pharmacology Flashcards
Topical anesthetics
mechanism: prevent nerve depolarization
indications: facilitate dx tests and therapeutics
proparacaine 0.5%-most commonly used in SAM
Mydriatics
mechanisms: cholinergic blockade
indications: visualization for opthalmic exam & intraocular sx, tx of anterior uveitis
common drugs: tropicamide, atropine
atropine better for pain
tropicamide-quicker
CI: Glaucoma, lens luxation, hypersalivation, decreased gut motility, lowered tear pdn
choosing an antimicrbial
site of infection
ability of drug to reach site of infection
type of organism
organism antimicrobial susceptibility
pharmacokinetics of selected drugs
potential adverse effects of meds
cost/compliance
abx indications
topically applied
systemically administered
antiviral medications
tx of feline herpesvirus
inhibits DNA synthesis
virostatic-Frequent administration
more toxic than abx
Antifungal meds
indication: keratomycosis, systemic mycosis
disruption of cell membrane
expensive
applied 3-4 times daily
Topical NSAIDs
anterior uveitis
inhibition of COX-1 &/or COX-2
apply 1-4 times daily
caution: corneal ulceration, posterior uveitis
topical corticosteroids
blepharitis, nonulcerative keratoconjunctivitis, anterior uveitis
inhibit pdn of arachadonic acid and infl cascade
apply 1-4 x daily
caution: do not use if corneal ulceration present, posterior uveitis, insulin resistance, hyperadrenocorticism, corneal deposits
carbonic anhydrase inhibitors
treatment of glaucomatous eye
delay glaucoma in fellow eye
inhibition of aqueous humor pdn
caution: metabolic acidosis, GI disturbances, cats, topical drugs preferred
Beta blockers
delay glaucoma in fellow eye, augment dorzolamide in glaucomatous eye
inhibition of aqueous humor pdc
caution: systemic beta blockade
apply SID BID
prostaglandin analogues
increase uveoscleral outflow, decrease aqueous pdn
emergency tx of glaucoma, ongoing tx of glaucoma
caution-miosis, uveitis, lens luxation, ineffective cats, side effects in horses
SID
cyclosporine A
KCS, keratoconjunctivitis
inhibition of T cells, direct stimulation of lacrimal gland
apply BID
Tacrolimus
KCS, other keratoconjunctivitis unresponsive to cyclosporine therapy
inhibition of T cells, direct stimulation of lacrimal gland
BID
FDA advisory
Artificial tears
physical wetting of the ocular surface, increased tear film stability
KCS, qualitative tear film d/o, exposure keratitis, keratoconjunctivitis, perioperatively
caution: preservative free formulations recommended if frequent applilcation or if other drugs also being administered
issues with opthalmic drug delivery
intact corneal epithelium and sclera are barriers to drug penetration
blood ocular barriers limit intraocular drug penetration
maximal drug action within the eye while limiting systemic absorption is desired
reasons for topical administration
minimize systemic drug dosing
achieves therapeutic drug levels for the ocular surface
simplicity of administration
Effectiveness of ocular therapy depends on
drug potency
pharmacokinetic properties-lipid and aqueous solubility
ocular characteristics-blinking, lacrimation and tear drainage, corneal epithelial health, ocular inflammation, blood-ocular barriers
fate of drugs delivered topically to the eye
loss through nasolacrimal duct
penetrates into eye through cornea and conjunctiva/sclera
absorbed into systemic circulation via conjunctiva/episclera and nasopharynx
between 1-10% of dose enters anterior chamber
Nasolacrimal duct drainage
~80% of applied drop exits NLD within 15-30 s
complete washout of applied drop within 10 min
influencing factors: size of drop, blink rate, lacrimation
ocular surface penetration
cornea-epithelium most significant barrier, transcellular and paracellular routes, effective penetration req solubility in oil and water, local infl, integrity of corneal epithelium
conjunctiva/sclera-mainly very hydrophilic, more permeable, conjunctiva–>sclera and scleral vessels
systemic absorption
transmucosal absoprtion in nasopharnyx, absorption into conjunctival and episcleral vessels
bypasses liver metabolism
can be dec by limiting NLD drainage and/or increasing ocular penetration
intraocular distribution
cornea–>aqueous humor–>anterior uvea–> lens–>vitreous humor
conjunctival/sclera–>anterior uvea
main drug clearance via aqueous outflow
effect of pigmentation
melanin preferentially binds drug
less free drug to reach target sites and less therapeutic effect due to initial drug loss to melanotic tissue
as drug builds up, melanin becomes drug reservior
slow release of drug and prolonged duration of action
solutions
drug dissolved in solvent
mainly water-soluble drugs
relatively easy to apply
can be placed through a subpalpebral lavage system
higher MW can impede drug crossing
protein binding can affect drug crossing
breakdown of blood ocular barrier allows more drug to cross
