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Management of Infection > Lecture 12B - Topical Administration (skin) > Flashcards

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
Q

What can be used to thicken gels?

A

PEG, carbomer, vegetable gums such as gum tragacanth, guar gum

26
Q

What might the liquid phase of gels be?

A

aqueous, alcoholic, solvent may evaporate

27
Q

Drug release of gels?

A

equivalent to that of a solution (unless binding of the drug to the polymer, or high viscous gel)

28
Q

Examples of a gel?

A

metronidazole gel for the treatment of rosacea

29
Q

What are creams made of?

A

2 phased emulsion

water in oil (w/o) or oil in water (o/w)

30
Q

What is the most common semi solid topical formulation?

A

creams

31
Q

Advantages of creams?

A

w/o emulsions less greasy than ointments
easier to apply

can be washed off the skin surface

32
Q

Disadvantages of creams?

A

less occlusive than ointments

less beneficial in dry skin conditions

33
Q

Examples of creams?

A

mupirocin, neomycin, fusidic acid

34
Q

Examples of solid formulatios?

A

spray powders

35
Q

What are spray powders?

A

hydrocarbon propellant to deposit powders on the skin surface

incorporate a volatile solvent (ethanol) that dissolves some drug prior to evaporation

36
Q

Examples of spray powders?

A

miconazole nitrate (fungal skin infections such as athlete’s foot

37
Q

Advantages of spray powders?

A

can be given directly to the site of infection and easy to repeat treatment

Management of Infection (36 decks)

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