Routes of Administration- Topical and Transdermal

Question 1

Why apply drugs to the skin? (3)

Answer 1

1. Skin surface treatment
2. Targeting of dermal layers (topical drug delivery)
3. Systemic delivery (transdermal drug delivery)

Question 2

How much % of human body weight is skin?
What is the SA of the skin?

Answer 2

15%
around 1.8 m2

Question 3

How do drugs permeate the skin?

Answer 3

Permeation occurs directly across the STRATUM CORNEUM which is also the main barrier to drug delivery via this route

(not via sweat ducts/hair follicles/sebaceous glands)

Question 4

Drug factors of permeation: (3)

Answer 4

• The drug needs to have an intermediate partition
  coefficient, i.e. not too polar, not too non-polar
• If it is a weak acid or a weak base then it should be in the unionised form
• Low molecular weight (<500 Daltons)

Question 5

Formulation factors of permeation:

Answer 5

• Drug concentration in formulation – maximum “flux”
  exhibited when vehicle is saturated
• Occlusivity promotes drug penetration
• Leads to skin hydration
• Ointments versus creams / gels
• o/w versus w/o creams
• Release from the vehicle – drugs
  (solutes) held firmly in the
  formulation exhibit low fluxes
• Presence of cosolvents and/or penetration enhancers

Question 6

Biological (human) factors that affect permeation: (4)

Answer 6

genitals > head & neck > trunk > arm > leg

• Age – dermis not fully mature until 3 to 6 months’ old
• Race – stratum corneum water content varies
• Skin condition (injury, disease)
• Natural variation between individuals

Question 7

What are the layers of the skin in order? (6)
- from top to bottom

Answer 7

1. stratum corneum
2. stratum lucidium
3. stratum granulosum
4. stratum spinous
5. stratum basale
6. Dermis (epidermis, dermis, hypodermis)

Question 8

Atopic Eczema causes damage to the..? which reduces its ability to..?

What is the first line of treatment?
Examples of treatment?

Answer 8

• Atopic eczema presents as a dry, scaly rash.
• Damage to the stratum corneum reduces its ability to prevent water loss
• Emollient preparations are first
  line for treatment of dry scaly skin
  conditions
• Doublebase and Diprobase

Question 9

What is the formulation of Doublebase?

Answer 9

• Doublebase tm contains the oily
  ingredients, isopropyl myristate and liquid paraffin in a gel-type formulation

Isopropyl myristate 15% w/w
Liquid paraffin 15% w/w

Question 10

What are carbomers?

Answer 10

Carbomers are synthetic high-molecular-weight crosslinked polymers of polymers of acrylic acid.

Question 11

What is a suitable treatment for most bites in adult patients?
Do insect bites usually need treatment?
What can result from insect bites and lead to patients wanting OTC treatment?

Answer 11

Hydrocortisone 1% OR Clobetasone
* Insect bites are typically harmless and resolve without treatment
* Erythema (rash/redness) and oedema (swelling) can be problematic for some and may warrant OTC treatment

Question 12

What is Hc45?
What does it treat?
What is the clinical advice?

Answer 12

Hydrocortisone acetate cream (1% w/w)
Eczema, Dermatitis and Insect bites

• Use sparingly on small skin areas, 1-2 times a da TWICE a day for a max of 7 days
• Do not cover with a dressing, Do not use in pregnancy, Do not use use on eyes, face, anal or genital areas, on broken or infected skin,

Question 13

Why is the advice given to “Use sparingly” or “Apply thinly”?

Answer 13

The drugs could be absorbed into the stratum basale and reach blood vessels and so be absorbed into the bloodstream

Question 14

What is a transdermal route NRT used to treat smoking cessation?
How long are they applied for?
What is an important factor to understand before choosing this treatment?

Answer 14

Transdermal patches (NRT)
*16-24h long term effect,
*Helps to reduce morning cravings
* Important to understand the patient’s smoking habits

Question 15

Topical formulations are typically used to treat…
whereas transdermal formulations are used for…

Answer 15

Skin conditions
A systemic effect