Pharmacology and the Skin

Question 1

Name the 2 routes of drug administration in the skin that are for systemic effect

Answer 1

Transdermal

Subcutaneous

Question 2

Give an advantage of topical drugs

Answer 2

allow a high conc of drug to be used but minimise systemic effects

Question 3

What part of the skin is the most important barrier to drug penetreation

Answer 3

keratin layer (stratum corneum)

Question 4

How is the keratin layer arranged?

Answer 4

coreneocytes containing keratin are held together by corenodesmosomes in a matrix of filaggrin

Question 5

How does the keratin layer act as a reservoir for lipid soluble drugs?

Answer 5

Contains a lot of intercellular lipids eg cholesterol and free fatty acids making it very hydrophobic

Question 6

How is the choice of topical medication determined?

Answer 6

physicochemical properties of the drug,

the clinical condition

Question 7

How do you work out the rate of absorption o a drug

Answer 7

permeability coefficient (Kp) x conc of drug in vehicle (Cy)

Question 8

What combo of hydrophilic/phobic and lipophilic/phobic properties of the vehicle would ensure its fastest movement across keratin layer?

Answer 8

lipophilic drug in a hydrophilic base

Question 9

What combo of hydrophilic/phobic and lipophilic/phobic properties of the vehicle would cause its slowest movement across keratin layer?

Answer 9

lipophilic drug in a lipophilic base

Question 10

Why are topical drugs generally poorly absorbed?

Answer 10

only a small amount manages to get into the keratin layer

Question 11

what would improve the success of a topical drug getting into the keratin layer and why?

Answer 11

hydration via fatty cream or cling film as they prevent H2O loss from skin, allowing it to hydrate keratin layer and thus make it more permeable to drugs

Question 12

Least permeable areas of topical application?

Answer 12

nails, palm, sole

Question 13

which is more potent:

1% hydrocortisone or 0.1% hydrocortisone

Answer 13

0.1%

Question 14

side effects of consistent potent steroid application

Answer 14

steroid rebound, 
skin atrophy,
infection,
rosacea,
stretch marks