Drugs And The Eye Flashcards
Name two examples of lubricants which optometrists prescribe.
Hypromellose and sodium hyaluronate
Name two anti-invectives which optometrists prescribe.
Fusidic acid and Chloramphenicol
Name two systemic drugs used for allergies.
Antihistamines such as Cetirizine and Loratadine.
What is the main type of drug administrated?
Topical
What are peri-operative drugs?
Drugs that are used straight after surgery
What are some pre-corneal factors of topical drugs ?
Tear turnover rate has great influence as sometimes nasolacrimal drainage can exceed corneal penetration which could lead to a higher risk of systemic toxicity which could also be increased due to larger drop sizes.
Larger drop size doesn’t necessarily mean more drainage due spillage.
What is the link between bioavailability and drop size from an eye drop?
Multiple drops or a larger drop size does not mean there is more bioavailability which shown my the plateau in the graph.
For glaucoma, beta blockers are administrated. What effect this does this have?
Beta receptors are blocked which reduces aqueous production in the eye.
Why should a drug have a combination of both hydrophilic and hydrophobic properties?
Hydrophilic so its able to pass through the stroma.
Hydrophobic so it is able to pass through the epithelium.
This influences the rate of drug penetration.
In its ionised form is a drug hydrophilic or hydrophobic?
Hydrophilic
When a molecule loses a protein does it become ionised or non-ionised?
Ionised
Can an ionised molecule penetrate the epithelium easily?
Yes
Describe the process of a molecule penetrating through the ocular surface.
Firstly it loses a protein to become ionised so it can penetrate the epithelium. It then gains a proton to become non-ionised to penetrate the stroma. It then lose a proton to be ionised to penetrate through to decements membrane. Finally it gains a proton to be back to its non-ionised form- can be pH driven
After corneal penetration, what happens to the drug and what can affect absorption after?
It goes to the target cells and then is eliminated through the anterior chamber by aqueous turnover and it is also absorbed through the tissues of anterior uvea. Melanin affects absorption (bioavailability) which is why a higher concentration may be required for darker irises.
Name some interocular targets.
-Muscranic receptors in the ciliary body
-Carbonic anhydrase inhibitors (Dorzolomide-used for angle open glaucoma)
Give an example of a pro drug and how metabolism effects the drug.
An example is a pro drug such as an anti-glaucoma drug. When it has come out the dropper it is inactive and not that effective. As it metabolises by the enzyme esterase it then becomes active.
How is an introcular drugs excreted?
-Eliminated by aqueous humour
-Absorbed by uvea tissue
Name three factors which effect the systemic drug delivery to the eye.
1) Blood-ocular barriers
2) Plasma protein binding
3) Active transport
Why is it difficult for systemic drugs to overcome the blood-aqueous barrier ?
It is limited due to the tight junctions (between capillary endothelial cells and RPE cells) and low permeability of iris blood vessels.
How is the blood-aqueous barrier overcome?
Sometimes drug transporters are used.
Not all drugs can do this such as anti-VEGF.
What is something a patient can do to maybe increase the absorption of a drug?
Put some pressure on the puncta after it has been administrated to give it a chance to be penetrated before it enters the nasolacrimal system.
Are drugs indefinitely stable?
No
What is a characteristic that is important in maintaining stability?
The pH of a drug- it retains solubility.
Are corticosteroids lippophillic or hydrophilic?
Lippophillic.
Once a multi dose bottle is open, what issues can come from this?
Oxidative damage and bacterial contamination.
How is a drug sterilised ?
Heating the drug without impacting its stability and force the drug through a sterile filtration
Once is a sterilised, what is put into a drug to ensure this is maintained?
Preservatives
What group of drugs are preservative free?
Intraocular drugs
Name six inactive ingredients which are used in ophthalmic formulations
-Buffers
-Preservatives
-Antioxidants
-Viscous agents
-Tonicity-adjusting agents
-pH adjusting agents
What do viscosity agents do to a formulation?
Thicken it
Name three antioxidants in drugs.
-EDTA
-Sodium bisulphite
-Sodium metabisulphite
Name the function of preservatives
Destroy or inhibit the growth of micro-organisms
Name three preservatives
- Benzalkonium chloride (BAK), this is the most common preservative used in ophthalmic drugs
- Phenylmercuric nitrate
-Polyquad - Newer less toxic include: Purite, Sofzia
Name some properties of BAK (benzalkonium chloride)
- Can affect corneal penetration
- Binds to hydrogel CLs (can be problematic)
- Excellent chemical stability
- Effective against GM+ve and GM-ve organisms
True or false: all preservatives are toxic.
True
