Ophthalmic Pharmacology Flashcards
(35 cards)
describe ocular barriers to drugs
- tear film: dilutes drugs
- cornea: hydrophobic epithelium, hydrophilic stroma
- blood eye barrier: prevents protein molecules from entering eye
describe route choice for ophtho drugs
- topical: ocular surface to posterior lens capsule; can reach high concentrations
-1 drop is already 2-3 times what the eye can effectively absorb = NEVER a reason to give 2 drops back to back!!! will actually reduce overall absorption of the drug bc pisses off eye more - systemic: lids, orbit, posterior segment, perforated globe
describe how drugs penetrate the cornea
must be both lipophilic and hydrophilic!! (chloramphenicol is great at this)
describe how the blood eye barrier affects drugs
systemic drugs enter via blood vessels of uvea but if hydrophilic will have poor penetration
describe the blood eye barrier as relates to treating uveitis
uveitis breaks down blood eye barrier making it easier for more drugs to cross
describe the posterior blood eye barrier
the choroid is well-vascularized and most infectious diseases affect the choroid so most systemic drugs work well
describe drug formulations
- solutions: most common
-usually water-soluble salts, sometimes oil based
-easily contaminated and usually preserved - suspensions: most steroids
-sterile particulate solid + sterile liquid since drug is insoluble
-shake well!! 20x or 15 seconds!!
-generics NOT always same as original
-failure to shake is a major cause of short term treatment failures - ointments: most are mineral oil/petroleum
-drug mixed into melted vehicle then cooled
-greasy, blur vision
-preservatives not required
-modern ointments DONT slow wound healing
where do topical drugs go?
- onto face: most of it
-normal tear volume is 7ul
-most drops are 35-50ul so one drop is more than enough!
-drops typically gone in 5 min - down naso-lacrimal duct: systemic absorption
-anything >7ul also goes out via NL duct - conjunctival absorption via blood vessels = also systemic
- goal is transcorneal absorption into aqueous humor but most doesn’t actually go this route
how do you administer eye drops?
- 1 drop only!
- wait 5 min between drops!!
what determines the frequency of topical meds?
- vehicle: ointments less frequent than solutions
- prophylactic versus treating established disease
- spacing: must leave 5 min between drops of solution and 30 min between drops of ointment
what makes drugs go bad?
- expiration date: label is for UNOPENED bottle properly stored; once break seal they only last for about a month
- light, heat, air exposure: DONT place in bathroom or kitchen window (light, temp, humidity vairy widely)
- bacteria, fungi
- improper application: touch eye, cap on table, dirty hands; ascending contamination
all above is why eye drops are in tiny little bottles
what are the 2 ways to dilate and eye and the 2 ways to constrict the eye?
dilation:
1. parasympatholytic (anticholinergic)
2. sympathomimetics
constriction:
1. parasympathomimetics (cholinergic)
2. sympatholytics
describe topical mydriatics that paralyze the sphincter muscle and passively dilate the eye (2) (LO)
anti rest and digest, anti SLUD, paralyze the sphincter muscle and passively dilate the eye
- 1% tropicamide
-short acting (1-2 hours) for eye exams
-no pain relief
-takes 20 min to fully dilate - atropine:
-long acting (hours to days)
-pain relief by paralyzing sphincter
-prevents posterior synechiae
-stabilizes blood aqueous barrier
-ointment to prevent drooling - very bitter
(ointment gone off market so put finger on NL duct while administering)
-can exacerbate low tear production
-can slow gut and cause colic and kill horse!! keep listening to gut sounds when using with a horse to ensure not slow down too much
describe sympathomimetic drugs to dilate the eye
phenylephrine 2.5% or 10%
- increase HR
- cause cause serious systemic effects
- activates dilator muscles
- typically a preop cataract drug or HORNERS diagnosis
- also creates local vasconstriction
when is the ONLY time you don’t want to dilate the eye?
if see glaucoma
describe topical anesthetics
- proparicaine HCL 05%, tetracaine
- refrigerate if won’t use in 1 month
- keep out of light! throw away if brown
- onset in seconds, peak in 5-10 min, lasts 30 min
- 1 drop every 1-3 min better than a flood
- canNOT be used as a therapy:
-dries eyes, causes ulceration, delays healing, up-regulates pain receptors
describe cholinergics
- increase outflow via TM
2, contracts longitudinal ciliary muscle - green means miotic!!
- use for dry eye and for glaucoma
describe topical antibiotics
- chloramphenicol 0.5% solution or 1% ointment
-for cat conjunctivitis (chlamydophila/mycoplasma)
-septic keratitis/conjunctivitis with cocci
-easily penetrates cornea
-formerly resistant organisms are becoming sensitive again - tetracyclines: cat conjunctivitis
-terramycin/oxytetracycline with polymyxin B - cefazolin 5.5% for gram + organisms
-1 gram vial cefazolin
-mix with 2.5 ml sterile water
-put in 15ml artificial tears - aminoglycosides: good for rods!
-neomycin/polymyxin B combinations: good first choise as a prophylactic drug
-bacitracin added to ointments, gramidicin to solutions
-gentamicin and tobramycin: not prophy but only if rods are seen on corneal scrapings or if sensitivity testing indicates - fluoroquinolones:
-2nd gen: cipro, levo
-1000x better against gram -, also aerobic gram +
-use in septic keratitis with rods, cat conjunctivitis
-not a first choice drug! some cocci are resistant
4th gen: retains gram - but even better gram + spectrum
-less likely to develop resistance and can kill non-replicating
-reserved for multi=drug resitant infections!!
describe antiproteases
for melting corneal ulcers
- autologous plasma/serum
-dispense in 1 or more red tops
-sterile, keep fridge, lasts 1 week
-1 drop topically every 1-4 hours - topical oxytet
- oral doxy
- acetylcysteine and EDTA
describe dosing tips for topical antibitoics
prophylactic: 2-3 times a day
septic conjunctivitis: 3-4 times a day
septic keratitis: every 1-2 hours
cytology guides initial choice:
-rods: ciprofloxacin, gentamicin, or tobramycin
-cocci: triple antibiotic or chloamphenicol
-both: cefazolin AND topical ciprofloxacin or tobramycin, possibly moxifloxacin (4th gen)
describe topical antifungals
- almost exclusively for equine corneal fungal infections
- ointments are easier; if liquid usually use lavage tube
describe xamples of topical antifungals
- natamycin 5% polyene
-only commercially available agent
-thick solution
-poor penetration through inact epithelium
-expensive!! - compounded meds:
-itraconazole ointment: good absorption even through intact epi, can’t use lavage tube
-miconazole 1% solution: in DMSO (wear gloves), can be topically irritating
-voriconazole: expensive but good activity against southern isolates - if cannot afford to compound miconazole, can use OTC vaginal cream but can be irritating
- oral fluconazole:
-aspergilla resistant
-does not penetrate intact epi without DMSO so usually oral (good penetration orally)
describe topical antivirals
- trifluridine: most effective, expensive, can be irritating
- idoxuridine- compounded
-1/2 as effective, cheaper
both have to be given every 2-4 hours
- cidofovir: 1/2 as effective, BID dosing
describe systemic antivirals
- L-lysine: 400-500mg/cat/day all at once or divided:
-arginine competitior decreased viral replication
-reduced recurrences, viral shedding, duration, severity
-best is used at the start of an outbreak and during stress - famcyclovir (famvir): 90mg/kg BID for 3 weeks
-overall safe but hold back in patients with kidney or liver disease
-reserve for refractory patients when topicals fail
