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PMP102 - Drugs and Medicines > surfactants and suspending agents > Flashcards

surfactants and suspending agents Flashcards

1
Q

How is surface tensionn problematic in pharmaceutics?

A
  • Wetting process hindered if surface tension too high
  • Add surfactant molecules to replace some of the water
    molecules in the surface
  • Forces of attraction between surfactant and water
    molecules are less than those between two water
    molecules, hence the contraction force is reduced
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2
Q

What is a surfactant molecule?

A
  • An amphiphilic/amphipathic molecule that consists of a distinct hydrophobic and
    hydrophilic region
  • A molecule that accumulates at interfaces
  • A molecule that aggregates or self-assembles
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3
Q

What are some pharmaceutical applications of surfactants?

A
  • Surfactants are present in suspensions and emulsions
  • Aggregated surfactants can be used as drug delivery vehicles: e.g.
    micelles and vesicles to solubilise insoluble drugs
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4
Q

How do surfactants work?

A
  • Adsorption at the oil-water interface lowers interfacial tension
  • Aids the dispersal of the oil into droplets of a small size
  • Maintains the particles in a dispersed state
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5
Q

What are the two types of surfactants?

A
  • ionic surfactants
  • non ionic surfactants
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6
Q

What are some properties of ionic surfactants?

A
  • Anionic (dissociate at high pH) and
    cationic (dissociate at low pH)
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7
Q

What are some properties of non-ionic surfactants?

A
  • Widely used, less toxic and irritant
    than ionic surfactants
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8
Q

What happens if you mix the two types of surfactants?

A
  • Produce more stable emulsions
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9
Q

What are the classification of surfactants?

A

*anionic
*cationic
*non-ionic
*zwitterionic

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10
Q

What are the properties of anionic surfactants?

A

negatively charged surfactant, positive counterion
* Sodium dodecyl sulfate (SDS) (aka sodium lauryl sulfate, SLS)
* Freely soluble in water
* Forms self-emulsifying bases with fatty alcohols
* Detergent in medicated shampoos
* Skin cleanser in topical applications

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11
Q

What are some properties of cationic surfactants?

A

positively charged surfactant, negative counterion
* Cetylpyridinium chloride (quaternary ammonium/pyridinium)
* Freely soluble in water
* Has antimicrobial activity – cleaning of wounds, contaminated utensils,
preservative
* Enhance transdermal drug delivery preparations

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12
Q

What are some properties of nonionic surfactants pt2?

A

*uncharged
* spans = sorbitan fatty acid esters
* tweens/polysorbates = polyoxyethylene sorbitan fatty acid esters

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13
Q

What are zwitterionic surfactants?

A
  • two charges
  • overall neutral
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14
Q

What other types of surfactants are there?

A

*drugs
*naturally occuring:
- bile salts
- lecithin
- synovial fluid
- lungs surfactant

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15
Q

What do co-surfactants do?

A

To achieve very low interfacial tension, a second amphiphile (co-
surfactant) is incorporated
* Usually short chain alcohols or amines ranging from C4 to C10
* Helps in the formation and stabilisation of micelles/microemulsions
* Increases the flexibility and fluidity of the interface
* covers entire water droplet

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16
Q

What are the 3 types of co-surfactant/ surfactant mixture?

A
  • cetrimide emulsifying wax
  • emulsifying wax
  • non-ionic emulsifying wax
17
Q

What are micelles?

A
  • Colloidal spherical or near spherical nanoparticles
  • Loose aggregates of 50 – 100 surfactant molecules into a single entity
  • Size of micelles ~ 5 – 10 nm
18
Q

What are some properties of micelles?

A
  • Micelles are dynamic structures
  • Individual monomers may enter or leave the micelles = rapid process
  • Micelles are constantly breaking down and reforming = slow process
19
Q

Describe surfactant self assembly with micelles?

A
  • 60 randomly positioned molecules of
    polysorbate 80 first aggregate into small
    clusters, which then come together to form a
    single micelle
  • The micelle then undergoes restructuring to
    yield its final equilibrium arrangement
20
Q

Describe micelle formation in water in terms of dispersion of lipids in water, clusters of lipid molecules
+ micelle

A
  • Dispersion of lipids in water
  • Each lipid molecule forces surrounding water
    molecules to become highly ordered
  • Clusters of lipid molecules
  • Only lipid portions at the edge of the
    cluster force the ordering of water. Fewer
    water molecules are ordered, and entropy is
    increased
  • Micelles
  • All hydrophobic groups are sequestered
    from water, no highly ordered shell of water
    molecules is present, and entropy is
    increased
21
Q

What are the thermodynamics like in micelle formtion of water?

A

Micelle formation results in an increase in
entropy because water molecules regain
their freedom upon micellization (i.e. loss of
the cage structure)

22
Q

How does water interact with hydrophilic head groups?

A
  • Water molecules interact with
    surfactant headgroups
  • Polyethylene glycol
  • Carboxylate groups
  • Head groups start to repel each other
    if brought in too close in contact →
    stops micelles from growing
23
Q

How does repulsive forces differ between non ionic surfactant head groups and ionic surfactant head groups?

A

ionic: strong repulsion = small micelles
non ionic: less strong repulsion = large micelles

24
Q

What is CMC?

A
  • critical micelle concentration
  • The surfactant concentration at and above which micelles are formed
  • Determined by measuring the surface tension at different [surfactants]
25
Q

What is the surface tension like above the CMC?

A
  • the surface tension of the solution above the CMC is constant
26
Q

What is osmotic pressure like for the CMC?

A
  • Osmotic pressure depends on the no. of molecules present in water, tailed
    off after CMC
27
Q

What is conductivity like with the CMC?

A
  • At CMC, this abruptly causes the concentration of the current carrier
    anions to decreases
28
Q

What is light scattering like (CMC)?

A
  • Intensity of scattered light between free surfactant monomers and
    micelles
    (above CMC)
29
Q

What is drug solubilisation like (cmc)?

A
  • Micellar solubilisation only occurs above the CMC
30
Q

What is an application of micelles?

A
  • Micellar solubilisation
  • Process whereby a material insoluble in water (e.g. a poorly soluble
    drug) can increase its ‘apparent’ solubility by being incorporated into
    a micelle (dissolve in the hydrophobic environment of the micelle)
31
Q

What are the sites of solubilisation?

A

Several possible sites of solubilisation:
a) Hydrocarbon core
* Non-polar solubilisate
b) Core/mantle region
* Amphiphilic solubilisate
c) Head group (mantle) region
* More polar solubilisate
d) Surface adsorption
* Polar solubilisate on the shell

32
Q

What are suspending agents for?

A
  • To reduce the rate of settling of suspended active ingredients
  • Increases the viscosity of the suspension
  • Drugs can be readily and uniformly resuspended before use
33
Q

What are some examples of suspending agents?

A
  • Polysorbate
  • Methylcellulose
  • Povidone
  • Xanthan gum
  • Carbomer
34
Q

What is the ideal suspending agent?

A
  • Readily and uniformly incorporated into formulation
  • Readily dispersed in water without special techniques
  • Ensure the formation of a loosely packed system which does not cake
  • Does not influence the dissolution rate or absorption rate of the drug
  • Be inert, non-toxic and free from incompatibilities

PMP102 - Drugs and Medicines (20 decks)

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