This document discusses percutaneous absorption, which is the absorption of drugs through the skin. It describes the structure of skin, which consists of the epidermis and dermis layers. Percutaneous absorption involves drugs diffusing through the stratum corneum barrier and into the skin microcirculation. The rate of absorption is affected by factors like the drug's physicochemical properties, skin conditions, and techniques used to enhance delivery like hydration, ultrasound, or chemical enhancers. The goal is to maximize bioavailability by overcoming the stratum corneum barrier through various approaches.

1. Percutaneous absorption
Ms.Wajiha Iffat
Objective:
After the end of this lecture, student will be able
to :
•Describe Structure of skin
•define the percutanous absorption
•Its importance
•Factor affecting percutaneous absorption
•Ways to maximize drug bioavailibility

2. Percutaneous Absorption
• Skin also known as cuteneous membrane or
integument .
• 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-
0.08in).

3. Percutaneous Absorption
• In adults, the skin covers an area of about 2
square meter and weight 4.5-5kg, about 16%
of total body weight.

6. Percutaneous Absorption
• Skin is made up of two layers,
1.Outer epidermis,
2.Inner dermis.
• 1:-Epidermis
epi =above , dermis=skin
• It is the superficial , thinner portion
composed of keratinized stratified squamous
epithelial tissue.

7. Percutaneous Absorption
• Epidermis replaces itself . about every two and
half months.
• It has no blood vessel but it is nourished by
diffusion of nutrients from a vascular network of
dermis.
• It is composed of 4 type of cells
1-keratinocytes
2-melanocyets
3-langerhans cell
4-merkel cell.

8. Percutaneous Absorption
keratinocytes
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.
Melanocytes
Melano=black, cytes=cell
• 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
light

9. Percutaneous Absorption
Langerhans cells
• 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.
Merkel cell
• Participate in detection of touch sensation.

10. Percutaneous Absorption
DERMIS :
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
temperature regulation.

11. Percutaneous Absorption
Hypodermis :
• Below the dermis is hypodermis also k/as
subcutaneous layer
• Sub mean under and cutaneous mean skin.
• It is a loose layer of connective tissue which is
anchored to the underlined tissue ( muscle and
bones).
• 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

12. Percutaneous Absorption
Appendages of the skin:
• Hair follicles with hair
• Nails
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
of adolescense.

13. Percutaneous Absorption
Percutaneous Absorption:
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
molecules

14. Percutaneous Absorption
• 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
TDDS TRANSPORT.

15. Percutaneous Absorption
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
absorption

16. Percutaneous Absorption
FACTOR AFFECTING PERCUTANOUS
ABSORPTION:
BIOLOGICAL PARAMETERS:
• Skin condition
• Skin age
• Blood flow
• Regional skin sites
• Skin metabolism

17. Percutaneous Absorption
PHYSICOCHEMICAL PARAMETERS:
• Physicochemical Attraction Of Drug
• Mol Wt Of Drug
• Hydration Of Skin
• Temperature & pH
• Drug Concentrations
• Diffusion coefficient
• Partition coefficient
• Area Of Applications
• Contact Time

18. Percutaneous Absorption
MAXIMIZING THE BIOAVAILIBILITY OF DRUG TO
SKIN:
• Drug or pro drug selection
• Hydration
• Ultrasounds(phonophoresis)
• Ionophoresis
• elctroporation
• Stratum corneum removal
• Microneedle array
• Chemical penetration enhancers