Transdermal System

Question 1

Stratum Corneum

Answer 1

The stratum corneum, being keratinized tissue, behaves as a semipermeable artificial membrane, and drug molecules penetrate by passive diffusion. It is the major rate-limiting barrier to transdermal drug transport.

Question 2

Paracellular pathway

Answer 2

via the lipid intercellular matrix

Question 3

Transcellular pathway

Answer 3

across keratinized cells

Question 4

Transappendageal pathway

Answer 4

across hair follicles and sweat ducts

Question 5

Benefits of Transdermal Drug Delivery

Answer 5

1. Controlled delivery rate into systemic circulation.
2. Substitute for oral administration.
3. Maintain efficacious plasma levels: 1 to 7 days.
4. More reliable and predictable blood levels.
5. Avoids first-pass metabolism.
6. Improved patient compliance, non invasive.
7. Increases efficacy and, typically, decreases toxicity

compared to oral delivery.

Question 6

Drug Candidates for TDD

Answer 6

1. Daily dose (< 20 mg/day)
2. Short half-life (nitroglycerin is 3 min)(reduce frequency of administration)
3. Molecular weight (< 500 Daltons)
4. Lipid solubility- partition coefficient
5. Non-irritating and non-sensitizing to skin.

Question 7

Limitations

Answer 7

• Only relatively potent drugs (usually less than 20 mg and ideally < 10 mg/day)
• Molecular size (<500 Dalton)
• Poor diffusion of large/hydrophilic molecules
• Skin irritation and contact dermatitis
• Lack of adhesiveness with certain TDDS
• Expensive

Question 8

Chemical Enhancers

Answer 8

1. Increases skin permeability by reversibly damaging or altering the physicochemical nature of the stratum corneum.
2. Interaction with cellular proteins.
3. Improved partitioning of drug co-enhancer or co-solvent into the stratum corneum.

Question 9

Non-ionic surfactants

Answer 9

Spans®, Tweens®, poloxamers

Question 10

Iontophersis (Physical)

Answer 10

delivery of charged chemical compound across the skin membrane using an electrical field.

Question 11

Sonophoresis (Physical)

Answer 11

a high frequency ultrasound influences the integrity of the stratum corneum and is used to enhance transdermal

drug delivery

Question 12

Electroporation (Physical )

Answer 12

cells are temporarily exposed to high intensity of electric pulse that leads to the formation of aqueous pores in the lipid bilayers of the stratum corneum

Question 13

Thermal Ablation (Physical)

Answer 13

heat is applied to the surface of the skin via laser or radiofrequency to deplete the stratum corneum at the site of heating, without damaging underlined epidermis

Question 14

Tape stripping (mechanical)

Answer 14

removing of the stratum corneum layers by repeated application of adhesive tape

Question 15

Microneedles (mechanical)

Answer 15

minimally invasive drug delivery system has a potential to be used as an alternative to hypodermic and SQ needle