Dermatopharmacology Flashcards
What 5 things does the skin protect the body from?
- temperature fluctuations
- allergens
- pollutants
- toxic chemicals
- bacteria, fungi, parasites, viruses
Where is skin the thickest? Thinner? Thinnest?
THICKEST: over head; dorsum of the neck, back, and sacrum; plantar and palmar surfaces of the feet
THINNER: ventral abdomen; medial surface of the limbs; inner pinnae
THINNEST: over the scrotum
What are the 2 primary cell types in the epidermis? What are the 5 layers?
keratinocyte origin and nonkeratinocyte origin
- stratum corneum - primary barrier to percutaneous drug absorption
- stratum lucidum
- stratum granulosum
- stratum spinosum
- stratum basale - constantly dividing
What happens when drugs are able to pass through the stratum corneum?
subjected to drug-metabolizing enzymes similar to those in the liver
- oxidation
- reduction
- hydrolysis
- conjugation
What part of the epidermis acts as the primary barrier to prevent loss of water, electrolytes, and macromolecules and excludes external agents? Why?
stratum corneum
- abundance of keratin
- configuration and content of intercellular lipids
What are the 3 routes of absorption of topically applied drugs to the skin? How do they move through the stratum corneum?
- stratum corneum - between cells, not through
- hair follicles
- sweat or sebaceous glands (that open into hair follicles)
passive diffusion
What is the structure of the stratum corneum like?
“brick and mortar”
brick = stratum corneocytes
mortar = intercellular lipids where drugs penetrate
What kind of drugs move best through intact skin? More of the drug is able to pass through the skin of what kind of animal?
lipophilic > polar
heavily haired - larger number of hair follicles
What 2 things must occur before a drug can be delivered to the epidermis under the stratum corneum?
- drug must move out of the vehicle and onto the surface of the stratum corneum
- drug must be able to penetrate the stratum corneum
What is a vehicle? What affects its movement through the skin?
substance in which a medicinally active agent is topically administered, usually inactive (but can be therapeutic)
physical and chemical properties
Which pH of drugs allows them to move best across the stratum corneum?
nonionized moiety of a weak acid or base - pH/pKa from 4.2 to 7.3
What are the optimal vehicles?
those in which the drug is soluble enough to enter into solution, but it not too soluble that it will persist in the vehicle and slow down the release of the drug into the skin
What 4 other factors affect percutaneous absorption?
- MW of the chemical
- temperature of the air
- blood flow
- skin age
What are 2 types of antiseborrheics?
- KERATOLYTICS: hydrate and soften stratum corneum to promote mechanical removal
- KERATOPLASTICS: normalize keratinization by slowing basal cell proliferation
How are salicylic acid and sulfur used as antiseborrheics?
SALICYLIC ACID: keratinolytic and keratoplastic with mild antibacterial, antifungal, and antipruritic actions
SULFUR: keratinolytic and keratoplastic with mild follicular flushing action and antibacterial/antipruritic effects
How are coal tar and benzoyl peroxide used as antiseborrheics?
COAL TAR: keratinolytic and keratinoplastic with degreasing action and commonly used with salicylic acid and sulfur
BENZYOL PEROXIDE: keratinolytic with bactericidal, degreasing, and follicular flushing activity, and is a strong oxidizer that generates free radicals
In what patients is coal tar avoided in?
feline - frequent irritant, commercial shampoos can be used
When is it indicated to use benzoyl peroxide?
treatment of keratosis and pyoderma
How are resorcinol and selenium sulfide used as antiseborrheics?
RESORCINOL: keratinolytic with bactericidal and fungicidal properties that promotes hydration of keratin (typically combines with other keratinolytics, sulfur, salicylic acid)
SELENIUM: keratinolytic and keratoplastic that slows down cell proliferation and sebum formation
- muscous membrane irritation may result in accidental contact
What do antipruritics do? What are the 4 mechanisms?
provide temporary relief from itching
- substitutes itching sensation
- protects the skin
- anesthetizes peripheral sensory nerves
- biochemical agents given topically
How do antipruritics substitute itching sensations? How can they protect the skin?
substitute with another sensation, like heat or cold: menthol, camphor, warm soaks/baths, ice packs
protect from external factors, like scratching, burning, irritants, and changes in humidity/temperature: bandages, impermeable agents
What antipruritics are used to anesthetize peripheral sensory nerves? What biochemical agents are given topically to treat pruritis?
local anesthetics: benzocaine, lidocaine, pramoxine (Dermacool) - can cause allergic sensitization
glucocorticoids
What type of glucocorticoids provides greater efficacy? How do they cause systemic effects? When does this happen more commonly?
ointment (still not as potent as oral or injectables)
absorbed through the skin - potent fluorinated agents (betamethasone, dexamethasone, triamcinolone, flumesthasone, fluocinolone)
Which glucocorticoid has been formulated to the applied to the entire body?
Triamcinolone (0.015% Genesis spray) - good for spot treatment of pruritis