LEC6 - Skin Penetration & Drug Delivery Flashcards
State the rate determining barrier in permeation and describe its features
Stratum Corneum - densely packed, keratinised cells consisting of 75-80% of lipophilic materials
Identify the 3 permeation pathways
Transcellular - across cells
Intercellular (paracellular) - between cells
Transappendageal - through hair follicles, sweat glands and sebum glands
Explain passive diffusion
Movement of the drug into the deeper layers of the skin following random molecular motion.
Transfer rate proportional to concentration gradient.
Explain the difference between topical and transdermal absorption
Transdermal - designed for drug delivery past the skin to reach circulation and exert systemic effects
Topical - designed to deliver drugs into the skin to treat skin disorders (epidermal or dermal disorders)
State the 3 types of factors that affect drug permeation
- Physicochemical
- Biological
- Formulation
Suggest 3 different strategies to enhance topical delivery
- Removal of stratum corneum
- Penetration enhancers
- Advanced dosage forms
Discuss the advantages of topical formulations
- Avoids first-pass metabolism
- Easy application
- Reduced side effects/avoids fluctuation in drug levels
- Reduce drug dosing (controlled release)
- > Easy to administer/painless
- > Better patient adherence
- Achievement of efficacy with lower total daily dosage of drug by continuous drug input
- Direct tissue targeting/rapid termination
Discuss the disadvantages of topical formulations
- Molecules of drug must not irritate or harm the skin
- Intra- and inter-variability associated with the permeability of intact and diseased human skin
- Metabolism in skin
- Skin irritation and sensitisation
- Technical difficulties in adhesion
- Skin is a strong barrier for drug penetration
Explain chemical enhancers
Substances that can modify the barrier properties of the stratum corneum to enhance drug permeation and absorption through the skin
