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S&S > Ocular Pharmacology > Flashcards

Ocular Pharmacology Flashcards

1
Q

Main pharmacokinetic parameter for ocular drugs

A

Absorption

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2
Q

Important characteristics for topical abx?

A

Hydrophilic enough to stay in corneal stroma, but lipophilic enough to cross corneal epithelium

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3
Q

What prevents systemic drugs from getting into the eye?

A

Blood-aqueous and blood-retinal barriers

tight junctions, p-glycoprotein efflux pumps, NON-fenestrated capillaries (Fenestrated capillaries are capillaries that have tiny openings, or pores)

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4
Q

Requirements for systemic ocular drugs

A
Administered IV > IM; PO if high absorption rate
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5
Q

Requirements for topical ocular drugs?

A
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6
Q

Will systemically administered ocular drugs match in concentration once in the eye?

A

NO -> Drugs in the eye will always be a fraction of the concentration in the bloodstream

Like in BBB, inflammation increases concentrations

Similar to drugs getting across BBB

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7
Q

Pharacokinetics of ocular drugs:
- Drug Distribution
- Drug Metabolism
- Drug Elimination

A
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8
Q

What lesion locations in the eye may systemic administration be useful for?

A

Anterior segment (cornea, iris, lens); corneal stroma

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9
Q

Ocular lesions where systemic administration is not preferred // where topical is better

A

Corneal surface & conjunctiva

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10
Q

Which ABX are hydrophilic // NOT used in systemic administration?

A

Beta-lactams (ampicillin + sulbactam), aminoglycosides (gentamicin, tobramycin, amikacin)

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11
Q

Which systemic ABX are lipophilic?

A

Tetracyclines (doxy), Fluoroquinolones (enro), Macrolides (the -mycins -> erythro, clarithro, azithro-)

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12
Q

Systemic anti-fungals

A

Fluconazole, Voriconazole

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13
Q

When is topical administration not preferred?

A

For posterior segment disease

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14
Q

Topical administration can be enhanced by what method? Why is this “best”? What limits this method?

A

Increasing dose frequency – increases absorption and efficacy
- drug accumulates in eye over time -> results in highest concentration
- OWNER COMPLIANCE - difficult for owners to adminsiter so frequently (Q2 hours) + life-long ABX course

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15
Q

How come increasing topical drug concentration is limited in increasing efficacy?

A

Will only increase absoprtion in cornea up to a certain dose b/c of limited/small surface area of the cornea

Not enough surface area for all the drug to enter - maxes out

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16
Q

Method to increase topical drug absorption across the cornea without adjusting dosage?

A

DECREASE corneal thickness (gently scrape off diseased layers of cornea)

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17
Q

Topical Antibiotics

Polymyxin B
- beneficial actions & effects
- use / main species
- precautions

A
  • Cell wall inhibitor
  • Spectrum = Gram Negative
  • Low doses – used for endotoxemia in horses (bactericidal drugs -> dead bacteria release endotoxins into bloodstream)
  • Dose-dependent nephrotoxicity
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18
Q

Topical Antibiotics

Bacitracin
- beneficial actions & effects
- precautions

A
  • Cell-wall & peptidoglycan-synthesis inhibitor
  • Gram positive * Gram negatives
  • nephrotoxicity prevents parenteral use
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19
Q

Why is corticosteroid use contrainidicated in corneal ulcerations?

A

Can potentiate corneal ulcer infections + cause other severe ocular infections

ALWAYS READ THE LABEL!

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20
Q

What is the only FDA-approved anti-fungal ophthalmic drug? Its spectrum? Indications?

A

Natamycin
- similar to Amphotericin B
- binds to ergosterol in fungi cell membrane => oxidative damage and cell death
- filamentous fungi! -> aspergillus, fusarium
- DOES NOT PENETRATE THE INTACT CORNEA

NATAMYCIN corneal fungal infection, VORICONAZOLE stromal/deeper

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21
Q

What antibiotics does Natamycin have a synergistic effect with?

A

Tobramycin and Cefazolin (Aminoglycoside & Cephalosporin)

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22
Q

Trifluridine and Idoxuridine

Use, species, effect on viruses

A

Herpesvirus keratitis
- cats, horses
- are virostatic -> no effect on latent viral particles

(Idoxuridine = nucleoside analogue -> gets replicated into virus DNA, but then blocks BPing)

23
Q

What are the 3 main categories of anti-inflammatory ocular drugs?

A

Glucocorticoids, NSAIDs, Immunomodulators

24
Q

MoA of topical glucocorticoids

A

transactivation of anti-inflamm. genes & transrepression of pro-inflamm. genes –> block arachidonic acid pathway (phospholipase A2)

25
Q

When is topical glucocorticoid use contrainidicated?

Use is only indicated for anterior segment inflammation, conjunctivitis, keratitis, anterior uveitis

A

Presence of corneal ulcers

26
Q

Topical prednisolone acetate (1%) - benefits of acetate

A

Acetate increases lipophilicity of the drug = increases ocluar pentration, and increases potency (increases affinity for receptor)

27
Q

When is the use of Prednisolone Sodium Succinate or Phosphate indicated?

A

for superficial corneal diseases (b/c does NOT cross an intact cornea!)

28
Q

Dexamethasone sodium phosphate (0.1%) - benefits / indications?

A

Higher potency than topical prednisolone acetate (0.1% vs 1.0%)
- Penetrates an intact cornea
- available in formulations combined with antimicrobials (e.g., Neo/poly/dex)

29
Q

Why is hydrocortisone not preferred? When are they used?

A

Less potent / do not penetrate an intact cornea. Typically combined with ABX formulation.

30
Q

Adverse effects of topical glucocorticoids in the eye? (4)

A
  • potentiate infection (Fungus!!!)
  • Delay re-epithelialization of corneal ulcers
  • Calcific band keratopathy (chronic use)
  • Long-term use associated with development of endocrine issues

Calcific band keratopathy:
Band keratopathy is defined as a disease process that occurs from sub-epithelial calcium hydroxyapatite deposition leading to an opaque, band-like horizontal plaque across the cornea. This opacity often impacts the visual axis leading to decreased visual acuity in patients.

31
Q

Are topical ocular NSAIDs selective or non-selective?

A

Non-selective – inhibit BOTH COX-1 & COX-2

32
Q

Adverse effects of topical NSAIDs (3)

A
  • less concern for potentiating infection compared to topical GCs
  • decreased corneal epithelialization, ulcer/wound healing (thimersol)
  • no repported GI or renal effects (compared to systemic NSAIDs)

Ketorolac (0.5%), Diclofenac sodium (0.1%)

Thimersol-containing topical NSAID: Flurbiprofen (0.03%)

33
Q

WHEN are systemic GCs and NSAIDs used for ocular disease? WHY are systemic NSAIDs used more frequently than systemic GCs?

A

Indication: when inflammation cannot get under control using topical
- systemic NSAIDs used more frequently (topical GC + systemic NSAID) b/c non-selective drugs are more effective in getting inflammation under control

Flunixin meglumine > firocoxib in the horse

34
Q

Immunomodulator

Cyclosporine A
- MoA
- Indications

A
  • Binds calcineurin -> blocks IL-2 production & prevents T-cell activation
  • Most effective in ocular diseases mediated by lymphocytes (anterior uveitis)
  • Topical: surface ocular diseases since it does NOT penetrate intact cornea (immune-mediated keratitis; eosinophilic keratitis)
  • Systemic = $$$

T cells (also called T lymphocytes) are major components of the adaptive immune system. Their roles include directly killing infected host cells, activating other immune cells, producing cytokines and regulating the immune response.

35
Q

What is a suprachoroidal implant used for?

A

Anterior Uveitis (iris +/- ciliary body)
- delivers cyclosporine A for months-to-years

36
Q

Which autonomic nervous system has adrenergic vs cholienrgic receoptors?

A

Sympathetic: adrenergic (Alpha-1, Alpha-2, Beta-1, Beta-2)

Parasympathetic: cholinergic (Nicotinic & Muscarinic)

37
Q

Phenylephrine
- indications

A

Sympathomimetic
- causes mydriasis -> It is used before eye examinations, before and after eye surgery, and to treat certain eye conditions.
- dogs
- can be cobined with anti-cholinergic drugs to maximize dilation

38
Q

Tropicamide
- indications

A

Parasympatholytic
- prevents miosis
- short-acting
- more appropriate to use when diagnosing rather than for treatment!

39
Q

Atropine
- indications

A

Parasympatholytic
- prevents miosis
- long-acting! (especially in blue eyes — 14 days!)
- used for treatment; relieves pain from pupil constriction (ciliary spasm)
- can prevent synechiae (pupil stuck in one position) and 2º glaucoma

Synechiae
40
Q

Adverse effects of Atropine

A

decreased tear production –> KCS risk if tear production is not monitored (atropine antagonizes muscarinic receptor of lacrimal gland)

decreased GI motility (concern for colic in horses?)

Horses: Give q6 -> q12 -> q24 -> q48 -> PRN –> colic unlikely to occur 2º to atropine

41
Q

MoA of parasympathomimetics?

A

Cholinergic agonists (direct or indirect)

42
Q

Indications / adverse effects for parasympathomimetics?

A
  • not many b/c of adverse effects (v+, d+, anorexia, lethargy, weakness)
  • dry eye in dogs
  • somestimes glaucoma (not in horses as it’s been found to actually increase IOP)
43
Q

Timolol
- MoA
- Indications
- Precautions
- Species

A

Sympatholytic -> non-selective beta-blocker
-reduces IOP via decreasing aqueous humor production
- Precautions = Pts with cardiovascular disease (bradycardia, hypotension)
- Horses: better efficacy & fewer adverse effects (vs. dogs & cats)

44
Q

Dorzolamide is a carbonic anhydrase inhibitor. - MoA?
- Indications?
- How is it adminsitered?

A

In the eyes, carbonic anhydrase inhibitors reduce the production of aqueous humor by the epithelium of the ciliary body by reducing the production of bicarbonate ions and presumably reducing fluid flow.

  • treatment of glaucoma
  • combined with beta-blockers (-olol) since not very effective alone

Carbonic anhydrase is an enzyme that assists rapid inter-conversion of CO2 and H2O => H2CO3, H+ and HCO3-

45
Q

Prostaglandin analogues
- MoA?
- Indications?

A

Latanoprost -> GLAUCOMA TX
- LOWERs IOP via increased AH outflow (increases sclera permeability)
- DOGS and HORSES

46
Q

MoA of topical / local anesthetics for corneal and conjunctival surfaces?

A

sodium channel blockers
- block depolarization of nerves // propagation of nerve signals

47
Q

Indications for topical / local ocular anesthetics?

A
  • Diagnostic procedures (culture, tonometry)
  • Surgical procedures (analgesic – sole or adjunctive)
48
Q

When are topical ocular anesthetics contraindicated?

A

as therapy for ulcerative keratitis!!

can also be toxic to epithelium, can destabilize tear film, inhibit normal corneal blink reflex

49
Q

Most common topical ocular anesthetic used in clinical practice?

A

Proparacaine (effective within 1 minute; lasts 25-45 mins)

50
Q

Use of local administration of anesthetics (e.g., lidocaine, bupivicaine)?

Lidocaine: rapid onset, shorter duration (45-60 mins)
Bupivicaine: longer duration (5-10 hrs)

A

Blockade of sensory & motor innervation (surgical and non-surgical procedures)

51
Q

Topical Antiproteases
- Indications
- Topical vs Systemic

A

Prevent “corneal melting” in infectious-caused corneal issues by inhibitng matrix metalloproteinases (MMPs)

Topical: autologous serum, N-acetylsysteine
Systemic: tetracyclines, doxycycline in tears

Deep and melting ulcers are usually associated with Pseudomonas spp or beta-hemolytic streptococci. Proteases, hydrolases, and collagenases produced by bacteria, neutrophils, epithelial cells, dying keratocytes, and macrophages cause rapid COLLAGENOLYSIS and melting of stroma that can rapidly progress to a descemetocoele and possible corneal perforation within 24 hours. Topical (EDTA) (drops and ointment), N-acetylcysteine, and tetracyclines (oxytetracycline and doxycycline) inhibit MMPs via chlelating calcium and zinc. Undiluted topical autologous and homogenous serum or plasma has alpha 2-macroglobulin and alpha-1 proteinase inhibitor that act to inhibit MMP and serine protease. Frozen serum or plasma retain anti-protease efficacy for up to 180 days. Antiprotease drops should be applied 2–4 hours initially to inhibit melting and then can be decreased to every 4–6 hours. Oral doxycycline (10 mg/kg every 24 hours) is also effective as an antiproteolytic agent and can be combined with topical antiprotease drops.

52
Q

How is autologous serum collected for use as a topical antiprotease?

A

Collected aseptically // maintained sterility

53
Q

Why don’t systemic anti-viral drugs work

A

Too hydrophilic (can’t stay in corneal stroma)

S&S (53 decks)

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