Pharmacology in the skin Flashcards
What are the major routes for drug adminstration via the skin?
Topical
Transdermal
Subcutaenous
What are the advantages of topical drug administration?
Used for local, achieves a high drug concentration at the intended site of action minimising the adverse affects which might occur through systemic absoprtion of the drug
What is the most important layer of skin in regards to pharmacology?
Stratum corneum - important barrier to drug penetration into the skin or across it
What makes up the stratum corneum?
Corneocytes, intracellular lipids
Where do drugs go when they move thorugh the trancellular route?
Corneocytes - aggregated keratin filaments embedded in a filaggrin matrix surrounded by a cornified cell envelope
Where do drugs move when they go thorugh the intercellular route?
Lamellar structures of intercellular lipids (cholesterol, free fatty aicds)
Highly hydrophobic, acts as a resovoir for lipid-soluble drugs such as topical corticosteroids
What are the chemical properties of an ointment?
Very highly hydrophobic
What are the chemical properties of lotions and pastes?
Highly hydrophilic
When are topical treatments used in dermatology?
Treatment of superficial skin disroders such as psoriasis, eczema Skin infections Itching Dry skin Warts
What is used to treat superficial skin disorders?
Glucocorticoids
Retinoids
What is used to treat skin infections?
Antivirals
Antibacterials
Antifungals
Anti-parasitics
What is used to treat pruritus?
Antihistamines
What is used to treat dry skin?
Moisturising agents
What is used to treat warts?
Keratolytic agents
What are the different types of vehicles?
Ointments Creams Gels Lotions Pastes Powders
What dictates the type of vehicle?
Physiochemical properties of the drug
Clinical condition
What factors infleunce the absoprtion of topically applied drugs?
Permeability coefficient
Concentration of drug in the vehicle
What will determine the permeability coefficient?
Properties of the drug
Properties of the barrier `
What are important factors in how the vehicle affects the rate and extent of absorption of a topically applied drug?
Dissolved conc of drug in vehicle
Maximising movement of drug from vehicle into the strateum corneum
What are the basic rules of coefficient partitioning?
A lipophilic drug in a lipophilic base is soluble in vehicle and the skin and partitions between the two
Lipophilic drug in hydrophobic base is more solube in skin so will partition readily
Hydrophilic drug in hydrophobic base will partiton to a limited extent
A hiydrophilic drug in a hydrophilic vehicle will remain on the surface of the skin
What is the function of excipients?
Enhances solubility and enhances absorption
What is an example of an excipient and its related drug?
Propylene glycol in hydrophobic glucorticoids
Why do transdermal patches provide a constant rate of delivery of drug?
As the dissolved frug is removed into the skin, the conc on the patch decreases and therefore the undissolved drug will dissolve creating a stady stream of drug
What factors can improve partitioning?
Hydration of the skin by occulsion
Inclusion of excipients which also increase solubility of hydrophobic drugs
What factors will influence the absorption of topically applied drugs?
Nature of the skin - site of application, hydration of skin, integrity of the epidermis
Drug preperation - drug concentration, drug salt, the vehicle
What are the effects of glucocorticosteroids?
Anti-inflammatory
Immunosuppressant
Vasoconstricting effects
Anti-proliferating action upon keratinocytes and fibroblasts
What will glucocorticosteroid penetration, potency and clinical effect vary with?
Body site State of skin Occlusion Vehicle Conc of drug Form of drug
What are the side effects of long term use of high potency steroids?
Steroid rebound Systemic effects Spread of infection Steroid rosacea Production of stretch marks
What receptor do glucorticosteroids signal via?
Nucleur receptors class 1
