Transdermal Drug Delivery

Which layer of the skin is not an important barrier for transdermal drug delivery?

Subcutaneous layer

What are the functions of subcutaneous layer?

• Provides mechanical protection against physical shock

• insulates the body

• provides a store of high-energy molecules

• carries the principal blood vessels and verves to the skin.

Which skin layer is metabolically active?

The dermis

Why does the dermis layer require extensive vasculatures?

Has several appendages in particular nerve endings, hair follicles and sebaceous glands, and eccrine and apocrine sweat glands; also, for regulation of body temperature, wound repair, oxygen and nutrient delivery, and removal of waste products.

How the blood flow in the dermis layer provides the driving force for the drugs delivered trans-dermally?

Keeps the dermal concentration of most transdermally delivered drugs low, which in turn provides a concentration gradient from the outside of the body into the skin

Which layer limits the drug delivery through the skin?

The stratum corneum

How does drug concentration affect the percutaneous absorption?

amount of drug percutaneously absorbed increases with an increase in drug concentration

How does area of application affect the percutaneous absorption?

larger area, larger amount absorbed

How does the length of application time affect percutaneous absorption?

greater length, greater absorption

How does skin hydration affect percutaneous absorption?

greater hydration, greater percutaneous absorption

What is the ideal molecular weight for a drug to permeate through skin?

400 or less

What is the ideal partition co-efficient range for a drug to permeate through skin?

1-4

Chemical enhancers

Increases skin permeability by reversibly damaging or altering the physiochemical nature of the stratum corneum to reduce its diffusional resistance.

Why biologically active peptides are administered by injection?

They have rapid metabolism and poor absorption after oral delivery.

Why biological peptides poorly absorbed by transdermal route?

Large molecular size and ionic character and general impenetrability of the skin.

Which process showed promise for peptides and proteins to be delivered transdermally

Sonophoresis

What are the sequences of skin layers that the transdermal drug delivery systems follow to reach into the blood stream?

Stratum corneum → epidermis → dermis

How transdermal drug delivery systems avoid the deactivation by digestive system and liver enzymes?

 They avoid the first-pass effect.

How transdermal drug delivery system is advantageous over parenteral route though parenteral route also avoid first pass metabolism? 

Noninvasive, avoiding the inconvenience of parenteral therapy.

How transdermal drug delivery system is more patient compliant in terms of dose frequency?

 They provide extended therapy with a single application.

How drug therapy can be terminated rapidly in transdermal drug delivery?

By removal of the application from the surface of the skin.

Why relatively potent drugs are suitable for transdermal delivery?

The natural limits of drug entry imposed by the skin’s impermeability.

Why rotation of site of application location is important for transdermal drug delivery systems?

Allows skin beneath a patch to regain its normal permeability after being occluded and to prevent skin irritation.

When a skin site can be reused for transdermal drug delivery application?

Skins sites may be reused after a week.

What is the consequence of applying transdermal drug delivery systems on wet skin and oily skin?

Can accelerate drug permeation beyond the intended rate when on wet skin; oily skin can impair adhesion of the patch.

What are two reasons to avoid skin lotions at application site for transdermal drug delivery system applications?

Lotions affect skin hydration and can alter the partition coefficient between the drug and the skin.

For how long a transdermal drug delivery system should be pressed firmly against the skin site during application?

10 seconds

Upon removal why do you think the transdermal drug delivery system should be folded in half and then discard it?

Prevents it from being reused