Pharmacology Flashcards
Vehicle
The way in which a drug is delivered/administered
Choice of specific vehicle is determined by
- physiochemical properties of drug (hydrophobic/hydrophilic)
- the clinical condition
Drug administration through the skin
Topical
Subcutaneous
Transdermal
Topical
Mainly for local effect but also used to treat underlying tissues
Direct application to the skin
Most important barrier to drug penetration
Keratin layer (stratum corneum) - very hydrophobic
Keratin layer drug penetration
Bricks are corneocytes
Mortar is the multiple intracellular lipids
INTRACELLULAR ROUTE
- most common, highly torturous, move around the bricks
TRANSCELLULAR ROUTE
- drug diffuses into bricks and enters underlying bricks
Topical drug uses
Local effects in the treatment of
- superficial skin disorders
- skin infections
- itching
- dry skin
- warts
Topical drug vehicles (6)
Ointments Creams Gels Lotions Pastes Powders
Factors influencing the absorption of topically applied drugs: Vehicle
Influences rate and extent of absorption of a topically applied drug
Lipophilic drug in lipophilic base
Because vehicle is highly lipophilic, it will tend to retain the lipophilic drug so there will be limited diffusion of drug across the keratin layer
Lipophilic drug in hydrophilic base
Ideal combination for moving a lipophilic drug across the keratin layer. Will achieve optimum concentration of drug in the skin
Hydrophilic drug in lipophilic base
Lipophilic base pushes drug into skin but it will be difficult for drug to diffuse around the hydrophilic environment
Factors influencing the absorption of topically applied drugs: drug conc
Only the soluble fraction provides the driving force of absorption
Factors influencing the absorption of topically applied drugs: partition coefficient
Only a small fraction partitions into the keratin layer - so poor absorption.
Increased partitioning results from decreased barrier function of the keratin layer.
To improve hydration we need to:
- hydrate the skin by occlusion (prevention of water loss)
- inclusion of excipients which increase solubility
Factors influencing the absorption of topically applied drugs: Nature of the skin
Site of application is important as the thickness of the keratin layer varies at different body parts
For areas of thicker skin, use a high potency glucocorticoid
If skin is broken then movement of the drug across it will be faster
Factors influencing the absorption of topically applied drugs: drug preparation
Consider what the drug salt is (butyrate stronger vs acetate weaker)
Consider the vehicle in which the drug is administered
Subcutaneous route of administration
Delivered by a needle into the adipose tissue just beneath the surface of the skin
