Topical Drug Delivery And to the ear Flashcards
What are the advantages of topical drug delivery?
Easy and painless High patient compliance Avoid first past metabolism Increased efficacy Less side effects
What are the limitations of topical drug delivery?
Frequent allergies/ irritations
Few drug work this way
Enzymes on skin cause metabolism
Low drug penetration into skin
What is the basic structure of the skin?
Stratum corneum Viable epidermis Dermis Subcutaneous fat Underlying tissue
What is the basic functions of the skin?
Effective barrier to chemicals and microorganism
Control body hydration and temp
Protection against UV
Mechanical barrier
What is the structure of the stratum corneum?
10-15 layers of corneocytes
Tightly compacted cell layers which are polygonal, elongated and flat
Cells exclusively contain keratin
Embedded in Lipid bilayers
What are the three ways drugs can penetrate the stratum corneum?
Tansappendageal
Transcellular
Intercellular
What are the biological factors that can affect drug permeability?
Skin hydration
Age
Body site
Pathological disorders
How do the following drug properties effect drug permeation: MW, partition coefficient, pKa, concentration in vehicle?
MW - poor penetration if > 500 daltons
LogP > 3 might accumulate in s. Corneum
pKa- drug must be neutral at the pH of the skin
Conc in vehicle - diffusion into skin depends on conc gradient
How do pro drugs work topically?
Usually esters are cleaved by esterases in the skin to release parent molecule
What are the 2 liquid formulations and 3 semi solid formulations of topical drugs?
Liquid - solutions, emulsions
Semi solid - ointments, creams and gels
What vehicle properties effect drug permeation and how?
Occlusion - ointments and w/o cream prevents water evaporation from skin
Permeation enhancers used - decrease barrier properties of s. Corneum
How can permeation enhancers work?
Modify keratin conformation leads to swelling increased hydration
Disruption of lipid bilayers leads to increased permeability
Alter solvent properties of s. Corneum which increases partitioning
What diseases of problems can cause the administering of drugs to the ear?
Bacterial infection
Eczema
Excess earwax
What are the key points of the external ear?
Covered by skin
Earwax produced by glands in ear canal
Earwax repels water
How can drugs be administered to the ear?
External - ear drops, creams,
Ointments
Middle ear - systemic delivery or injection through eardrum
Inner ear - high doses
Of systemic delivery
Delivery through the middle ear
