D.4 Transdermal Drug Delivery

Question 1

What is transdermal drug delivery?

Answer 1

Delivery of drug to the systemic circulation through the skin.

Question 2

What is the difference between topical drug delivery and transdermal drug delivery?

Answer 2

Topical is when the drug target is on the skin whereas drug target for transdermal is in the systemic circulation

Question 3

What are the advantages of transdermal drug delivery?

Answer 3

Avoidance of GIT (enzyme and pH)
Avoidance of first pass metabolism
The controlled rate of drug delivery
Reduced frequency of administration/dosing
REduced inter and intrapatient variability
Drug input readily terminated (removal of the patch)

Question 4

Why can only a few drugs be put in transdermal drug delivery?

Answer 4

Skin is an effective barrier

Few drugs are suitable for TDD

Question 5

What are the tree pathways through the stratum corneum?

Answer 5

Transappendageal
Transcellular
Intercellular (easiest to exploit)

Question 6

What factors affect drug absorption through the skin?

Answer 6

Skin condition (age, body site, hydration, pathological disorders)

Physiochemical properties of drug:

• MW
• Partition coefficient between vehicle and skin
• pKa
• Solubility in vehicle
• Concentration

Question 7

How are drugs delivered transdermally?

Answer 7

Gels/creams/ointments

transdermal patches

Question 8

What are the drawbacks of transdermal patches?

Answer 8

Skin allergy/irritation (alter sight of application)
Cannot be cut
Fragile
Still contains drug after use (safe disposal)
drug release rate increases with temperature
variability in designs, administration frequency, administration site (patients may get confused)

Question 9

How can you extend the range of drugs suitable for TDD?

Answer 9

Modification of the physicochemical properties of the drug
Pro-drug
Ion pairing

Optimization of the vehicle
Liposomes
Microemulsions
Heating patches

Avoidance/alterations of the stratum corneum