5. ophthalmic pharmacology

what parts of the eye can be targeted with topical treatment?

ocular surface to posterior lens capsule

• corneal disease, anterior uveittis (intraocular inflammation)

what parts of the eye can be targeted with systemic treatment?

• lids, orbit, posterior segment, perforated globe

  • blepharitis (lid infection/inflammation), posterior uveitis, rupture

ocular barriers to drugs (4)

• tear film (topical)

  • dilutes

  • blinking — distributes tear film, removes drugs

• corneal epithelium — tight junctions (topical)

  • diffuse through cells (lipophilic); small molecules between cells

• stroma (topical)

  • high water content (hydrophilic)

  • drugs which penetrate the cornea must be lipophilic and hydrophilic

• blood:eye barrier

  • tight junctions in blood vessels of uvea, retinal pigmented epithelium, retinal blood vessels

  • keeps media clear

types of topical drugs

• solutions — most common

  • shortest duration

  • water-soluble; drugs completely dissolved in solvent

• suspensions — most steroids

  • particles of active ingredient + saturated aqueous vehicle → must be shaken prior to use

• ointments — most are mineral oil/petrolatum

  • longest duration

  • drug mixed into melted vehicle, then cooled

  • greasy; blur vision

how are topical broad spectrum antibiotics used to treat corneal lesions?

• prophylactic treatment of non-infected superficial epithelial loss

• more frequent application if infected

how do most antiviral drugs inhibit viruses?

• most are nucleoside analogues

• substitute for nucleotides in DNA synthesis → interfere with DNA polymerase & replication

• most don’t kill virus

which oral antiviral drug is safe to use in cats?

famciclovir

(others → bone marrow & kidney toxicity)

which anti-fungal class is most effective against equine isolates?

azoles

what type of drugs is most commonly used to treat KCS (dry eye)? what are their effects?

calcineurin inhibitors

• decrease T lymphocyte activation

• direct lacrimogenic effect — increase tear production

primary vs. secondary glaucoma

• primary: problem only with drainage

• secondary: drainage problem caused by something else (inflammation, lens out of position, etc)

how do prostaglandin derivatives help with glaucoma? how are they used?

• increase aqueous outflow, may decrease production

• only useful in dogs; only for primary glaucoma

• side effects: uveitis; may add topical steroid

how do carbonic anhydrase inhibitors help with glaucoma?

• decrease aqueous production

• use in both primary & secondary glaucoma

how do topical beta blockers help with glaucoma? what are potential adverse effects

• decrease aqueous production

• may increase outflow (miosis)

• primary or secondary glaucoma; prophylaxis

• some may worsen asthma (cats); bradycardia; decreased tear production

topical corticosteroids are typically used to treat what? when are they contraindicated?

• typically used to treat anterior uveitis (inflammation of front part of eye)

  • corneal penetration is essential

• contraindicated if corneal ulcer present

which topical corticosteroids have the best corneal penetration?

acetates (susp.) > alcohols (susp.) >> phosphates (solution)

• prednisolone acetate

• dexamethasone alcohol

topical NSAIDs are used to treat what? what are potential drawbacks?

• used for uveitis

  • good corneal penetration, some intraocular penetration

• may potential bacterial infection, corneal melting (don’t use if corneal ulcer present)

• caution: hyphema

ocular effects of atropine

• parasympatholytic; long acting (hrs — days)

• paralyzes ciliary body

• pain relief — ciliary body spasm in uveitis

• stabilizes blood:aqueous barrier

effects & uses of proparacaine HCl 0.5% / tetracaine (equine)

• topical anesthetic — not analgesic

• facilitates taking samples, measuring intraocular pressure

• epitheliotoxic, drying, delays wound healing

  • cannot use for pain relief

effects & uses of tropicamide 1%

parasympatholytic (paralyzes pupillary sphincter muscle) — dilator

• similar to atropine but shorter acting (~1-2 hr)

• used for retinal exams