P15: Ocular Drug Delivery Flashcards
what are ocular dosage forms used to treat
belpharis, conjunctivitis, keratitis, trachoma, dry eye
intraocular disorders like glaucoma
what is the anatomy of the eye
cornea, pupil, iris, sclera, conjunctiva, aqueous humour, lens, vitreous homour, choroid, retina
what are the advantages of ocular dosage forms
drug delivery directly to the site of action, drug available at higher concentration than via oral administration, local application minimises side effects, self-administrations is easy
what are the disadvantages of ocular dosage forms
drug retention on eye surface is poor, rapid clearance, low tear volume so loss of dose, frequent dosing required, inconvenience resulting in poor patient compliance, sterile manufacture of dosage forms is essential, local side-effects, ointments can cause blurring of vision
where is the conjunctiva
located at the side of the eye and joins on to cornea and eyelids
what is the conjunctiva made from
non-keratinised, stratified squamous epithelium with goblet cells and also stratified columnar epithelium
highly vascularised with many microvessels
what does the conjunctiva do
produces and maintains tear film
greater permeability than cornea
what three layers is the cornea composed of
multi-layered lipid rich epithelium
central aqueous matrix called stroma
endothelium, single-celled and lipid rich
what does the cornea do
controls drug diffusion to inner eye
efficient permeation through lipoidal epithelium/endothelium and through aqueous stroma required drugs with oil and water solubility
cornea is avascular and negatively charged
what is lacrimal fluid
secreted from lacrimal glands into surface of eye
what is the pH of lacrimal fluid
7.4
good buffering capacity that neutralises unbuffered solutions effectively
beffering from carbonic acid, other weak acids and protein
what is corneal absorption
major route for ocular drug absorption, transcellular lipophilic and paracellular hydrophilic pathways, little evidence of active transport mechanisms, lipophilic-hydrophilic-lipophilic structure of cornea means that drug should have a degree of water and lipid solubility
what is conjunctival absorption
drug passes through conjunctiva and sclera, sclera is fibrous membrane mainly connective tissue to allow permeation of large hydrophilic compounds with poor corneal absorption, most drug is lost into local capillary bed and enters systemic circulation, transporters are present
when are suspensions preferred
when drug has chemical stability problems, used when potency of lipophilic drug is greater than that of its salts
how are drug salts chosen
solubility to ensure high concentration/driving force for absorption
what are the physical properties of aqueous ocular dosage forms
low molecular weight, water and oil solubility, balanced log P
how does drug absorption occur across the cornea
essential in treatment of glaucoma, weakly acidic and basic drugs in use, lipid-aqueous-lipid nature of cornea structure
what vehicle is used in aqueous ocular dosage forms
purified water USP
how are viscosity modifying agents used in ocular dosage forms
hydrophilic polymers control flow rate of drops from dispenser to increase residence times of formulation
they must be filtered during manufacture, easily sterilised by filtration and compatible with other excipients
what is polyacrylic acid used for
cross-linked form in aqueous gels to treat dry eye syndrome
what are some examples of preservatives used in ocular formulations
benzalkonium chloride, parabens, organic alcohols, antioxidants
what is intraocular drug delivery
intravitreal drug injection has become a popular method of treatment of many retinal diseases, including age-related macular degeneration, diabetic retinopathy and retinal vein occlusions
significant increase in frequent of intravitreal injections since introduction of anti-VEGF medications
