Ocular Pharmacology

what types of topical drugs are used for ocular disease?

drops- solutions, suspensions, emulsions

gel- liquefy on contact with corneal surface

ointment- paraffin based, can be toxic to anterior segment (avoid in corneal or scleral perforations)

what is the delivery volume of eye drops and how much is acutally retained?

50ul- only 20-30 ul is retained on the eye surface

how many drops should be applied at once and why?

a single drop as that is a single dose

how many minutes should be left between administration of different drugs?

5 minutes to prevent washout of the first drug by the second

how should topical drugs be administered?

what is the action of fusidic acid and the main indication for use?

bacteriostatic, mainly G+ve bacteria

prophylaxis for ulcers, occular surgery and bacterial conjunctivitis

has good intraocular penetration

is fusidic acid licenced, what is the application frequency and why can't it be used in bracycephalics?

yes

1-2x daily

too narrow spectrum for corneal ulcers in brachycephalics

what is the action of chloramphenicol and the main indication for use?

bacteriostatic, broad spectrum but not for pseudomonas

first line for minor ocular surface infections

good intraocular penetration

is chloramphenicol licenced, how often is the application and why is it good for corneal ulcers?

in dogs but not cats

drops 4x daily, ointment 2x daily

low toxicity for corneal epithelium so good for corneal ulcers

what is the action of ofloxacin (exocin) and ciprofloxacin (ciloxan) and the main indication for use?

bactericidal, broad spec including G+ve such as psudomonas

used for melting ulcers

fair intraocular penetration

is exocin/ciloxan licenced for use, what is it's application frequency and why is it not used for general prophylaxis?

no

at least 4x daily (more for infected ulcer)

reserve for infected ulcers

some staph and streps are resistant

what is the activity and indications for use of gentamicin (tiacil drops/clinagel ointment)?

bactericidal- broad spec including pseudomonas

infected/melting corneal ulcer

poor intraocular penetration

is gentamicin licenced for eye use in animals, how often is application and what effect does it have on corneal epithelium?

yes

drops at least 3x daily, more for infected ulcers

ointment 2-3x daily

epitheliotoxic to corneal epithelium so often irritant

what is the activity of chlortetracycline (ophtocycline) and the main indications for use?

bacteriostatic, broad spec including chlamydophilia and mycoplasma

poor intraocular penetration

is chlortetracycline licenced in animals for eyes, how frequent is application and what is a benefit of this?

yes

4x daily

new product- questionable benefit to speed healing of SCCEDS

what is anti-collagenases used to treat and what is the application frequency?

used to treat melting (infected) ulcers

apply every 1-2 hours for 24 hours then gradually reduce

what anti-collagenases can be used?

serum from same or another animal

stromease- N-acetylcysteine, fairly new product, synthetic alternative to serum

what are the 4 main systemic antibacterials relevant to ophthalmology?

clindamycin

tetracyclines

sulphonamides

enrofloxacon

what is the action and clinical indication for clindamycin?

bacteriostatic, spectrum includes anaerobes and protozoa

toxoplasma gondii induced uveitis

use at 25mg/kg/day PO individed doses for feline toxoplasmosis

what is the action of doxycycline and it's clinical indication?

bacteriostatic, broad spectrum including chlamydophilia and mycoplasma

feline conjunctivitis caused by chlamydia

use 3-4 week course

what is a side effect of taking doxycycline?

can cause enamel discolouration in young animals

can cause oesophagitis- ensure food/water intake afterwards

what oral antibacterials can cause ocular toxicity?

sulphonamides

enfloxacin

what is the action and potential toxicity of sulphonamides?

bacteriostatic, broad spectrum

risk of KCS due to toxic effect on lacrimal gland that may or may not be reversible

monitor STT if using

what is the activity of enrofloxacin and it's potential toxicity?

bactericidal, broad spectrum

narrow therapeutic index in cats- can cause acute retinal degeneration (permenant blindness) when used at higher doses- rare but serious

therefore avoid using if possible in cats- marbofloxin is safe at routine doses

what drugs are used to treat ocular symptoms for FHV-1?

virostatic antiviral drugs

topical:

- ganciclovir 0.15% (Virgan) 4x daily, lower cost, availaible

- cidofovir - drops bID, expensive, available as special vet formulation

oral:

- famciclovir tablets or oral paste at 90mg/kg lower dose 50mg/kg SID

what anti-fungal drugs exist for ocular disease?

none- seek specialist advice - need to reconstitute alternative formulation v

what condition can fungi cause?

- melting ulcer

- equine fungal keratitis >> canine fungal keratitis

what class are prednisolone and dexmethasone and what is their mechanism of action?

corticosteroids

inhibit arachidonic acid formation, anti-inflam action and immunosuppressive action at high doses

what is the corneal penetration and indications for use of prednisolone?

good corneal penetration

immune mediated ocular surface disease including chronic superficial keratitis in dogs and eosinophilic keratoconjuncitivits in cats

what is the corneal penetration and indication for use of dexamethasone?

reduced corneal penetration

anterior uveitis and peri-operative for cateract surgery e.g. treat and prevent intraocular inflammation

when is prednisolone and dexamethasone contraindicated?

corneal ulceration

frequent use can cause systemic signs such as PUPD

chronic use may cause corneal lipidosis

what class of anti-inflam drug is diclofenac and flurbiprofen?

what is their mechanism of action

NSAID

inhibits COX pathway- anti-inflam action

what is the corneal penetration for diclofenac and flurbiprofen, the indications for use and side effects seen?

good corneal penetration

treat and prevent intraocular inflammation, especially if corticosteroids are contraindicated

epitheliotoxic and delays corneal ulcer healing, can increase IOP, may inhibit platelets

what class of drug is ciclosporin and what is it's mechanism of action?

calcineurin inhibitor

reduces T lymphocyte activation- immunosuppressive effect- increases tear production in KCS, anti-inflam action to reduce scar tissue

what is the corneal penetration of ciclosporin, indications for use and can it be used for corneal ulceration?

poor corneal penetration

licensed for canine KCS (dry eye- first line treatment) and chronic superficial keratitis (pannus)

safe to use with corneal ulceration, suitable for ocular surface disease only

what is the action of anti-glaucoma drugs and which are licensed for dogs and cats?

reduce aqueous humour production or increase aqueous humour outflow

no licensed products!

what are the 2 anti-glaucoma drugs used?

carbonic anhydrase inhibitors

beta blockers: timolol

prostaglandin analogues

what is the action of carbonic anhydrase inhibitors and beta blockers (timolol)?

reduces aqueous humour formation by ciliary body

what is the action of prostaglandin analogues?

induce miosis and increase uveoscleral outflow of the aqueous humour

what are prostaglandin analogues the drug of choice for?

emergency treatment of acute primary glaucoma

postoperative ocular hypertension

chronic glaucoma

very effective at reducing IOP

use 2x daily

INEFFECTIVE IN CATS

what prostaglandin analogues are most commonly used?

latanoprost

travoprost

why should prostaglandin analogues be used with caution of uveitis is present?

reported to induce recurrent uveitis

what is a contraindication of prostaglandin analogues?

can disrupt the blood aqueous barrier

can lead to raised IOP if entrap vitreous within myotic pupil

should not be used with anterior lens luxation

how often can carbonic anhydrase inhibitors be used and what are some examples?

3-4x daily

brinzolamide (azopt)- dog choice of drug

dorzolamide (trusopt)- cat choice of drug

can use for any glaucoma

what effect do beta blockers have on IOP, what is an example and what is the frequency of application?

small effect on IOP on own but have additive effects when used with other drugs

timolol

2-4 times daily

what are some potential systemic side effects of beta blockers?

bradycardia and hypotension- care with cardiac patients and in cats/small dogs

what are some combinations of anti-glaucoma drugs?

latanoprost and timolol

dorzolamide and timolol= cosopt

what are lacrimomimetics?

tear subsitutes

often used with a lacrostimulant e.g. cyclosporin

what are the 3 types of lacrimomimetics?

lipid based ointments

aqueous tear substitues

mucinomimetics

where do lipid based ointments target to replace the tear film?

lipid layer

contain lanolin, petrolatum and/or mineral oil

prevent tear film evaporation

excellent corneal retention

where do aqueous tear substitutes target to replace the tear film?

drops at aqueous layer

contain cellulose polymers e.g. hypromellose and vinyl deratives

short duration of action

where do mucinomimetics work to replace the tear film?

gels at mucous and aqueous layer

contain polyacrylic acid (carbomer) and viscoelastics (drops) containing hyaluronic acid

highly effective and prolonged corneal retention

what are the different classes of lacrimomimetics?

aqueous tear substitutes

mucinomimetics

viscoelastics

lipid based

how long do aqueous tear substitutes last and what is an example?

short acting- less than 20 mins so not for KCS

isopto 0.5%

hypreomellozs

how long do mucinomimetics last and what is an example?

easy to apply gel, lasts 4-6 hours, use 2-6x daily

carbomer eye gel 0.2%

viscotears liquid gel

Ocry-gel

how long do viscoelastics last and what is an example?

easy to apply drops

last 4-6 hours, use 2-6x daily

hyloforte

remend corneal repair gel

how long do lipid based lacrimomimetics last and what is an example?

long acting- 8-12 hours, use 1-4x daily, good for overnight

may blur vision and can be hard to apply

vitA-POS

lacrilube

Xailin night

what is the use of mydriatics?

dilate the pupil

used for diagnostic purposes for examining lens and fundus

therapeutic purposes- treating anterior uveitis and aiding intraocular surgery

what is the use of cycloplegics?

relax the ciliary body musculature

therapeutic purpose- relieve painful ciliary spasm associated with anterior uveitis and helping reduce formation of posterior synechiae (adhesions)

what are some mydriatic and cycloplegic drug examples?

both- atropine, tropicamide

only mydriatic- phenylphrine

what is the mechanism of action of atropine and speed of onset?

parasympathetic (anticholinergic)

onset in 1 hour

what is the duration of atropine action and what effect does it have?

3-5 days

mydriatic and cycloplegic

what is the mechanism of action of tropicamide and the speed of onset?

parasympathetic (anticholinergic)

30 minute onset

what is the duration of action for tropicamide and what effect does it have?

8-12 hours

mydriatic effect and minimal cycloplegic effect

what is the mechanism of action and the speed of onset for phenylephrine?

sympathetic (adrenergic)

20 mins to 1 hour

what is the duration of action of phenylephrine and what effect does it have?

12-18 hours

only a mydriatic effect

what mydratic would you use to dilate the pupil for fundus examination?

tropicamide

what mydratic is most commonly used to treat uveitis?

atropine applied every 24-48 hours

what are the side effects and contraindications of using atrophine?

skin around eyes may become sore, swollen, red and itchy

dry mouth

hypersalivation

with overuse/prolonged use- increased body temp, constipation, tachycardia

what mydriatic agent is used to diagnose Horner's syndrome?

Phenylephrine 1% topical

how do local anaesthetics work?

act at sodium channels to reversibly block afferent and efferent nerve impulses

what ocular procedures involve topical local anaesthetics?

diagnostic procedures e.g. tonometry

minor surgical procedures e.g. grid keratotomy

when are injectable local anaesthetics used?

for orbital anaesthesia for enucleations

what is an example of a topical local ocular anaesthetics and some considerations for use?

proxymetacaine (proparacaine)

rapid onset within 1 min

lasts 45 mins

repeat application can be beneficial

don't use therapeutically- endotheliotoxic

when should you apply topical local anaesthestics?

do not apply before STT; will block reflex tear production

what is an example of injectable local anesthetic for eyes?

lignocaine (lidocaine, 1-2%) acts in 10 mins and lasts 60 mins

bupivicaine (0.25-0.75%) acts in 45 mins and lasts for 6 hours

clinical use- enucleation