Routes of Administration: Topical Preparations Flashcards
1
Q
Describe topical drug delivery.
A
- Administered on tissue surface.
- Treatment of a local condition.
- Site of administration is site of therapeutic action.
- Minimise systemic absorption to minimise side effects.
- Commonly skin (cutaneous/transcutaneous), but could refer to other tissue.
2
Q
What is an ointment?
A
Drug dissolved or dispersed in a greasy base
3
Q
Describe the features of ointments.
A
- Occlusive: promotes skin hydration by minimising trans epidermal water loss
- Can be difficult to spread
- patient acceptability could be low
4
Q
What is a cream?
A
- Semi-solid emulsion
- Multiphase dispersion of oil in water or water in oil
5
Q
What are the advantages of creams?
A
- Longer residence time than lotion
- Mixable with skin secretions , easily washable
- Excellent patient acceptability
6
Q
What is a gel?
A
- Semi-solid or viscous liquid, often clear or transparent
- Polymer network interpenetrated by a liquid
- Mostly aqueous: hydrogels or hydro-alcoholic gels
- Drug dissolved or dispersed in liquid component
- May form occlusive film on skin when dried
7
Q
What is a lotion?
A
- Typically water-based, thus non-occlusive:
- Solution, suspension or emulsion.
- Primarily used for cleansing or disinfection.
- High spreadability: ideal for covering large area thinly.
- Suitable for administration on hairy skin.
- Short residence time: increasing viscosity prolongs
residence time.
8
Q
What is a foam?
A
- Dispersion of gas within a liquid.
- Drug dissolved or dispersed in liquid phase.
- Available as pressurised cans.
- Foam generated during use and stable only momentarily.
9
Q
Describe a spray.
A
- Aerosol: Dispersion of liquid droplets in gas.
- Fine mist generated using propellant in pressurised can.
- Administration without direct skin contact.
- Rapid and even coverage of large surface area.
10
Q
Describe a patch.
A
- Similar to transdermal patch but for topical delivery.
- Solid dosage form containing drug on an adhesive film.
- Discrete dosage unit enables accurate dosing.
- Provides occlusion, dose retention, and protection of formulation from environmental
contamination during use.
11
Q
What are the advantages of topical preparations?
A
- Avoid gastrointestinal drug degradation and hepatic first-pass metabolism.
- Non-invasive, thus well accepted by patients.
- Better drug targeting, thus minimal systemic side effects.
- Easy dose withdrawal in case of adverse reactions.
- Convenient: portable and self-administrable.
12
Q
What are the disadvantages of topical preparations?
A
- Low skin permeability: only a small selection of drugs deliverable, and even then
their uptake is slow. - Skin irritation.
- Difficult to determine dose accurately (e.g., creams, gels, ointments).
13
Q
Name the cellular layers of the human skin.
A
- Epidermis
- Dermis
- Hypodermis
14
Q
Describe the stratum conreum of the epidermis.
A
- Dead cells with a hard protein envelope: the cells contain keratin and are surrounded by lipids
- It is the permeability barrier
15
Q
Describe dermal drug transport mechanisms.
A
- Partitioning: from one medium to another, solubility-driven
- Diffusion: within the same medium down conc. gradient
16
Q
What is skin permeability?
A
A function of the partitioning coefficient and the diffusion coefficient.
Kp = KD/h
Kp = permeability co efficient
K = partition coefficient
D = Diffusion coefficient
h = Diffusion path length
17
Q
Why are transcellular and paracellular pathways important?
A
- For traditional dosage forms
- Transcellular route (hydrophilic drugs)
- Paracellular route (lipophilic drugs)
18
Q
What is the shunt pathway?
A
- Through hair follicles and sebaceous glands
19
Q
State the factors affecting dermal drug transport.
A
- Drug properties: lipophilicity, molecular weight
- Anatomical site: barrier thickness, hair follicle density
- Age: thickness, hydration, lipid content and microvascular clearance decline with age, corneocytes enlarge with age
- Disease: broken skin = higher permeability, scaly skin = impaired permeability barrier and dehydrated = reduced permeability
- Thickened skin = reduced permeability due to increased diffusional path length
20
Q
What is tape stripping?
A
- Stratum corneum progressively removed by adhesive tape.
- Drug assayed relative to protein content of the strip.
- Assumes each tape removes materials from single cellular layer.
- Tape constituents may contaminate sample.
21
Q
Descibe human skin for in vitro skin models.
A
- Closest to in vivo human skin.
- From cadavers or post-operative sources.
- Requires informed consent and ethical approval.
22
Q
Describe animal skin for in vitro skin models.
A
- Pig skin closest to human skin anatomically and kinetically.
- Murine skin cheap and easy to source.
- Hairless skin models minimise drug transport through follicular pathway.
- Ethical and legal considerations
23
Q
Descibe artificial membranes for in vitro membranes.
A
- Alternatives to native biological tissue.
- Bio-engineered skin equivalents with cellular components, e.g. Episkin™
- Non-biological polymeric membranes, e.g. Strat-M®
- Validated through correlation studies using a variety of drugs spanning a range
of structure, therapeutic classes and physicochemical properties. - Cheap, safe, ethical and highly reproducible.
