Patches Flashcards
What are patches designed to do?
Deliver drugs across the skin
What are the 2 routes of administration?
Transdermal (systemic)
Transcutaneous (local)
How does transdermal work?
Skin permeation
How does transcutaneous work?
Skin penetration
Where do you put transdermal?
Upper body/arm
Where do you put transcutaneous?
Painful joint/region
What is an example of a transdermal patch?
Fentanyl
What is an example of transcutaneous patch?
Diclofenac
What are the advantages of patches?
Avoids 1st pass
Non-invasive
Extended release
Readily applied + removable
What are the disadvantages of patches?
Low deliverable doses
Skin irritation
Variable absorption
What’s in a patch?
Release liner
Adhesive
Backing layer
What is a release liner?
Protects adhesive, prevents unwanted drug release + contamination
What is an adhesive?
Sticks to skin
What is a backing layer?
Protects formulation
What are the 3 patch designs?
Drug in adhesive
Drug in reservoir
Drug in matrix
What is in a reservoir patch?
Durogesic
Backing layer
Drug reservoir
Rate controller
Adhesive layer
Release liner
What is the function of the polyacrylates excipients?
Adhesive
What is the function of the polyester/ethylene acetate copolymer film excipients?
Backing layer
What is the function of the siliconized polyester excipients?
Removable release liner
What is the function of the dipropylene glycol excipients?
Drug matrix
What is the function of the hydroxypropyl cellulose excipients?
Drug matrix
What is the function of the dimeticone excipients?
Adhesive/drug matrix
What is the function of the EVA excipients?
Rate controlling membrane
What is the function of the PET excipients?
Backing layer
Describe the structure of skin
TOP
Stratum corneum + viable epidermis = epidermis
Dermis (richly vascularised)
Hypodermis
BOTTOM
Describe the stratum corneum
Primary skin barrier
Outermost epidermal layer
Corneocytes
Extracellular lipid matrix
Because the stratum corneum is the main skin barrier, what does this mean?
Rate-limiting
Drug must cross this to be absorbed
What criteria of drugs are best absorbed?
<500 Da
LogP 1-4
Several mg/day = quite potent
What is drug release rate proportional to?
Patch size
= larger the patch
= more drug released per unit time
= greater strength/dose
What are the different diffusion mechanisms?
Transcellular = through the cells (lipophilic route)
Paracellular = around the cells
What does the Franz diffusion cell assess?
Transdermal drug absorption in vitro
How does the Franz diffusion cell work?
Skin is sandwiched between donor chamber + receptor chamber
If drug is found in receptor fluid
= WORKS
How do you increase dermal drug absorption?
Increase dermal drug flux
Modulate Kp
