Ocular Pharmacology Flashcards
A) What is the delivery volume for an eye drop?
B) How much is retained on the eye?
A) 50μl
B) 20μl
What is the issue of giving more than 1 drop? What can be done to help this?
- >1 drop simulates reflex tearing and dilution effect!
- Allow 10-15 minutes between administration of different topical drugs
Name 3 common topical anti-bacterials (5)
- Fusidic acid
- Chloramphenicol
- Fluoroquinolones
–Ofloxacin
–Ciprofloxacin
•Aminoglycosides
–Neomycin
–Gentamycin
•Cloxacillin
Fusiidic Acid:
A) Where has it got goood activity?
B) What is it poor against?
A) Gram +ve activity, especially Staphylococcus sp which are common in eye
B) Against Chlamydophila felis and Pseudomonas sp
Name 2 posiitive of using fusidic acid? (4)
- Good corneal penetration
- Gel/drop formulation easy to use
- Once daily dosing, good owner compliance
What is fusidic acid a good first line defence for?
Topical antibiotic for minor ocular surface infections e.g. conjunctivitis
Why can we not use fusidic acid for cornal ulcer in brachycephalic dogs?
Narrow spectrum
What is this?
Stromal ulcer
Chloramphenicol:
A) What spectrum?
B) What has it go poor efficacy against?
A) Broad including anaerobes
B) Against Chlamydophila felis and Pseudomonas sp
Name 2 positives of using chloramphenicol (4)
- Good corneal penetration
- Good choice for ocular surface disease, especially dogs, ocular surgery and penetrating corneal trauma
- Low toxicity to corneal epithelium therefore good for corneal ulcers
- Available in drops and ointment formulations
Name an example of a flueorquinolone (2)
- Ofloxacin (Exocin®)
- Ciprofloxacin (Ciloxan®)
Fluoroquinolone:
A) What is it effective?
B) What is it resistant against?
A) Effective against Gram-ve and some Gram+ve organisms
B) Some Staphylococcal sp and Streptococcal sp may be resistant
Aminoglycosides:
A) What is it effective against?
B) What is it commonly used for?
A) Gram-ve and some aerobic Gram+ve organisms
B) Pseudomonas sp
Name an example of an aminoglycoside (2)
- Gentamycin (Clinagel®, Tiacil®)
- Neomycin
What is neomycin often combined with?
Topical steroid
Name 2 problems of using gentamycin (aminoglycoside) (3)
- Epitheliotoxic to corneal epithelium
- Often irritan
- Toxic to the epithelium
What i gentamycin (aminoglycoside) superseded by?
Fluoroquinolone
Cloxacilin:
A) What is it resistant to?
B) What is it commonly used for?
A) Beta-lactamase-resistant penicillin(bactericidal)
B) Topical antibiotic routinely used for infectious bovine keratoconjunctivitis (IBK); readily available
How do you do a subconjunctival injection?
Include needle type etc.
- Injection of drug under bulbar conjunctiva
- Slow release of drug, reduces labour intensity of treatment
- Topical anaesthetic eye drops
- 24-27 gauge needle
- 0.5-1ml produces obvious ‘bleb’ at injection site
What is a subconjunctival injection commonly used for?
•Most common application is long-acting antibiotic in cattle
–IBK (infectious bovine keratoconjunctivitis)
–Penicillin G
Name 2 systemic anti bacterials useful to the eye (4)
- Clindamycin
- Tetracyclines
- Sulphonamides
- Enrofloxacin
Clindamycin:
A) What type of antibiotic?
B) What is the action?
C) What is it effective against?
A) Macrolide antibiotic
B) Bacteriostatic
C) Effective against Toxoplasma gondii, a cause of feline and canine uveitis
What is the treatment choice for feline chlamydial infection?
Doxycycline
Name a disadvantage of using tetracyclines e.g. Doxycycline (2)
Can discolour enamel of teeth in young animals
Can cause oesophagitis, essential to give with water
What is this?
Chlamydophila felis
What can sulphonamides cause and how?
•Can cause keratoconjunctivitis sicca (dry eye) due to toxic effect on lacrimal gland
Name 2 things which should be monitored when using sulphonamides
- Monitor STT
- Monitor tear production
What is the pharmacokinetics of using enrofloxacin (fluroquinolone) in cats?
Narrow therapeutic index
Name 2 issues of using fluroquinolones (3)
- Can cause permanent blindness due to retinal toxicity
- Rare but serious complication
- Do not use in cats
Is equine or canine keratomyosis more common?
Equine
Why do anti viral drugs need to be applied 5-6 times a day?
They are virostatic
Name topical (2) and oral (1) treatments for Feline Herpes Virus 1
•Topical
–Ganciclovir 0.15% (Zirgan®)
–Aciclovir 3% ointment (Zovirax)
•Oral
–Famciclovir tablets
–Recommended dose varies frequently because of ongoing research; current dose is 90mg/kg bid
–Expensive but generic form now available
Name 2 extraocular immune mediated disease which will need to be treated with anti-inflammatory drugs (3)
- Keratoconjunctivitis sicca (dry eye)
- Feline eosinophilic keratoconjunctivitis
- Chronic superficial keratitis (‘pannus’)
Name a intraocular immune mediated disease which requires anti-inflammatory drugs
Uveitis
Where are topical steroids contra-indicated? Why?
Corneal ulcers
–Steroids exacerbate collagenolysis, leading to corneal perforation
What is dexamethasone good for?
Occular surface disease e.g. Pannus
What is prednisolone acetate good for?
Intraocular disease e..g. uveitis
What is the issue of usng topical NSAIDs with a corneal ulcer?
Epitheliotoxic and delay healing of corneal ulcers
Name a time topical NSAIDs are good (2)
- Uveitis
- Intraocular surgery
Name a topical NSAID (2)
•Ketorolac trometamol
–Acular®
–Most commonly used in general practice
•Flurbiprofen
–Ocufen®
How does cyclosporine work?
T cell suppression (inhibit interleukin 2)
Name 3 actions of cyclosporine (4)
•Increases tear production
–mainstay in the management of KCS (dry eye)
•Anti-inflammatory action
–Reduces scar tissue on ocular surface (corneal pigmentation and vascularisation)
- Safe to use with corneal ulceration (even if a ‘dry eye’ ulcer is present)
- Poor corneal penetration so suitable for ocular surface disease only
Name immunomodulatory drugs and the action?
- Calcineurin inhihibitors, reduce TH (T-Helper) lymphocyte activation
- Ciclosporin
What are immunomodulatory drugs first line treatment for?
Canine KCS
What are the 2 ways anti-glaucoma drugs reduce pressure?
•Reduce aqueous humour production
OR
•Increase aqueous humour outflow
How do carbonic anhydrase inhibitors work?
•Enzyme carbonic anydrase catalyses reaction in ciliary body to form aqueous humour
CO2 + H20 HCO3- + H+
•CAIs inhibit this reaction and therefore reduce the formation of aqueous humour which in turn reduces the IOP
Why have systemic carbonic anhydrase inhibitors been superseded by topical CAI?
Due to the systemic side effects
Name a Carbonic anhydrase inhibitors (CAIs) (2)
- Dorzolamide
- Brinzolamide
Dorzolamide 2%:
A) What is it effective in?
B) What can we combine with?
C) Why dont we use in an emergency?
A) Dogs and cats
B) Anti-glaucoma
C) Doesn’t reduce pressure much
Why is Brinzolamide 1% well tolerated?
Neutral pH
A) How do adrenergic agents work?
B) What is the effect?
C) What is caused?
D) When do we NOT use it?
A) Beta block
B) Reduce aqueous humour
C) Miosis
D) Bradycardia
Is prostglandin analogues ineffecive in cats and dogs?
Cats
How do prostaglandin analogues work?
- Reduces high IOP to safe level within 60-90 minutes of single application
- Applied 1-2 times daily
Where are prostaglandin analogues contraindicated and why?
•Contraindicated in uveitis and anterior lens luxation due to effect on pupil
–Uveitis – small pupil anyway
–Lens can get trapped in anterior chamber with a small pupil
Name a prostaglandin analogue (2)
- 0.004% travoprost (Travatan)
- 0.005% latanoprost (Xalatan)
What is the traditional first line treatment for glaucoma?
Osmotic diuretics
What do osmotic diiuretics cause?
Renal and cardiac function
What do osmotic diuretics do?
•Reduces IOP within 1hr and effect can last for up to 24 hours
What are the 3 layers and the way in which tear substitutes work?
- Aqueous layer → aqueous drops
- Mucin layer → mucinomimetic
- Lipid layer → lipid-based ointments
What are tear substitutes often used in conjuction with?
Lacrimostimulant e.g. cyclosporine
Name considerations when choosing a lubricant
- Literally 100s available OTT
- Drops vs gel vs ointment
- Drops last <20mins
- Gels last a few hours
- Ointments last several hours
Why cant we use aqueous tear substitues for?
•Canine KCS (keratoconjunctivitis sicca) generally too severe to make these drugs beneficial
What are aqueous tear substitues good for?
Flushing thick ocular discharge from affected dry eyes
What are aqueous tear substitutes?
- Methylcellulose
- Polyvinyl alcohol
- Short-acting < 20mins
- High frequency of administration
Name 2 mucinomimetics (gels) (3)
- Linear polymers (dextran, polyacrylic acid, polyinylpyrrolidone)
- Carbomer 980
- Viscoelastics (hyaluron derivative)
What can we combine Mucinomimetics (gels) with?
Aqueous substitutes
What is the minimum duration of Mucinomimetics (gels)?
4-6 hours
What are Lipid-based tear substitutes
(ointments) good for?
Protection during GA and for dry eye management
How ofteen do you apply Lipid-based tear substitutes
(ointments)?
1-4 x daily
how do Lipid-based tear substitutes
(ointments) work?
Prevent evapoation of tear film
Name a Lipid-based tear substitutes
(ointments) (3)
•Lanolin, petrolatum, mineral oil
What do mydriatics do and when are they used?
•Mydriatics dilate the pupil
–Diagnostic purposes (examine lens, fundus)
–Therapeutic purposes (intraocular surgery, uveitis)
What do cycloplegics do and when are they used?
•Cycloplegics relax ciliary body musculature
–Relieve painful ciliary spasm associated with anterior uveitis
–Therapeutic use only
Tropicamide (Mydriacyl®):
A) What type of drug is it?
B) What is the effect?
C) What is the onset?
D) What is the main use?
A) Parasympatholytic drug
B) Mydriatic >> cycloplegic effect
C) Rapid onset (30 minutes) and short duration (8-12 hours)
D) Main use is for diagnostic purposes
Atropine:
A) What type of drug is it?
B) What ar the effects?
C) What is the onset?
D) What iis the main onset?
A) Parasympatholytic drug
B) Mydriatic and cycloplegic effects
C) Slow onset (60 minutes) and long duration (60-120 hours)
D) Main use is for therapeutic purposes
Name 2 side effects of atropine (3)
•Reduces tear production
–Care in animals with dry eye and brachycephalic breeds
•Raises IOP
–Contra-indicated in glaucoma
•Systemic effects
–Hypersalivation due to bitter taste
–Tachycardia, constipation (uncommon but care if low bodyweight)
–NB colic in horses
What are local anaesthetic?
Weak bases that reversibly block afferent and efferent nerve impulses
What are topical local anaesthetics used for?
–Diagnostic procedures
•E.g. tonometry, ocular ultrasound
–Minor surgical procedures
Topical local anaesthetic:
A) How quickly does it act?
B) How long does it last?
A) Rapidly
B) Approx 30 minutes
Name an occasion we do not use topical local anaestheitc (2)
- Do not use therapeutically as epitheliotoxic i.e. delay corneal healing
- Do not apply before STT as will block reflex tear production
Name an injectable local anaesthetic and the use (2)
•Lignocaine (lidocaine, 1-2%) acts in 10 minutes and lasts 60 minutes
–Used for nerve blocks
•Bupivicaine (0.25-0.75%) acts in 45 minutes and lasts for 6 hours
–Used for post-operative analgesia
