Drugs and the eye Flashcards
list the 3 routes of administration of drugs
- topical
- intra-ocular
- systemic
list the 3 forms of topical routes of drug administration and describe each form
- solutions: for drugs which are soluble
- suspensions: for drugs which are not soluble e.g. steroid eye drops, which is a hydrophobic molecule, the suspension is an emulsion i.e. yo shake the bottle and this puts the molecule back into the solution
- ointments: used to increase the duration/content on the ocular surface, but can make vision smeary
list the 2 forms of intra-ocular routes of drug administration and describe each form
- injection: e.g. lucentis which treats AMD
- insert: drug is impregnated into insert and then into the vitreous where it is released over time e.g. steroids or antibiotics
list the 2 forms of systemic routes for drug administration
- oral
- injection
list the 7 pharmacological/therapeutic classes of drug and what the use/formulation of the drug depends on
- anti-invectives
- corticosteroids/anti-inflammatory
- anti-glaucoma
- dry eye
- mydriatics/cycloplegics
- local anaesthetics
- peri-operative
depending on the site of action will determine how to formulate the drug
what is drug bioavailability determined by
the unique pharmacokinetic properties of the eye
name 3 factors that influence the delivery of topical drugs to the eye
- pre-corneal factors e.g. tear film
- corneal penetration e.g. via cornea
- inside the eye
what does a single drop from a conventional dropper bottle exceed
the capacity of the conjunctival sac
what has a major influence of the drug on pre-corneal retention time
the tear turn over rate
what pre corneal component exceeds corneal penetration, what implication does this have and how can it be reduced
- nasolacrimal drainage
- higher rates of drainage occur with larger drop sizes and this is vulnerable to being systemically absorbed across the nasal mucosa causing systemic toxicity
- putting pressure on puncta after instillation can avoid/reduce systemic absorption
what part of the eye is the main route of entry for topical medication
the cornea
which form of drugs penetrate the corneal epithelium and endothelium rapidly
lipid soluble drugs
what part of the cornea limits the passage of lipophilic formulations of drugs
the hydrophilic stroma
what type of drugs contributes to optimal corneal penetration
drugs which possess a combination of hydrophilic and hydrophobic properties
e.g. a weak acid depending on the pH it is in
what can influence the rate of drug penetration
ocular morbidity
where are the drugs distributed, following corneal penetration/inside the eye
into the aqueous humour
what occurs with the drug in the aqueous humour (inside the eye)
drug-target interaction
how are drugs eliminated from the anterior chamber (inside the eye)
by a combination of aqueous turnover and absorption across the tissues of the anterior uvea
_______ binding can also influence bioavailability inside the eye
melanin binding can also influence bioavailability inside the eye
what 2 things are involved in drug-target interaction
- enzymes
- receptors
which enzymes are involved with drug-target interaction
carbonic anhydrase inhibitors e.g dorzolomide
give 2 example of drugs which bind to receptors during drug-target interaction
- beta blockers e.g. timolol
- muscarinic e.g. cyclopentolate
give 5 examples of enzymes that are involved in ocular drug metabolism
- esterases
- monoamine oxidase
- N-acetyltransferase
- oxidoreductase
- catechol-O-methyltransferase
where in the eye are drug metabolising enzymes usually found and what happens to the drug as it passes through this structure
in the cornea
as the drug passes through the cornea it is acted upon by these enzymes and transformed chemically through its transit
during drug metabolism, some drugs are broken down by ocular tissues during penetration ________________________
limiting their effectiveness
what are some pathways during drug metabolism exploited by
exploited by pro-drugs
how do pro-drugs exploit some pathways during drug metabolism
where the breakdown product is more efficacious than the parent compound e.g. the anti-glaucoma drug latanoprost is metabolised by esterases on the transit through the cornea
how are drugs excreted following corneal penetration and distribution
drugs are eliminated from the aqueous humour, by a combination of aqueous turnover and absorption across the tissues of the anterior uvea
what is an additional factor to drug excretion which can influence bioavailability and may predispose to toxicity
drug binding to the pigmented tissues of the iris and ciliary body
list 3 factors influencing systemic drug delivery to the eye
- blood-ocular barriers
- plasma protein binding
- active transport
