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
Suspension
drug particle suspended in aqueous vehicle
drugs with low aqueous solublity-corticosteroids
relatively easy to apply
can be placed through subpulpebral lavage system
potential for irritation, incorrect dosing
subpalebral lavage system
improves ease and safety of medication delivery to horses
allows frequent application of meds to the eyes
avoid eyelid manipulation
viscous eye drops and gels
aqueous solutions enhanced by polymers, gums
enhanced drug penetration, drug retention vs solutions due to increased ocular residence time
can’t be administered through SPL
ointment
oil base
water soluble and lipid soluble meds suspended or dissolved in vehicle
prolonged ocular surface time
do not use with deep/full-thickness ulcers or if globe perforation is a concern
preservatives
inhibits microbial growth
in all multidose preps
potentially harmful to the eye-corneal epithelial toxicity, hypersensitivity
rules for topical administration
apply least viscous med before more viscous meds
wait min 5 mins between meds
use no more than 1 drop of solution/suspension or 1/4” strip of ointment per dose
systemic drugs
hydrophilic drugs<lipophilic></lipophilic>
<p>
higher MW can impede drug crossing</p>
<p>
protein binding can affect drug crossing</p>
<p>
breakdown of blood ocular barrier allows more drug to cross</p>
</lipophilic>
subconjunctival injectioin
delivers therapeutic levels of drug to the ocular surface and anterior segment
duration: water soluble: 8-12 hr, suspensions: 2-3 weeks
use when frequent dosing of eye drops is not possible, immediately post op
repeated injections will result in local infl rxn
subconjunctival injection MOA
direct diffusion through cornea/sclera
highest efficacy if adminstered under Tenon’s capsule
regurgitation through conjunctival hole
absoprtion into conjunctival blood vessels
intraocular injection
intracameral-anterior chamber, during sx, risk of corneal or uveal damage, lens perforation
intravitreous-indicated in vision/globe threatening posterior segment dz, risk of drug toxicity to retina, damage to lens and posterior segment
sterility crucial
general anes
referral
