pharmacology

Question 1

Topical anesthetics

Answer 1

mechanism: prevent nerve depolarization
indications: facilitate dx tests and therapeutics

proparacaine 0.5%-most commonly used in SAM

Question 2

Mydriatics

Answer 2

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

Question 3

choosing an antimicrbial

Answer 3

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

Question 4

abx indications

Answer 4

topically applied

systemically administered

Question 5

antiviral medications

Answer 5

tx of feline herpesvirus

inhibits DNA synthesis

virostatic-Frequent administration

more toxic than abx

Question 6

Antifungal meds

Answer 6

indication: keratomycosis, systemic mycosis

disruption of cell membrane

expensive

applied 3-4 times daily

Question 7

Topical NSAIDs

Answer 7

anterior uveitis

inhibition of COX-1 &/or COX-2

apply 1-4 times daily

caution: corneal ulceration, posterior uveitis

Question 8

topical corticosteroids

Answer 8

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

Question 9

carbonic anhydrase inhibitors

Answer 9

treatment of glaucomatous eye

delay glaucoma in fellow eye

inhibition of aqueous humor pdn

caution: metabolic acidosis, GI disturbances, cats, topical drugs preferred

Question 10

Beta blockers

Answer 10

delay glaucoma in fellow eye, augment dorzolamide in glaucomatous eye

inhibition of aqueous humor pdc

caution: systemic beta blockade

apply SID BID

Question 11

prostaglandin analogues

Answer 11

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

Question 12

cyclosporine A

Answer 12

KCS, keratoconjunctivitis

inhibition of T cells, direct stimulation of lacrimal gland

apply BID

Question 13

Tacrolimus

Answer 13

KCS, other keratoconjunctivitis unresponsive to cyclosporine therapy

inhibition of T cells, direct stimulation of lacrimal gland

BID

FDA advisory

Question 14

Artificial tears

Answer 14

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

Question 15

issues with opthalmic drug delivery

Answer 15

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

Question 16

reasons for topical administration

Answer 16

minimize systemic drug dosing

achieves therapeutic drug levels for the ocular surface

simplicity of administration

Question 17

Effectiveness of ocular therapy depends on

Answer 17

drug potency

pharmacokinetic properties-lipid and aqueous solubility

ocular characteristics-blinking, lacrimation and tear drainage, corneal epithelial health, ocular inflammation, blood-ocular barriers

Question 18

fate of drugs delivered topically to the eye

Answer 18

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

Question 19

Nasolacrimal duct drainage

Answer 19

~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

Question 20

ocular surface penetration

Answer 20

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

Question 21

systemic absorption

Answer 21

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

Question 22

intraocular distribution

Answer 22

cornea–>aqueous humor–>anterior uvea–> lens–>vitreous humor

conjunctival/sclera–>anterior uvea

main drug clearance via aqueous outflow

Question 23

effect of pigmentation

Answer 23

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

Question 24

solutions

Answer 24

drug dissolved in solvent

mainly water-soluble drugs

relatively easy to apply

can be placed through a subpalpebral lavage system

Question 25

Suspension

Answer 25

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

Question 26

subpalebral lavage system

Answer 26

improves ease and safety of medication delivery to horses

allows frequent application of meds to the eyes

avoid eyelid manipulation

Question 27

viscous eye drops and gels

Answer 27

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

Question 28

ointment

Answer 28

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

Question 29

preservatives

Answer 29

inhibits microbial growth

in all multidose preps

potentially harmful to the eye-corneal epithelial toxicity, hypersensitivity

Question 30

rules for topical administration

Answer 30

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

Question 31

systemic drugs

Answer 31

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>

Question 32

subconjunctival injectioin

Answer 32

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

Question 33

subconjunctival injection MOA

Answer 33

direct diffusion through cornea/sclera

highest efficacy if adminstered under Tenon’s capsule

regurgitation through conjunctival hole

absoprtion into conjunctival blood vessels

Question 34

intraocular injection

Answer 34

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