dilution test – if O/W it should be very miscible
46
Q

Grace would like to improve the stability of her emulsions and asks for your advice. What would you suggest?

A
  • storage conditions – air-tight and light-resistant container, avoid extreme/cold and freeze/thaw
  • small particle formulation
  • increase viscosity
47
Q

What is the advantage of using a topical water-in-oil emulsion?

A

can prevent moisture loss from skin surface

PHRM 100 – PDD (14 decks)

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