Pharmacology and the Skin Flashcards
What are the major routes of drug administration regarding skin?
Topical - local effect
Transdermal - systemic
Subcutaneous - systemic
What is the most important barrier a drug must penetrate in the skin?
Stratum corneum (keratin layer)
Through which route do drugs pass through the stratum corneum -
transcellularly or intercellularly?
Intercellularlly
Give examples of when the topical route of administration may be used
Psoriasis Eczema Skin infection Itching Dry skin Warts
Give examples of some vehicles that may be used for topical administration
Ointments Creams Gels Lotions Pastes Powders
With regard to water and fat solubility, what is the most effective combination of drug and vehicle for the drug to enter the blood system? Explain why.
A lipophilic drug in a hydrophilic vehicle
Drug easily crosses the lipophilic stratum corneum and is not kept by vehicle
Excipents increase/decrease solubility and increase/decrease absorption of drugs.
Increase and increase
Why does a fatty substance being applied to the skin help drug absorption?
As it reduces water loss from the skin and makes the stratum corneum more permeable to drugs
Why should, when prescribing a topically-applied drug, the drug salt be stated specifically?
As the salt can affect the potency of the drug itself
What factors should be considered when prescribing a glucocorticoid for topical use?
Body site (thickness of stratum corneum) State of skin Occlusion Vehicle (cream, powder etc.) Concentration Drug salt
Give some side effects of long term use from higher potency steroids?
Steroid rebound
Skin atrophy
Systemic effects
Infection spread
Describe (simply) the molecular mechanism of glucocorticoids
Glucocorticoids enter cells by diffusion where they combine with GR-alpha.
They then translocate to the nucleus where they bind to GRE in the promotor region of specific genes.
They will then either switch on or off the translocation of these genes to alter mRNA levels and the rate of synthesis of mediator proteins
Give some advantages of using the subcutaneous route of administration
Slow absorption
Can administrate oil-based drugs
Simple and painless
Does administering a drug through the skin avoid first pass metabolism?
Yes
Explain how transdermal drug delivery works
Drug is incorporated into an adhesive patch applied to epidermis which diffuses across cutaneous barrier
