Pharmacology: Pharmacology and the Skin Flashcards
Define topical drug administration
Drug in a pharmacologically inactive vehicle applied to the surface of the skin where it then diffuses though the skin and may be absorbed into the bloodstream
What are the ‘bricks’ in the ‘brick and mortar’ model of the stratum corneum?
Corneocytes containing keratin macrofilaments embedded in a filaggrin matrix surrounded by a cornified cell envelope
What is the function of the corneodesmosomes in the stratum corneum?
The corneodesmosomes are protein ‘rivets’ which crosslink the corneocytes to provide mechanical strength
What is the ‘mortar’ in the ‘brick and mortar’ model of the stratum corneum?
Multiple lamellar structures of intercellular lipids (mainly ceramides, cholesterol and free fatty acids)
What is the pharmacological relevance of the intracellular lipids in the stratum corneum?
Act a reservoir for lipid-soluble drugs e.g. topical corticosteriods
Describe the transcellular route of topical drug diffusion through the stratum corneum
Involves crossing the skin by directly passing through both the lipid structures of the interlamellar region and moving across corneocytes
Describe the intercellular route of topical drug diffusion through the stratum corneum
Drugs pass through the small spaces between the cells of the skin
This allows the movement of small, hydrophobic drugs into and through the stratum corneum
What is the transappendageal route of topical drug diffusion through the stratum corneum?
Certain drugs are able to penetrate the stratum corneum via the hair follicles and sweat glands
The rate of absorption of topically applied drugs follows which biological principle?
Fick’s Law of Diffusion
What factor provides the driving force for skin penetration of topical drugs?
The dissolved concentration of the drug in the vehicle (Cv)
How do excipients improve partitioning of a drug from the vehicle into the skin?
Including excipients which increase the solubility of hydrophobic drugs will enhance absorption
How does occlusion of the skin (e.g. cling film, use of ointment) improve partitioning of a drug from the vehicle into the skin?
Occlusion prevents water loss by evaporation, which hydrates the skin
Describe the mechanism of action of glucocorticoids
Activate a receptor in the cytoplasm that translocates into the nucleus which then switches on anti-inflammatory genes and switches off inflammatory genes
Define subcutaneous drug administration
Drug delivered by a needle inserted into the adipose tissue just beneath the surface of the skin
The drug reaches systemic circulation by diffusion into either capillaries or lymphatic vessels
Define transdermal drug delivery (TDD)
The drug is usually incorporated into an adhesive patch applied to the epidermis, and drug absorption is (partially) controlled by a drug release membrane - overcomes the limitation of the cutaneous barrier, but has all the advantages of topical drug application
