Routes of Administration (Topical) Flashcards
What are the different ways a drug can be delivered topically?
- Topical
- Administered at tissue surface (site of therapeutic action) for local condition
- Minimise systemic effects
- Transdermal
- Administered at tissue surface act at a remote site (systemic)
- Percutaneous: Through skin
Name some formulations for topical use?
- Ointment
- Creams
- Gel
- Lotion
- Foam
- Spray
- Patch
What is an ointment?
- Drug dissolved in greasy base
- Promotes hydration by minimising transepidermal water loss
- Difficult to spread, patient acceptability low
What is a cream?
- Semi solid emulsion (commonly oil and water)
- Oily creams (W/O) w= continuous, O = oil added to water is less greasy than ointments
- Excellent patient acceptability
What is a gel?
- Semi solid or viscous liquid : often clear or transparent
- Drug dissolved or dispersed in liquid component
- May form a film on skin when dried
What is a lotion?
- Typically water based and non-occlusive (doesn’t seal off skin)
- Solution, suspension or emulsion
- High spreadability (on hair skin)
- Short residence time
What is a foam?
- Dispersion of gas within a liquid phase
- Available as pressurised cans, foam generated during use is stable momentarily
What is a spray?
- Aerosol: dispersion of liquid droplets in gas
- Fine mist generated. Administered without direct skin contact. Even coverage with large SA
What is a patch/
- Similar to transdermal but for topical delivery
- Drug on adhesive film
- Provides dose retention and protection of formulation from environmental contamination
What are the advantages of topical delivery?
- Avoids GI drug degradation and hepatic first pass metabolism
- Non-invasive
- Better drug targeting and minimal side effects
- Easy dose withdrawal (side effects)
- Convenient/ portable
What are the disadvantages of topical delivery?
- Low skin permeability (skin tries to keep chemicals out) and uptake = slow
- Skin irritation
- Hard to determine dose accurately
What are the cellular layers of the skin?
- Epidermis
- Dermis
- Hypodermis
What is the epidermis?
- Stratum corneum : dead cells with a protein envelope
- Permeability barrier.
- Corneocytes (bricks) = hydrophilic
- Extracellular lipid matrix (mortar) = lipophilic
What are the dermal drug transport mechanisms?
- Partitioning: from 1 medium into another, solubility driven
- Diffusion: within the same medium, down concentration gradient
What are transcellular and paracellular pathways for topical dosage forms?
- Transcellular: Straight through cells. One end to another (hydrophilic drugs)
- Paracellular: Around corneocytes (lipophilic drugs). Corneocytes have hydrophilic centres
What is the shunt pathway?
- Through hair follicles and sebaceous glands
- Traditionally regarded as negligible due to small skin area
What are factors affecting dermal drug transport?
- Drug properties: Lipophilicity, molecular weight
- Anatomical site: Barrier thickness, hair follicle density
- Age: thickness of skin, corneocytes enlarge with age
- Disease: Broken skin, thickened skin
What is tape stripping to access topical drug penetration?
- Stratum corneum progressively removed by adhesive tape
- Drug assayed relative to protein content on strip
How do you use the diffusion cell to assess topical drug penetration?
- Skin sandwiched between donor and receptor chambers
- Statum corneum facing towards donor and administered
- Receptor C = filled with receptor buffer
- Only route = from donor to receptor through skin
- Drug sampled from receptor C and assayed
What are the in vivo skin models?
- Human skin
- Animal skin (pig skin)
What are the in vitro skin models?
- Artificial membranes: Bio engineered skin, cheap, ethical
