Ocular pharmacology Flashcards
How can drugs be administered for ocular purposes
Topical
Systemic
What are the advantages of topical administration?
Convenient
Sometimes easy?
Minimal systemic side effects
Topical drugs are distributed in the eye in 3 ways. What are these?
Drainage by lacrimal drainage system
Penetration of eye via cornea/sclera
Through conjunction and nasal mucosal vessels
When topical drugs are distributed via nasal/conjunctival mucosa, were do they go? What is the efficacy of this?
Systemic circulation
Like slow IV
What are the disadvantanges of topical administration?
Drops are bigger volume than palpebral fissure can hold - excess spills out
15% tear film turned over/min - rapidly removed from surface
Poor bioavailability - only fraction of drug reaches anterior chamber
How can the bioavailability of topical drugs be improved in the eye?
Increase drug retention on palpebral fissure
Increase ability to penetrate cornea
What type of topical treatments can be applied to the eye?
Solution Suspension Ointment Viscous fluid/gel Colloidal system Subconjunctival injection
What is it called when drugs bind to tear film? What conditions is this suitable for?
Bioadhesion Dry eye (keratoconjunctivitis sicca)
Why is corneal penetration and absorption of ocular drugs limited?
Tight junctions in corneal epithelium - limit paracellular absorption
Topical corneal drugs can be lipid soluble or water soluble (should be both!). What parts of the cornea do they cross?
Lipid soluble -cross epithelium
Water soluble - cross stroma
When drugs penetrate the cornea, what structures of the eye do they go to? Which structures receive low levels of corneally absorbed drugs?
Aqueous humor, iris, ciliary body
Lens, vitreous humor and posterior segment receive little of drug
Non-corneal penetrative drugs enter the eyeball via the conjunctiva and sclera.. Are theses drugs hydrophilic or lipophilic?
Hydrophilic
Conjunctiva epithelum and sclera more permeable corneal epithelium
When drugs enter the eye via the sclera, where do they go?
Posterior segment or scleral vessels and ciliary body
Drug level higher in anterior uvea than aqueous
Where are topical ocular drugs metabolised?
In corneal epithelium
Or target tissue
Systemic ocular drugs are better for when trying to target what segment of the eye? What are the other advantages?
Posterior
Easier administration?
What is the blood ocular barrier (BOB)? What does it consist of?
Barrier between eye and blood stream
BAB - blood:aqueous barrier
BRB - blood:retinal barrier
The BOB affects the ability of many drugs to penetrate the eye. Which section of the BOB (BRB or BAB) sis leakier?
Blood:aqueous barrier leakier - allows agents to easily cross into anterior segment
Do lipophilic or hydrophilic drugs penetrate the BOB easier?
Lipophilic
What is the word for pupil dilation? What about constriction?
Mydriasis - relaxation
Miosis - constrinction
What type of drugs cause pupil dilation? (mydriasis)
Parasympatholytics - release iris sphincter
Sympathomimetics - contract the dilator muscle
Why may you want to cause pupil dilation? (mydriasis)
Eye exam
Contract ciliary body muscles to relieve painful spasms
What is the word for relaxation/paralysis of the ciliary muscle?
Cycloplegia
What innervates the pupil dilator muscle?
Sympathetic innervation
Nasociliary nerve
What innervates the pupil constrictor muscle?
Parasympathetic innervation
Occulomotor nerve
What drugs can be used for pupil dilation?
Atropine
Tropicamide
Phenylnephrine
What are the disadvantages/advantages of atropine?
Slow onset
Long duration
Causes systemic antimuscarinic effects - problem in horse (Colic)
Atropine causes mydriasis. Is it a sympathomimetic or parasympatholytic?
Parasympatholytic
Tear film maintains the health and clarity of the cornea. What do conditions like dry eye require as part of their treatment? Give an example
Tear substitutes
Pilocarpine
How does pilocarpine work? When might it be given?
Actively increases tear production, parasympathomimetic
Dry eye, during GA to prevent eyes drying out
What are the 3 categories of tear substitutes?
Aqueous substitutes
Mucin layer mimics
Drugs that replace the lipid portion of the tear film
Why are aqueous substitutes of tear films limited?
Lost quickly from ocular surface
Need frequent application
What is glaucoma? What does it cause?
Oedema of eye
Intraocular pressure damages optic nerve - pain blindness, irreversible structural changes
What can cause an increased intraocular pressure (leading to glaucoma)?
Decreased aqueous outflow
Glaucoma drugs include emergency treatment and drugs for management. What is the first line of Tx for emergency intervention? Give an example
Osmotic diuretics
Mannitol
How do osmotic diuretics work to treat glaucoma? What do they rely on being intact? Why are they for short term, emergency use only?
Increase in blood tonicity causes water to be drawn out of aqueous and vitreous humor
Intact BOB
Cannot be long term –> hypovolaemia
What drugs can be used to maintain glaucoma treatment?
Carbonic anhydrase inhibitors
Prostaglandin analogues
Beta blockers
Parasympathomimetic drugs
How do carbonic anhydrase inhibitors work to treat glaucoma? Give an example
Carbonic anhydrase ataylses hydration of CO2 to HCO3 and H+. HCO3 draws water into aqueous
Inhibition of this - stops water being drawn into aqueous
Brinzolamide
How do prostaglandin analogues work to treat glaucoma? Give an example
Increase uveoscleral outflow of aqueous
Latanoprost
How do beta blockers work? Give an example of a topical agent used
Reduce aqueous formation
Betaxolol
How do parasympathomimetic drugs work to treat glaucoma? Give an example
Contract ciliary body and constrict pupil
Widens drainage angle - increases aqueous outflow
Pilocarpine
