2 - Drugs and the eye Flashcards
topical drugs used by optoms
- dianostic: mydiatics, cyclopegics, anaesthetics
- lubricants, sodium hyaluronate
- anti -infectives, chloramphenicol
- anti- allergy
systemic drugs used by optoms
- anti histamines
- NSAIDS
- eye nutrients
factors influencing drug delivery to eye
- topical drugs
- pre- corneal factors
- corneal penetration
- inside the eye
pre - corneal factors
- single drop exceeds the capacity of the conjunctival sac to contain it has little differene in the efficacy
- tear turnover rate
- higher rates of drainage occur with larger drop sizes with an increased risk of systemic toxicity
- Nasolacrimal drainage (once drug gets into tears) exceeds the amount of drug that penetrates cornea
need to minimise amount of drug that goes down nasolacrimal route as that ^ risk of systemic absorption. this occurs with ^ drop sizes
corneal penetration (cornea is main route of entry for topical medication)
for a drug to pass through cornea, needs a combo of hydrophillic and hydrophobic properties - weak acids and weak bases
once the drug has penetrated the cornea, what happens inside the eye?
- mixes with the aqueous humour. some drug is lost in process of being drained away before reaching the target. some of the drug is lost before reaching target, and some is absorbed by tissues in the anterior chamber
what are enzymes involved in drug metabolisation
- esterases
- monoamine oxidase
what happens after the drug penetrates the cornea and is eliminated from aqueous humour
gets absorbed by tissue of the anterior uvea
factors influencing drug delivery to eye continued
blood aqueous barriers -
what does the blood aqeuous barrier do
limits the free access of systemic drugs to the anterior chamber
main component of blood aqeuous barrier?
- tight ciliary epithelium
- low permeability of iris blood vessels
when eye is inflamed BAB can break down and increase drug bioavailibilty
what is the blood-retinal barrier
a more significant barrier
- formed by tight junctions between capillary endothelial cells and retinal pigment epithelial cells
- limits the passage of all but smallest lipid soluble molecules
ophthalmic drug stability
- no drug is indefinetly stable
- drug should habe long shelf life
-once a multi dose bottle is opened drug is subject to oxidative damage and bacterial contamination
sterilisation method?
- heat
-sterile filtration
what do preservatives ensure
there is no microbial growth during lifetime of drug
