Transdermal And Topical Drug Delivery Flashcards
What are there disadvantages of transdermal drug delivery?
Only suitable for drug molecules with specific physicochemical properties that do not harm the skin. (Drugs must be potent but non irritant)
Intra and inter variabiltiy associated with the permeability of intact and diseased human skin.
Dermal metabolism
Skin irritation and sensitisation
Technical difficulties in adhesion
Skin is a strong barrier for drug absorption
What are the advantages of transdermal drug delivery?
Avoids chemically hostile GI environment Avoids first pass metabolism Reduced side effects Reduced drug dosing (controlled release) Easy to administer / painless Better patient adherence Direct targeting of tissue Rapid termination
What are the main functions of the skin?
Protection against external stimuli Heat regulation Water resistance Control of evaporation Storage and synthesis
What are the three main layers of the skin?
Epidermis, dermis, hypodermis
What are the components of the epidermis?
Stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum, stratum basale
What are the components of the dermis?
Sebaceous gland, sweat duct, sweat gland, blood vessels,
Fibrous proteins, glycosaminoglycans, lymphatic vessels, hair follicles
What are the components of the hypodermis?
Lymphatic vessels, fat globules
What are the components of the stratum corneum?
Cornified cell envelope which surrounds each corneocyte. (Like an oval)
Cormeodesmosome which connects corneocytes together.
Natural moisturising factor inside the corneocytes
Extracellular lipid (kind of like background)
Stratum granulosum which supports the corneocytes
What is the stratum corneum?
The uppermost layer of the skin.
Main barrier to drug transport as it is very dense
Consists of terminally differentiated keratinocytes (now known as corneocytes) 10-15 layers
Where are corneocytes embedded?
Into the lipid rich bilayer called mortar, in the stratum corneum
What is the function of corneocytes?
They protect the skin from physical and chemical damage
What are the two main parts of the epidermis?
Viable epidermis (consists of live cells) And inviable epidermis (consists of dead cells)
What makes up the viable epidermis?
Stratum basale
Stratum spinosum
Stratum granulosum
Stratum lucidum
What to makes up the inviable epidermis?
Stratum corneum
What is the dermis?
3-5mm thick
Functions to cushion, stretch and strength
Provides nutritional support to the epidermis
Also involved in metabolism/synthesis
What are the permeation pathways for a transdermally delivered drug?
Drug is released from the device, travels into stratum corneum, and partitions and diffuses into the subcutanesous layer.
It then diffuses into the viable epidermis which is a metabolic site, here some of the drug molecules will reach a receptor, while others will continue to partition into the dermis.
The dermis is another metabolic site, drugs here will reach another receptor and will also be removed systemically and lymphatically.
Drugs removed systemically will then partition and depot into fat tissue