Dermatologic Pharmacology Flashcards
What is the primary barrier to absorption of substances through the skin (the rate-limiting step)? Why is anything ever absorbed?
Passage through the stratum corneum. Passive diffusion via a concentration gradient.
Is drug absorption increased/decreased with hydration? What about with injured/diseased/ulcerated skin (eczema, psoriasis)? What about with retained keratin (icthyosis)?
Increased with hydration and injury/disease/ulcers that opens skin. Decreased with retained keratin.
Regional differences in penetration?
Mucous membranes, scrotum, eyelids, face, chest/back, upper arms/legs, lower arms/legs, dorsa of hands/feet, palmar/plantar surfaces, nails.
3 important drug variables that increase absorption?
High concentration (more important than volume), lipophilicity, small molecular size
Strongest versus weakest vehicle? Should vehicles be irritants?
Ointment versus solution, based on lipid content. Irritants alter skin barrier and increase absorption.
4 important innate skin variables that increase absorption?
Thin stratum corneum, increased cutaneous vasculature, increased SA, mucosal surface
What is an ointment? Hydrating or not? Potency?
“Water in oil emulsion” “Hydrating” “Strong potency”
What is a cream? Hydrating or not? Potency?
“Oil in water emulsion” “Some hydration” “Moderate potency”
What is a gel? Hydrating or not? Potency?
“Semisolid emulsion in alcohol base” “Drying” “Strong potency”
What is a lotion/solution? Hydrating or not? Potency?
“Powder in water (some with oil) “Drying (variable)” “Low potency”
What do powders do with moisture and friction? How do they adhere to the skin?
Absorb moisture, Reduce friction, Adhere poorly and clump.
Are oils (greases) protective? Are ointments?
Greases are protective, Ointments are occlusive
With Candida in a body fold, what should treatment be?
Cream (hydrate) then powder (prevent recurrence)
When are pastes useful?
Ulcers, Chronic dermatoses
When are gels useful?
Hairy areas – They allow for greater penetration than lotions
What is a gel?
Liquid converted to a semisolid by addition of a polymer (“liquid in a mesh”)
What is a paste?
“A smooth viscous mixture that has adherence-like properties”
Where are solutions most useful for?
Scalp – They penetrate through hair and leave no residue
AKA oil-in-water? Is this hydrating?
Vanishing cream; DRYING (water evaporates)
AKA water-in-oil? Is this hydrating?
Oily cream; some hydration
What is an aerosol?
“Solid/liquid suspended in a gas”
What is a foam?
“A substance formed by trapping pockets of gas in a solid/liquid”
How many classes exist for glucocorticoids? How are they ranked?
Seven classes: Class 1 (“Super-Potent’”) to Class 7 (“Mild”)
Glucocorticoid (steroid) side effects?
Atrophy/thinning of skin/collagen (“steroid atrophy”), stretch marks, telangiectasias, acne, purpura, pigmentary changes, growth of bacteria, cataract or glaucoma if applied near eye with long term use; Systemmicaly affects the hypothalamic-pituitary-adrenal axis and can cause growth retardation (especially in children, because they will absorb better with an increased SA:V ratio)
UVA & UVB light therapy mxn?
UV therapy alters the immune response in the skin: Immunosuppression of T-cells via type I or type II reactions: mono- or bifunctional adducts in DNA
UV light therapy for?
Inflammatory conditions: psoriasis, atopic dermatitis, CTCL, lichen planus (NOT useful for non-inflammatory conditions)
UV light therapy side effects?
Skin cancer, thinning/leathering of the skin
UV light therapy used with?
Psoralens (photosensitizing agents that increase efficacy)
What agents besides psoralens sensitize skin to light therapy?
Phenothiazines, thiazides, sulfonamides, NSAIDs, tetracycline, benzodiazepenes
Psoralens belong to what class of compounds?
Furocoumarin
