dds transdermal

skin components (3)

1. epidermis

2. dermis

3. subcutaneous layer

types of skin preparations (4)

1. liquid (external) —> liniment, aerosol spray

2. semi solid —> cream/ ointment

3. solid —> dusting powder

4. device —> dermal patches/ transdermal patches

what is transdermal patch

its is a medicated adhesive path that delivers drugs thru the skin and into the bloodstream

MOA of transdermal patch

• delivers drug thru passive diffusion via Fick's 1st law of diffusion

• high conc patch diffuse to skin then the low conc bloodstream

• can maintain steady therapeutic lvl

components of a transdermal patch (5)

1. backing film

2. drug reservoir

3. membrane

4. adhesive

5. liner

uses of transdermal patch (5)

1. pain management —> fentanyl patches

2. nicotine replacement therapy —> nicotine patches

3. ischemic heart disease —> glyceryl trinitrate patches

4. hormone replacement therapy —> estrogen patches

5. dementia —> rivastigmine patches

diffusion definition

movement of molecules form a high conc to low conc thru a mem until equilibrium is reached

components of the ficks first law of diffusion

1. diffusion coefficient (D)

2. surface area of mem (A)

3. conc diff (Cd-Cr)

4. thickness of mem (X)

diffusion coefficient D

• how quickly drug move thru mem

• higher D = particles move faster = inc rate of diffusion

how to inc D? (2)

1. permeation enhancer to inc skin permeability

2. physical method to inc skin permeability (microneedle)

surface area of mem A

• where drug interacts and moves thru

• bigger A = more particle move thru = inc rate of diffusion

how to inc A (1)

inc patch size

conc diff (Cd-Cr)

• Cd is conc of donor compartment (higher conc)

• Cr is conc of recipient compartment (lower conc)

• higher Cd-Cr = inc rate of diffusion

how to inc Cd-Cr

use high conc of drugs —> which keeps the drug in a saturated state for controlled relase

thickness X

inc thickness = more effort for diffusion = red rate of diffusion

how to dec X

select area with thinner skin (upper chest, lower abdomen, inner arm)

biological factors affecting transdermal drug delivery (3)

1. skin condition

2. skin age

3. body region skin sites

physiochemical properties affecting transdermal drug delivery (2)

1. skin hydration

2. molecular size & shape

advantage of transdermal therapeutic system (4)

1. non invasive = painless drug delivery

2. improved compliance = reduce dosing freq & tablet burden

3. controlled release = improve therapeutic outcome and red side effects

4. no 1st pass liver metabolism = inc drug conc

disadvantage of transdermal therapeutic system (2)

1. skin irritation/ allergy = adhesive, irritation happen when patch left for prolonged periods of time on the same site

2. cost = more expensive than traditional oral meds