Pharmacology and the skin

Question 1

What are the major drug routes involved in the skin?

Answer 1

Topical (local effects)

Transdermal
Subcutaneous
Depot
systemic effects

Question 2

What is the most important barrier to drug penetration of the skin? What constituent of drug vehicles improves drug penetration, and what is the drawback of using it?

Answer 2

Stratum corneum

High lipid content e.g. ointment- messy/greasy, may affect compliance

Question 3

How do the following affect the topical absorption of a given drug:

a) nature of the skin
b) nature of the drug preparation

Answer 3

a) Thickness (stratum corneum); hydration; integrity of epideris
b) The vehicle; the drug salt (e.g. for hydrocortisone); the drug concentration and physical/chemical properties

Question 4

How does a drug delivered subcutaneously gain systemic dissemination?

Answer 4

Either by entry into capillaries or lymphatics (slow)

Question 5

What are the advantages of subcutaneous administration?

Answer 5

Relatively slow to absorb; quick; relatively painless; suitable for absorption of proteins/oil based drugs

Question 6

What are the disadvantages of the subcutaneous route?

Answer 6

Delivery volume is limited; possible inflammation, leakage, allergic reaction

Question 7

How is transdermal delivery usually achieved? What are the advantages/disadvantages?

Answer 7

Drug incorporated into adhesive patch applied to the epidermis
Avoidance of first pass metabolism, painless, convenient (increases compliance)
Only suitable for a small number of drugs (nicotine, GTN, estradiol)

Question 8

Describe how steroid hormones work (generally)

Answer 8

Lipophilic- cross membrane by diffusion.
Bind to receptors within cell membrane.
Movement to the nucleus.
Steroid-receptor complex binds to DNA at specific sequence elements