Patches summary

Patches
Functions of the skin
- designed to keep xenobiotics (chemical foreign substance) and micro-organisms out
of the body
- contains nerve endings to detect touch, pressure, temperature and pain
- sweat lands to eliminate waste and maintain electrolyte balance
- blood supply
- sweat: thermoregulation
What is the stratum corneum?
Outermost layer of epidermis
Top layer of skin
Dead, flattened skin cells surrounded bu lipids
Serves as a barrier to protect from pathogens, chemicals and UV radiation
Paracellular vs transcellular routes
Transcellular:
- hydrophilic drugs
- penetrates the aqueous regions of keratin filaments
Paracellular:
- most drugs and lipid molecules
- stays in lipid bilayers disrupting lipid regions
- pass between the cells
Topical vs transdermal
 topical: only local, the top layers of the skin
 transdermal: fooling the stratum corneum to allow drugs into the skin
Passive vs active transdermal delivery
Passive:
 diffusion of a drug
 constant diffusion rate
 depends on skin and patch characteristics
Active:
 using a method to aid transfer
 e.g. physical (microneedles)
 or electrically assisted methods (iontophoresis)
Types of passive transdermal patches
Matrix
Reservoir
Drug in adhesive
Advantages of passive transdermal patches
 painless
 non invasive
 controlled blood levels
 termination possible by removing patch easily
 less inconvenience e.g. IV administration
 vomiting/diarrhoea/coma patients unable to take oral medication
 avoidance of the GIT-no 1st pass metabolism, food effects, intestinal degradation, etc
 increased patient compliance