Pharmacology for the eye Flashcards
What are the 7 things a vet should know about drugs for the eyes?
- How to control pain to examine cornea
- Routes for medications to infiltrate ocular
structures - Selection of topical ocular and systemic anti‐
infectives - Topical antivirals for active herpes
- Selection of topical anti‐inflammatories &
immunosuppressive drugs - Medication to change pupil diameter
- Medication to reduce pressure in anterior
chamber
What topical drug can be used to control pain to examine the cornea?
- Local anaesthetic drops = lignocaine opthalmic drops. Rapid onset and duration of around 30-120 mins.
- This may be insufficient due to the severity of pain. Sedation or general anaesthesia may be required
What barriers are there in the eye?
- Blood-ocular barriers -> the blood-aquesous barrier and the blood-retinal barrier
What is an amphipathic drug?
Able to cross lipid and water
What are the three routes of topical ocular and systemic administration?
- Across the cornea
- Absorption by conjuntival blood vessels that flow into the ciliary body
- Drug exit via nasolacrimal duct
What are the three routes of topical ocular and systemic administration?
- Across the cornea
- Absorption by conjuntival blood vessels that flow into the ciliary body
- Drug exit via nasolacrimal duct
For topical formulations, how much drug is required to be effective?
- Only 10 – 25 uL are retained in conjunctival fornix & tear film after immediate overflow
- Commercial droppers deliver 25 – 50 µL of drug formulation / drop -> thus 1 drop is sufficient
- Best to use less more frequently
- After 5 minutes only 20% of drug remains on the ocular surface (as some drug may go through cornea, absorbed by blood vessels or goes out nasolacrimal drainage into the mouth).
How would you treat a sterile corneal ulcer?
Using proteinase inhibitors such as tetracycline or acetylcysteine drops to inhibit corneal proteolytic activity
How would you treat a traumatic or infected corneal ulcer in a dog?
Use an ointment that covers gram positives and gram negatives (something like tricin).
- Gram positives = bacitracin
- Gram negatives = polymixin or aminoglycosides
How would you treat a traumatic or infected corneal ulcer in a dog?
Use an ointment that covers gram positives and gram negatives (something like tricin).
- Gram positives = bacitracin
- Gram negatives = polymixin or aminoglycosides
What is the issue with using topical tetracycline eye ointment?
- Topical tetracyclines can irritate the cornea
- Currently only available through compounding pharmacies
How would you treat ocular signs associated with mycoplasma felis?
- Tetracycline ointment OR systemic therapy such as orla doxy or fluoroquinolones
How would you treat ocular chlamydiosis?
- Treated as for Mycoplasma spp.
- Tetracycline ointment OR systemic therapy such as orla doxy or fluoroquinolones
- NOTE: Doxycycline can be administered to kittens and pups > 4 weeks old without enamel discolouration
What are the topical anti-viral eye formulations that are available?
- Trifluridine - irritates cornea
- idoxuridine - drops do not penetrate the conjunctiva and cornea well except where there is ulceration
- cidofovir - BID drops. Carcinogenic.
Can antivirals eradicate latent infections?
- They are virostatic ‐ this means they are only effective in treating actively replicating virus and cannot eradicate latent infections
In what circumstance would you use a glucocorticosteroid?
- to delay healing such as reducing corneal scar tissue and optimise corneal opacity ‐ used only after the infection is eradicated.
- Would be used alongside an antibiotic (joint formulations (chloropstsone) are available
What is the difference between chloroptsone and chloropt?
Chloroptsone = chloramphenicol with GCS
Choropt = chlorampenicol ONLY
What is an example of an immune mediated ocular disease and how might it be treated?
- Pannus (chronic superficial keratitis)
- Treatment: topical GCS but requires continual therapy
How would you treat ‘dry eye’ or keratoconjunctivitis sicca?
- Use an immunosuppresive drug
- +/- antibacterial
- artificial tears
What do GCS such as prednisolone and dexamethasone do in the eye?
Immunosuppressive - inhibits T lymphocyte and macrophage action
What is the mechanism of action of steroid sparing drugs such as cyclosporine and tacrolimus?
Inhibit T lymphocyte action
What is mydriasis?
To dilate pupil
What is myosis?
To constrict pupil
What are some drugs that dilate the pupil (mydriatic) and what might it be used to examine?
- Muscarinic receptor antagonist such as atropine
- Used to examine the retina and fundus
What are some drugs that constrict the pupil?
- muscarinic receptor agonist such as pilocarpine
What are some drugs that reduce pressure in the anterior chamber?
- Carbonic anhydrase inhibitors such as dorzolamide or acetazolamide.
- Topical beta blockers (on ciliary epithelium) = timolol maleate
