Pharmacology: Skin as Route of Drug Administration

Question 1

what are the major routes of drug administration to the skin

Answer 1

topical, transdermal, subcutaneous

Question 2

what other epithelial drug routes are there other than the major ones

Answer 2

airways, conjunctival sac, nasal mucosa, vaginal

Question 3

of the major epithelial drug routes, what route(s) of administration are largely used for local effect and what type(s) are used for systemic effect

Answer 3

local effect = largely topical drugs

systemic effect = transdermal and subcutaneous

Question 4

describe what topical drug administration involves

Answer 4

drug, dissolved in lotion, cream etc., applied to skin surface where is diffuses to underlying layers of the skin to exert effect

Question 5

describe what transdermal drug administration involves

Answer 5

drug diffuses across skin and subsequently enters dermal capillaries for distribution to body tissues and organs

Question 6

describe what subcutaneous drug administration involves

Answer 6

skin is bypassed by drug, in a small volume of vehicle, being injected directly into the fat between skin and muscle

Question 7

describe what the stratum corneum is

Answer 7

it is the single most important barrier to drug penetration into the skin, or diffusion across it

Question 8

what does the stratum corneum consist of

Answer 8

corneocytes(hardened, dead keratinocytes) surrounded by intercellular lipids forming 10-30 sheets of tissue that are constantly shed and renewed

Question 9

describe the ‘bricks’ part of the ‘bricks and mortar’ model of the stratum corneum

Answer 9

corneocytes are highly cross linked by protein ‘rivets’ providing tensile strength

Question 10

describe what corneocytes are made up of

Answer 10

keratin macrofilaments embedded in a filaggrin matrix surrounded by a cornified cell envelope

Question 11

describe the ‘mortar’ part of the ‘brick and mortar’ model of the stratum corneum

Answer 11

it refers to the multiple lamellar structures of intercellular lipids, they act as a largely hydrophobic ‘intercellular glue’ that can also act as a reservoir for lipid-soluble drugs

Question 12

describe drug delivery into and across the stratum corneum when a drug is applied topically

Answer 12

passive process, mediated by diffusion

Question 13

describe the delivery of a drug through the stratum corneum for local and systemic effects

Answer 13

requires movement into and through the stratum corneum, mainly via intercellular route allowing diffusion of small, hydrophobic, drugs