After the end of this lecture, student will be able
•Describe Structure of skin
•define the percutanous absorption
•Factor affecting percutaneous absorption
•Ways to maximize drug bioavailibility
• Skin also known as cuteneous membrane or
• It means any external membranous covering
or integument of an animal body.
• Skin is the largest organ of the body ,it is thin
at some places (eye lids thickness =0.5mm)
where as thick at other places (sole of foot,
palm of hand thickness=5mm).
• Average thickness of skin is 1-2mm.(0.04-
• In adults, the skin covers an area of about 2
square meter and weight 4.5-5kg, about 16%
of total body weight.
• Skin is made up of two layers,
epi =above , dermis=skin
• It is the superficial , thinner portion
composed of keratinized stratified squamous
• Epidermis replaces itself . about every two and
• It has no blood vessel but it is nourished by
diffusion of nutrients from a vascular network of
• It is composed of 4 type of cells
keratino=horn like, cytes=cell
• 90% of epidermal cells are keratinocytes.
• These are arrange in 4 to 5 layers and are responsible for
production of protien keratin,which is a tough fibrous protein
responsible to protect the skin and underlying tissues from heat,
microbes and chemical.
• 8%of epidermal cells are melanocytes.
• They produces a pigment melanin (a yellow red or black brown
pigment) contribute in skin colour and also absoorbs damaging u-v
• They participate in immune responses against
microbes that invade the skin and they are
easily damaged by u-v light.
• Helps other cells of immune system to
recognize an invading microbe and destroy it.
• Participate in detection of touch sensation.
The sensitive connective tissue layer of the skin located
below the epidermis, containing nerve endings, sweat
and sebaceous glands, and blood, hair follicles,
fibroblast , histocytes and lymph vessels. Also called
corium, cutis, Also called derma.
• Composed of strong connective tissue containing
collagen ( for strength ) and elastin ( for stretch )
• Derma blood vessels not only supply blood to the
dermis and epidermis but also play major role in
• Below the dermis is hypodermis also k/as
• Sub mean under and cutaneous mean skin.
• It is a loose layer of connective tissue which is
anchored to the underlined tissue ( muscle and
• Most fats cells are present in hypodermis
collectively known as adipose tissues act as
insulator to protect the body from excessive heat
and cold environment
Appendages of the skin:
• Hair follicles with hair
Glands of skin:
• There are two types of glands
• Sweat glands
• Sebaceous glands
Sebaceous glands :
• They are simple or branched alveolar glands situated in the
dermis of skin
• They secrete an oily secretion c/as sebum active at the time
Percutaneous absorption involves the transfer
of drug from skin surface in to stratum
corneum, under the aegis of a concentration
gradient and its subsequent diffusion through
the dermis and in to microcirculation the skin
behaves as a passive barrier to diffusing
• Percutaneous absorption of a drug generally
results from the direct penetration of the drug
through stratum corneum,10-15µm thick layer
of flat partially desiccated non living tissues.
• SC is composed of 40%protein & 40%water
with a balance being lipid.
• SC acts as a semi permeable membrane &
drug molecules penetrates by passive
diffusion. it is the most rate limiting barrier to
RATIONAL APPROACH TO DRUG DELIVERY TO &
VIA THE SKIN:
• Surface treatment
• Strarum corneum treatment
• Skin appendage treatment
• Viable epidermis & dermis treatment
• Systemic treatment via transdermal
FACTOR AFFECTING PERCUTANOUS
• Skin condition
• Skin age
• Blood flow
• Regional skin sites
• Skin metabolism
• Physicochemical Attraction Of Drug
• Mol Wt Of Drug
• Hydration Of Skin
• Temperature & pH
• Drug Concentrations
• Diffusion coefficient
• Partition coefficient
• Area Of Applications
• Contact Time
MAXIMIZING THE BIOAVAILIBILITY OF DRUG TO
• Drug or pro drug selection
• Stratum corneum removal
• Microneedle array
• Chemical penetration enhancers