Percutaneous absorption Flashcards
what is percutaneous absorption
absorption through the skin
what is the rate limiting step of percutaneous absorption
diffusion through the stratum corneum because it is highly keratinized
what are the routes of percutaneous absorption
across the stratum corneum
via appendages
what is the brick and mortar model of the stratum corneum
intercellular: using the lipid bilayer (aka mortar)
intracellular: using the cells (aka bricks)
what is the paritition coefficient (P)
Ratio of concentration of drug in the SC to concentration of drug in the vehicle
do you want a large P value or a low one
Larger the partition coefficient the more affinity the drug has for the skin
Want a drug with a high affinity for the stratum corneum
Want more hydrophobic drugs because they will got through the stratum corneum more readily than hydrophilic drugs
Select the drug coming as an acid or a base and not a salt as those will be more lipophilic
are vehicle factors important in percutaneous absorption
YES: drug is released differently from different vehicle types
what are vehicle factors that affect drug delivery
pH–>determines ionization of the drug (Non-ionized penetrates better)
Co-solvents–>concentrate drug on skin
Release of drug from vehicle–>optimize with the appropriate vehicle
Penetration enhancers–>temporarily increase permeability of the skin
does diseased skin affect percutaneous absorption
for the most part increases absorption because the barrier is compromised
what other skin factors play a role in percutaneous absorption
age of the skin
thickness of the stratum corneum
skin metabolism
circulation to the skin
why does C1 initially increase when looking at Fick’s law
Drug accumulates on the surface: means C1 increases initially
If it doesn’t accumulate absorption will be slow
what treatments target the skin surface
Camouflage or cosmetic preparations
Protective films–>barriers, sunscreens
Antifungal and antibacterial preparations
what treatments target the stratum corneum
Emollients and moisturizers (increase water content)
Keratolytic (to remove dead cells)
what treatments target the epidermis and dermis
Majority of dermatological agents target this area
Topical steroidal and non-steroidal anti-inflammatory agents
Local anesthetic agents
Antihistamines/anti-pruritic
Anticancer drugs
what treatments target the systemic circulation via percutaneous absorption
hormone replacement therapy
others that have since become patches (nitro for angina, scopolamine for motion sickness)
what treatments target skin appendages
Antiperspirants (sweat glands)–>aluminum salts
Exfoliants (acne)–>salicylic acid, tretinoin, benzoyl peroxide
Depilatories–>thioglycolates
Antibiotics–>clindamycin, erythromycin, tetracycline
Antifungals–>clotrimazole, miconazole
what is the use of powders
Adhere little to skin
Primarily for hygienic purposes
what is the use of liquids
Used as wet dressings
Oozing dermatoses
Chapped skin
what is the use of ointments
Emollient, occlusive effect
Avoid in oozing conditions (cant absorb extra water) and acne
what are shake lotions used for
Cooling and drying effect
Effective for: erythematous and papular dermatoses, vascular dermatoses, inflamed, irritated insect bites, hives
what are pastes used for
Drying and absorbing effect
Effective for oozing, lichenified and keratotic conditions
what are creams used for
Cooling, non-occlusive effect
Good moisturizers and emulsifiers (can take up liquids)
Non-greasy
types of bases used in acne
liquids (water or alcohol based)
gels
creams, o/w emulsions
NOT occlusive
types of bases used in dermatitis
absorption bases with oozing
Emulsions: because they have a moisturizing effect as well and can contain humectants
Better to use w/o emulsion to create a protective barrier
Creams, lotions, ointments
types of bases used in psoriasis
occlusive (the more the better): hydrocarbons, silicone bases
creams
ointments with plastic wrap to increase hydration
types of bases used in herpes simplex
protectant
cream
types of bases used for corns and calluses
occlusive: the more the better (easier to remove the abrasion)
bases used for tinea pedis
non-occlusive
o/w creams
bases used for tinea capitits
non-occlusive
gels
creams
what are topical steroids used for
relief of inflammation and itchiness
what does fluorination of C9 on a corticosteroid do?
increases inflammatory activity
what does addition to C17 or C21 on a corticosteroid result in?
influence solubility (more lipophilic substituent increases skin penetration)
what does addition of alpha-alkoxycarbonyl to the C16 of a corticosteroid result in
antedrug and decreased systemic side effects
how many classes of corticosteroids are there (name them)
7 Super/ultra potent (1) High (2 and 3) Intermediate (4 and 5) Low (6 and 7)
how is potency of a corticosteroid determined
blanching assay
Corticosteroids vasoconstrict blood vessels on the surface of the skin causing it to change colours
