Lecture 12B - Topical Administration (skin) Flashcards

1
Q

What is the skin?

A

a complex multilayered membrane

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2
Q

What is the stratum corneum?

A

the outermost layer of the skin, composed of 15-20 layers of flattened, keratinised cells

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3
Q

What is the principle barrier to drug delivery?

A

the stratum corneum

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4
Q

To be suitable for topical drug deliver, what should an antimicrobial drug be?

A

have a low MWt (<500Da)

be moderately lipophilic (log P between 1 and 4)

be effective at a low dose (<10mg/day)

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5
Q

What is passive diffusion modelled by?

A

Fick’s first law of diffusion

J= -D ΔC/ Δx

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6
Q

What do the components of Fick’s law stand for?

A
J = flux
D = diffusion coefficient 
C = concentration of diffusing drug 
x = distance
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7
Q

What should a topical formulation be?

A

stable, but allowing the drug to be released following application

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8
Q

What should the vehicle of topical formulation allow?

A

some solubility of the drug, but should not retain the drug by being a very good solvent

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9
Q

What are the types of topical formulation?

A

liquid formulations

semi solid formulations

solid formulations

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10
Q

What are liquid formulations?

A

single phase solutions and lotions

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11
Q

Advantages of liquid formulations?

A

rapid short term input of permeant into the skin

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12
Q

Disadvantages of liquid formulations?

A

poor residence time on the skin which means low drug delivery

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13
Q

What happens to liquid formulations after application on the skin?

A

evaporation of the solvent (alcoholic vehicles)

cool, soothing effect on the skin

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14
Q

Examples of liquid formulations?

A

erythromycin solution, clindamycin lotion

treatment of acne

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15
Q

Semi solid formulation examples?

A

ointments, gels, creams

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16
Q

Advantages of semi solid formulations?

A

good residence time on the skin

good acceptance from the patients

17
Q

What are semi solid formulations?

A

drug in semi solid base (either hydrophobic e.g. liquid paraffin, glycerides, waxes or hydrophilic e.g. PEG)

18
Q

What does the base determine?

A

the release of the drug from the formulation

19
Q

What are ointments?

A

hydrophobic, fatty preparations

20
Q

Advantages of ointments?

A

highly occlusive

increase of transdermal flux
prolonged drug delivery

21
Q

Disadvantage of ointments?

A

messy to use and difficult to wash

22
Q

What are ointments used on?

A

dry lesions

23
Q

Examples of ointments?

A

mupirocin, fusidic acid (impetigo caused by staph infections)

24
Q

What are gels?

A

preparations formed from a liquid phase that have been thickened with other components

25
What can be used to thicken gels?
PEG, carbomer, vegetable gums such as gum tragacanth, guar gum
26
What might the liquid phase of gels be?
aqueous, alcoholic, solvent may evaporate
27
Drug release of gels?
equivalent to that of a solution (unless binding of the drug to the polymer, or high viscous gel)
28
Examples of a gel?
metronidazole gel for the treatment of rosacea
29
What are creams made of?
2 phased emulsion water in oil (w/o) or oil in water (o/w)
30
What is the most common semi solid topical formulation?
creams
31
Advantages of creams?
w/o emulsions less greasy than ointments easier to apply can be washed off the skin surface
32
Disadvantages of creams?
less occlusive than ointments less beneficial in dry skin conditions
33
Examples of creams?
mupirocin, neomycin, fusidic acid
34
Examples of solid formulatios?
spray powders
35
What are spray powders?
hydrocarbon propellant to deposit powders on the skin surface incorporate a volatile solvent (ethanol) that dissolves some drug prior to evaporation
36
Examples of spray powders?
miconazole nitrate (fungal skin infections such as athlete's foot
37
Advantages of spray powders?
can be given directly to the site of infection and easy to repeat treatment