Ocular pharmacology Flashcards by Lucy Butler

Topical drug formulations

Drops
- solutions
- suspensions
- emulsions

Gel
- liquefy on contact with corneal surface

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

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Topical drug formulations - drop vs gel vs ointment

Drop:
- duration of action: short
- frequency of administration: high
- ease of application: easy
- lubricant effect? minimal

Gel:
- duration of action: medium
- frequency of administration: medium
- ease of application: easy
- lubricant effect? yes

Ointment:
- duration of action: prolonged
- frequency of administration: low
- ease of application: harder
- lubricant effect? yes

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Topical drug administration - how many drops should be applied at a time and why?

delivery volume of eye drops is 50µl (20 drops in 1ml)
only 20-30µl is retained on surface of eye
1 drop at a time

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Topical drug administration - how many minutes should be left between administration of different topical drugs?

5-10mins

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Topical ophthalmic antibiotics - examples

fusidic acid (Isathal)
chloramphenicol
ofloxacin (Exocin) & ciprofloxacin (Ciloxan)
gentamicin (Tiacil - drop, Clinagel - ointment)
Chlortetracycline (Ophtocycline)

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Fusidic acid (Isathal)
- spectrum of activity
- main indications
- intraocular penetration
- licensed (Y/N?)
- application frequency
- comments

Spectrum of activity
- mainly bacteriostatic, mainly G+ve bacteria

Main indications
- 1st line for minor ocular surface infections e.g. conjunctivitis

Intraocular penetration
- good

Licensed (Y/N?)
- yes

Application frequency
- 1-2x daily

Comments
- too narrow spectrum for corneal ulcers in brachycephalics

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Chloramphenicol
- spectrum of activity
- main indications
- intraocular penetration
- licensed (Y/N?)
- application frequency
- comments

Spectrum of activity
- bacteriostatic, broad spec (NB not Pseudomonas)

Main indications
- prophylaxis for ulcers and ocular sx, bacterial conjunctivitis

Intraocular penetration
- good

Licensed (Y/N?)
- no

Application frequency
- drops 4x daily
- ointment 2x daily

Comments
- low toxicity to corneal epithelium -> good for corneal ulcers

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Ofloxacin (Exocin) & ciprofloxacin (Ciloxan)
- spectrum of activity
- main indications
- intraocular penetration
- licensed (Y/N?)
- application frequency
- comments

Spectrum of activity
- bactericidal, broad spec (including G-ves / pseudomonas)

Main indications
- infected/melting corneal ulcers

Intraocular penetration
- good-fair

Licensed (Y/N?)
- no

Application frequency
- at least 4x daily (more for infected ulcer)

Comments
- not for general prophylaxis - reserve for infected ulcers
- some straps & streps resistant (important: these are common ocular pathogens)

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Gentamicin (Tiacil - drops, Clinagel - ointment)
- spectrum of activity
- main indications
- intraocular penetration
- licensed (Y/N?)
- application frequency
- comments

Spectrum of activity
- bactericidal, broad spec (including G-ves / pseudomonas)

Main indications
- infected/melting corneal ulcers

Intraocular penetration
- poor

Licensed (Y/N?)
- yes (2 products)

Application frequency
- drops: at least 3x daily (more for infected ulcers)
- ointment: 2-3x daily

Comments
- epitheliotroxic to corneal epithelium, often irritant

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Chlortetracycline (Ophtocycline)
- spectrum of activity
- main indications
- intraocular penetration
- licensed (Y/N?)
- application frequency
- comments

Spectrum of activity
- bacteriostatic, broad spec including Chlamydophila & mycoplasma (NB not pseudomonas)

Main indications
- feline chlamydial conjunctivitis

Intraocular penetration
- poor

Licensed (Y/N?)
- yes

Application frequency
- 4x daily

Comments
- relatively new product in UK
- questionable benefit to speed healing of SCCEDs

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Anti-collagenases - use, application frequency, examples

Used to tx melting (infected) ulcers

Apply every 1-2h for 24h then gradually reduce

Serum: from same or another animal
- take e.g. 10ml blood into serum tubes, leave to clot for 30mins
- spin down and extract serum, place in plain tubes/dropper bottles
- keeps in fridge for 1 week
- keeps in freezer for 6m

Stromease
- N-acetylcysteine
- fairly new product
- synthetic alternative to serum

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Systemic (oral) anti-bacterials with ophthalmic relevance

clindamycin
tetracyclines
sulphonamides
enrofloxacin

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Clindamycin
- spectrum of activity
- clinical indication
- comment

Spectrum of activity
- bacteriostatic, spectrum includes anaerobes & protozoa

Clinical indication
- toxoplasma gondii-induced uveitis in cats & dogs

Comment
- use at 25mg/kg/day PO in divided doses for feline toxoplasmosis

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Doxycycline
- spectrum of activity
- clinical indication
- comment

Spectrum of activity
- bacteriostatic, broad spec including Chlamydophila & Mycoplasma

Clinical indication
- feline conjunctivitis caused by Chlamydophila

Comment
- use 3-4w course to eradicate organism
- NB may cause enamel discolouration in young animals
- NB can cause oesophagitis -> ensure food/water intake afterwards

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Sulphonamides
- spectrum of activity
- clinical indication
- comment

Spectrum of activity
- bacteriostatic, broad spec

Clinical indication
- risk of KCS (dry eye) due to toxic effect on lacrimal gland -> may or may not be reversible

Comment
- monitor STT if using

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Enrofloxacin (e.g. Baytril)
- spectrum of activity
- clinical indication
- comment

Spectrum of activity
- bactericidal, broad spec

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

Comment
- if possible, avoid using in cats
- marbofloxacin (Marbocyl) is safe at routine doses

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Anti-viral drugs - use, forms

Used for feline herpesvirus-1 (FHV-1)

All drugs are virostatic not virucidal
- need regular application

Topical
- ganciclovir 0.15% (Zirgan) 4x daily, best topical option
- aciclovir 3% ointment (Zovirax) 5x daily, cheaper but questionable efficacy

Oral
- famciclovir tablets or oral past
- recommend dose currently 90mg/kg 2x daily (this may change due to ongoing research)
- expensive

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Anti-fungal drugs - use

Fungal ocular conditions are relatively uncommon in the UK but can sometimes cause an infected (melting) ulcer

Equine fungal keratitis&raquo_space; canine fungal keratitis

No commercially available topical preparations -> need to re-constitute alternative formulation

Seek specialist advice

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Topical anti-inflammatory and immunomodulatory drugs - examples

prednisolone acetate (Pred Forte)
dexamethasone (Maxidex)
diclofenac (Acular) and flurbiprofen (Ocufen)
ciclosporin

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Prednisolone acetate (Pred Forte)
- class
- mechanism of action
- corneal penetration
- indications
- comments

Class
- corticosteroid

Mechanism of action
- inhibit arachidonic acid formation: anti-inflammatory actions and immunosuppressive action at high doses

Corneal penetration
- good

Indications
- anterior uveitis & peri-op for cataract surgery (i.e. tx and prevent intraocular inflammation)

Comments
- contraindicated in corneal ulceration (can exacerbate collagenolysis)
- frequent use may cause systemic signs (e.g. PUPD)
- chronic use may induce corneal lipidosis

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Dexamethasone (Maxidex)
- class
- mechanism of action
- corneal penetration
- indications
- comments

Class
- corticosteroid

Mechanism of action
- inhibit arachidonic acid formation: anti-inflammatory actions and immunosuppressive action at high doses

Corneal penetration
- reduced

Indications
- immune-mediated ocular surface dz including chronic superficial keratitis (pannus) in dogs and eosinophilic keratoconjunctivitis in cats

Comments
- contraindicated in corneal ulceration (can exacerbate collagenolysis)
- frequent use may cause systemic signs (e.g. PUPD)
- chronic use may induce corneal lipidosis
- dexamethasone also available combined with antibiotics as “Maxitrol” but usually don’t need both drugs

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Diclofenac (Acular) and flurbiprofen (Ocufen)
- class
- mechanism of action
- corneal penetration
- indications
- comments

Class
- NSAID

Mechanism of action
- inhibit the COX pathway: anti-inflammatory action

Corneal penetration
- good

Indications
- treat & prevent intraocular inflammation, esp if corticosteroids contraindicated

Comments
- epitheliotoxic and delays corneal ulcer healing but safer than topical corticosteroid
- can increase IOP: use with caution in cats with glaucoma
- may inhibit platelet fx: care if intraocular haemorrhage present

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Ciclosporin
- class
- mechanism of action
- corneal penetration
- indications
- comments

Class
- calcineurin inhibitor

Mechanism of action
- reduce T lymphocyte activation -> immunosuppressive effect -> increases tear production in KCS, anti-inflammatory action to reduce scar tissue

Corneal penetration
- poor

Indications
- licensed for canine KCS (1st line tx) and chronic superficial keratitis (pannus)

Comments
- safe to use with corneal ulceration
- suitable for ocular surface dz only

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Production of aqueous humour

Study These Flashcards

by ciliary processes
diffusion, ultrafiltration and active secretion

Drainage of aqueous humour

- mostly by uveal trabecular meshwork (iridocorneal drainage angle - 'conventional pathway')

Anti-glaucoma drugs - options for how they work

Either reduce aqueous humour production OR increase aqueous humour outflow No licenced anti-glaucoma drugs for dogs/cats Drugs are produced for humans with different types of glaucoma - not always very effective in animals

Anti-glaucoma drugs - examples

- prostaglandin analogues (Latanoprost & Travoprost) - carbonic anhydrase inhibitors (Brinzolamide [Azopt] & Dorzolamide [Trusopt]) - beta blockers (Timolol)

Anti-glaucoma drugs - mechanism of action

Prostaglandin analogues - induces mitosis & increases uveoscleral outflow of aqueous humour Carbonic anhydrase inhibitors & beta-blockers - reduces aqueous humour formation by ciliary body

Prostaglandin analogues - drug of choice for...

- emergency tx of acute primary glaucoma - post-op ocular hypertension - chronic glaucoma -- most effective drug at reducing IOP, can reduce high IOP to safe level within 60-90mins of application

Prostaglandin analogues - frequency of application

- usually 2x daily

Prostaglandin analogues - use in cats

- ineffective in most cats

Why should prostaglandin analogues be used with caution if uveitis is present? What is another contraindication for the use of prostaglandin analogues?

- they can cause disruption of the blood-aqueous barrier - topical prostaglandin analogues cause marked mitosis and entrapment of the vitreous within the mitotic pupil, which can lead to a raised IOP, therefore they shouldn't be used in cases of anterior lens luxation

Carbonic anhydrase inhibitors - use

- may reduce IOP by ~20%, likely not enough on their own for primary glaucoma - okay to use in any type of glaucoma

Carbonic anhydrase inhibitors - frequency of application

- up to 3-4x daily

Carbonic anhydrase inhibitors - examples & their use

Brinzolamide (Azopt) - drug of choice in dogs - closer to physiological pH (7.5) Dorzolamide (Trusopt) - drug of choice in cats, as brinzolamide is less effective - more likely to cause irritation (due to pH of 5.6)

Beta-blockers - use & frequency of application

- Timolol most commonly used - relatively small effect on IOP on its own but may have additive effect when used with other drugs - use 2-4x daily

Beta-blockers - potential systemic side effects

Bradycardia and hypotension - care in cats/small dogs - care with cardiovascular dz

Use of osmotic diuretics as an anti-glaucoma drug

Osmotic diuretics (e.g. mannitol IV over 30mins) were traditionally 1st line tx for acute glaucoma - however significant risk of side effects and now infrequently used - superseded by topical meds

Tear substitutes (lacrimomimetics) - use

- often used in conjunction with a lacrimostimulant (e.g. ciclosporin) - the ideal lacrimomimetic should mimic the trilaminar tear film as closely as possibly - hundreds of products available, choice may depend on -- O factors e.g. ease of administration, frequency of administration -- pt factors e.g. severity of condition, most appropriate constituents for the individual

How lacrimomimetics replace the tear film

Aqueous tear substitutes (drops) - include cellulose polymers e.g. hypromellose and vinyl derivates: short Lipid-based ointments - containing lanolin, petrolatum and/or mineral oil - prevent tear film evaporation - excellent corneal retention Mucinomimetics (gels) containing polyacrylic acid (carbomer) AND viscoelastic (drops) containing hyaluronic acid - highly effecitve - prolonged corneal retention

Aqueous tear substitutes - duration of action, use

- short-acting (<20mins) - not useful for KCS tx - useful as vehicle to deliver compounded drugs

Mucomimetics - frequently of application, duration of action

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

Viscoelastics - frequently of application, duration of action

- easy to apply drops - last 4-6h - use 2-6x daily

Lipid-based - frequently of application, duration of action

- long acting (8-12h) - use 1-4x daily - useful overnight - some O find hard to apply - may blur vision

Use of mydriatics

Dilate the pupil, needed for - diagnostic purposes: examining lens and fundus - therapeutic purposes: treating anterior uveitis and aiding intraocular sx

Use of cycloplegics

- relax the ciliary body musculature - therapeutic purpose: relieving the painful ciliary spasm associated with anterior uveitis and helping reduce formation of posterior synechiae (adhesions)

Mydriatics & cycloplegics - examples

- atropine - tropicamide - phenylephrine

Atropine - mechanism of action - speed of onset - duration of action - mydriatic effect - cycloplegic effect

Mechanism of action - parasympatholytic (anticholinergic) Speed of onset - 1h Duration of action - 3-5d+ Mydriatic effect - yes Cycloplegic effect - yes

Tropicamide - mechanism of action - speed of onset - duration of action - mydriatic effect - cycloplegic effect

Mechanism of action - parasympatholytic (anticholinergic) Speed of onset - 30mins Duration of action - 8-12h Mydriatic effect - yes Cycloplegic effect - minimal

Phenylephrine - mechanism of action - speed of onset - duration of action - mydriatic effect - cycloplegic effect

Mechanism of action - sympathomimetic (adrenergic) Speed of onset - 20mins-1h Duration of action - 12-18h Mydriatic effect - yes Cycloplegic effect - no

What mydriatic would you use to dilate the pupil to aid fundus examination and why?

- phenylephrine - quick speed of onset

What mydriatic is most commonly used to treat anterior uveitis and why?

- atropine - it is both a mydriatic and a cycloplegic agent

What are the side effects of and contraindications for the use of atropine?

- sensitivity to bright light - blurred vision - irritation - excess salivation (esp in cats) - decreased GI motility - increased HR

What mydriatic can be used to diagnose Horner's syndrome?

- phenylephrine

Local anaesthetics - how do they work?

- act as sodium channels to reversibly block afferent and efferent nerve impulses

What are topical LAs used for analgesia for?

- diagnostic procedures e.g. tonometry, ocular US - minor surgical procedures e.g. grid keratotomy

What are injectable LAs used for?

- orbital anaesthesia -- most commonly for enucleation

Topical LA - most commonly used example - onset of action - duration of action - side effects / contraindications

- proxymetacaine (proparacaine) most commonly used in practice - rapid ones (within 1min) - lasts approx 45mins - repeat application beneficial: 2-3 drops over 2-3mins, increases depth and duration of anaesthesia - don't use therapeutically as epitheliotoxic i.e. delays corneal healing - don't apply before STT, will block reflex tear production

Injectable local anaesthetics - examples, their onset & duration of action, and their use

Lignocaine - lidocaine, 1-2% - acts in 10mins - lasts 60mins Bupivicaine - 0.25-0.75% - acts in 45mins - lasts for 6h Clinical use: enucleation - retrobulbar injection of a combined solution of lignocaine and bupivicaine (1-3ml, 1:4 ratio) provides good peri/post-op analgesia - splash block can be used as technically easier alternative

Ocular pharmacology Flashcards

(59 cards)