25/04/2023
Skin as a Route of Administration (PY4010)
Physiology and Transdermal Delivery Systems
The skin
Single largest organ in the human body. Skin serves a number of critical functions such as
protection and sensor.
The skin is divided into 3 layers - the epidermis, the dermis, and the subcutaneous fat layer.
Epidermis
Outermost layer of the skin. Epidermis is avascular. The thickness varies from 0.05-1.5mm.
Outermost portion (stratum corneum) is 10-15 µm thick and consists of dead, flattened cells
embedded in a lipid bilayer. These dead, flattened cells are composed of tough, fibrous
protein called keratin and are being continuously replaced by newer cells that migrate
upward.
Dermis
Thick layer consisting of connective tissue and responsible for length and flexibility of the
skin.
Located below the epidermis.
The dermis layer embeds nerve endings, hair follicles, sweat glands, and blood vessels.
Drug molecules that diffuse across the epithelium are distributed systemically because of the
rich vascular network in the dermis.
Subcutaneous tissue
Located below the dermis.
Helps to regulate body temperature and provides a protective padding to other organs, and
to muscles, bones, etc.
Advantages of skin as a route of administration
Easy to apply and monitor dose of the given drug.
Reasonably constant dosage can be maintained.
First-pass metabolism in the liver and GIT is avoided.
Controlled drug delivery.
Non-invasive.
Dosage may be stopped by removal of the delivery system.
Limitations of skin as a route of administration
Presence of rate-limiting stratum corneum.
Large molecules (over 500 Da) experience the barrier of the skin’s structure based on the
molecular weight of the drug.
Only relatively potent drugs are suitable for transdermal delivery.
Skin as a Route of Administration (PY4010)
Physiology and Transdermal Delivery Systems
The skin
Single largest organ in the human body. Skin serves a number of critical functions such as
protection and sensor.
The skin is divided into 3 layers - the epidermis, the dermis, and the subcutaneous fat layer.
Epidermis
Outermost layer of the skin. Epidermis is avascular. The thickness varies from 0.05-1.5mm.
Outermost portion (stratum corneum) is 10-15 µm thick and consists of dead, flattened cells
embedded in a lipid bilayer. These dead, flattened cells are composed of tough, fibrous
protein called keratin and are being continuously replaced by newer cells that migrate
upward.
Dermis
Thick layer consisting of connective tissue and responsible for length and flexibility of the
skin.
Located below the epidermis.
The dermis layer embeds nerve endings, hair follicles, sweat glands, and blood vessels.
Drug molecules that diffuse across the epithelium are distributed systemically because of the
rich vascular network in the dermis.
Subcutaneous tissue
Located below the dermis.
Helps to regulate body temperature and provides a protective padding to other organs, and
to muscles, bones, etc.
Advantages of skin as a route of administration
Easy to apply and monitor dose of the given drug.
Reasonably constant dosage can be maintained.
First-pass metabolism in the liver and GIT is avoided.
Controlled drug delivery.
Non-invasive.
Dosage may be stopped by removal of the delivery system.
Limitations of skin as a route of administration
Presence of rate-limiting stratum corneum.
Large molecules (over 500 Da) experience the barrier of the skin’s structure based on the
molecular weight of the drug.
Only relatively potent drugs are suitable for transdermal delivery.
