Transdermal patches

Question 1

Roles of the epidermis(stratum cornuem sits on top ) and dermis layer of skin

Answer 1

Dermis
➢Supplies epidermis with blood, lymphatic vessels and
nerve endings

Epidermis
➢Physiologically active tissues
➢Inactive stratum corneum

Stratum corneum
➢Abt 10-25 mm thick
➢Main barrier to entry of drugs
➢Retains body moisture

Question 2

2 different drug penetration ways

Answer 2

i. Appendageal route:
- going through the hair, sebaceous and sweat glands
ii. Epidermal route:
- Intracellular
right through to blood vessels
- Intercellular
going through tight junctions in the stratum corneum

Question 3

Factors affecting percutaneous absorption

Answer 3

• Area of application
• Length of application
• Skin factors:
  ➢Hydration
  ➢Thickness of horny layer
• Drug factors:
  ➢Partition coefficient
  ➢ Molecular weight
  ➢Concentration
  ➢Polar/non-polar

Question 4

Advantages of TDDS

Answer 4

By-pass chemically hostile GI environment and first
pass effect of liver
* Better plasma conc time
profile*
* Predictable and extended
duration of activity
* Increases patient compliance
* Reversibility of drug delivery which allows removal of
drug source

Question 5

Disadvantages of TDDS

Answer 5

• Cannot cut patches to half the dose
• Paediatric doses
• Only relative potent drugs are suitable for this route
• Issues with skin irritation (1-2%)
• Restricted area of application

Question 6

Basic components of TDDS.1
Backing, polymer matrix

Answer 6

Backing
➢ Chosen for appearance, flexibility and need for occlusion
➢ Additives don’t leach out into the drug reservoir
➢ Drug reservoir components don’t diffuse through the backing

• Polymer matrix
  ➢ Stable, non-reactive with the drug, easily manufactured and
  inexpensive.
  ➢ Should not deteriorate excessively when large amounts of active
  ingredient are incorporated
  ➢ Should be biocompatible and chemically compatible with other
  components of the system
  ➢ Should provide consistent and effective delivery of drug throughout
  the product’s life

Question 7

Basic components of TDDS.2
Adhesive layer and release liner

Answer 7

Adhesive layer
➢ Two types: peripheral adhesive or face adhesive
➢ Non-irritating, allow easy peel-off after use, permit unimpeded drug
flux to the skin and be compatible with all other components in the
system.
➢ Related to drug delivery and therapeutic effect
➢ Quality of bond between patch and skin directly reflects consistency of
drug delivered
➢ Poor adhesion results in improper dosing of patients

• Release liner
  ➢ Protective liner that is removed and discarded before the application
  ➢ Liner should be chemically inert

Question 8

Active penetration enhancement techniques

Answer 8

1. Iontophoresis (IP)
2. Sonophoresis
3. Microneedles