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OPH > Module 3 > Flashcards

Module 3 Flashcards

1
Q

Principles of medicating the eye

A

Topical penetration - transcellular (relies on lipophilic-hydrophilic balance and small 0.6-3nm) or paracellular.
Corneal epithelium: lipophilic, stroma: hydrophilic, endothelium: lipophilic.
Drugs with lipophilic and hydrophilic properties cross the cornea best; aka oil/water coefficient, optimum o/w for corneal penetration is 10:1 to 1000:1.
For surface disease these obstacles are not important
Improved penetration has been achieved by combining with organic salts or preservatives (cell morphological changes can occur).
Unpreserved drops - fridge at 2-8C and discarded after 7 days.
Weak bases or acids, non-ionised (base HA) and ionised (cation/anion H+/A-). Equilibrium depends on dissociation coefficient (pKa) and solvent pH, thus altering pH can alter permeability.
Need to be non-irritant - compliance etc impact but also inflammation causes increased tear osmolarity (proteins) which bind drug.
pH 4.5 - 9 to be comfortable

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2
Q

Cont….

A

Suspensions - particles must be <10um in size. Advantage of particle retention on the surface increases drug concentration.
Ointments retained for extended periods - 0.5% clearance/minute
Tear film - estimated 7-10ul, turnover 1ul/min. Avg eye drop 40ul, palpebral fissure holds 25-30ul, NL drainage results in some systemic absorption. Ideally drop size would be 5-15ul, advised to wait 10 mins between applications.
Penetration across conjunctiva, 2-30x more penetrable than the cornea, paracellular. Polar/non-polar not a vast difference.
Scleral permeability 10x cornea. Size of drug more important for permeability.
Contact lens/collagen shields soaked in drugs increase penetration through increase contact time, dependent on length of soak and properties of drug and lens. Release is rapid and poorly controlled.
Lower conjunctival inserts.
Subconjunctival injections - absorbed across episclera and sclera via limbus, and leak onto conjunctival and corneal surface. Last 8-12hours for solutions, suspensions last extended periods up to 3 weeks. Care however if ulcer could appear during this time.

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3
Q

Cont….

A

Intracameral - injection into chamber, caution - toxicity, preservative free, suitable pH and osmolarity must be considered. e.g. plasminogen activating factor (25ug) for fibrinolysis, cefuroxime for bacterial endophthalmitis.
Posterior segment disease - not well served by topical medications, systemic meds required. e.g. steroid inj (trimcinolone), and gentamicin. Gentamicin is used for cyclodestruction, retinotoxic, so used in non-visual end stage eyes. Associated with intraocular sarcoma in cats so not an option for them.
Sustained release implants - e.g. cyclosporine.
Systemic medication penetration depends on blood ocular barriers, lipophilicity of drug, molecular weight. High lipid solubility increases penetration. Doxycycline, trimethoprim and chloramphenicol are good.

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4
Q

Antimicrobials

A

Targets of action:
1 - cell wall - penicillin and cephalosporins
2 - cell membrane - polymyxin b
3 - bacterial protein synthesis (ribosomes) - tetracycline, chloramphenicol, aminoglycosides
4 - bacterial folate synthesis - sulphonamides
5 - Bacterial DNA synthesis - quinolones

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5
Q

Bactericidal

A 
Aminoglycosides
Bacitracin
Cephalosporins
Fluoroquinolones
Gramcidin
Penicillins
Polymyxin B
Vancomycin
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6
Q

Bacteriostatic

A 
Chloramphenicol
Macrolides & Lincosamides; Clindamycin and eythromycin
Sulphonamides
Trimethoprim
Tetracycline
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7
Q

Penicillin

A

CIDAL
gram +ve
inhibit cell wall synthesis
B-lactam ring (bacteria resistance if produce b-lactamase)
combo with a lactamase inhibitor e.g. clavulanic acid or sulbactam)
Transpeptidase modification –> MRSA –> resistant to all penicillins and cephs.
Poor ocular penetration unless inflamed
Carbencillin, piperacillin, ticarcillin - gram -ve activity including pseudomonas

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8
Q

Cephalosporins

A

As for penicillins
FOUR generations according to side chain
First gen: cephalexin and cefazolin, gram +ve activity
Second gen: cefuroxime, gram +ve and some gram -ve activity
Third gen: ceftiofur, ceftazidime, gram +ve and more gram -ve activity (intravitreal injections used in people with endophthalmitis)
Fourth gen: cefepime, broad gram +ve and gram -ve activity including pseudomonas.

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9
Q

Bacitracin

A

CIDAL
gram +ve activity - cell wall synthesis interference
Little to no corneal penetration
Unstable in solution
Seen in triple ointments with neomycin and polymixin B

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10
Q

Vancomycin

A

CIDAL
gram +ve, effective against MRSA
resistance developing so shouldn’t use
Used for human endophthalmitis and MRSA keratitis

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11
Q

Polymixin B

A

CIDAL
Cell wall membrane
Gram -ve including pseudomonas
poor corneal penetration

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12
Q

Gramicidin

A

CIDAL
toxic systemically - haemolytic anaemia
Cell membrane target

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13
Q

Aminoglycosides

A

CIDAL
inhibit protein synthesis
parenteral or topical, poor oral absorption
gram -ve bacteria, little gram +ve (s. aureus excluding MRSA)
Synergistic to B-lactams but shouldn’t be mixed in same vial/formula
Neomycin, gentamicin, tobramycin, amikacin
Limited corneal penetration unless inflammation, deleterious to corneal wound healing.
Not for use intracamerally - endothelial toxicity.
Intravitreal injections of gent for chemical cycloablation . Amikacin, least retinotoxic and used intravitreally in people for endophthalmitis.

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14
Q

Fluoroquinolones

A

CIDAL
Four generations, newer generations have better gram +ve activity
2nd gen: enrofloxacin, ciprofloxacin, ofloxacin - activity against Pseudomonas species but resistance is developing, little gram +ve activity. Ofloxacin has some aqueous penetration. Enrofloxacin –> retinal degeneration in some cats.
3rd gen: marbofloxacin - non-toxic 20x recommended dose
4th gen: gatifloxacin, moxifloxacin, besifloxacin - gram +ve activity. Moxifloxacin - good corneal and intraocular penetration.
Drug safety - muscle pain, tendonitis, tendon rupture, joint pain - continue after finishing meds

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15
Q

Tetracyclines

A

STATIC. Broad spectrum. Efflux activity in bacteria –> resistance
Useful for Rickettsial infestions, Borrelia, Mycoplasma, Chlamydophila, Moxella. Acts on 50s. Also MMP inhibition, anti-apoptotic and anti-inflammatory. Should not be given with food containing iron, calcium or magnesium as reduces absorption except doxy. Discoloured teeth in young animals.
Doxycycline - most effective MMP-inhibitor, reaches tear PO. Should have food to avoid oesophageal strictures.

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16
Q

Macrolides and Lincosamides

A

STATIC. Inhibit protein synthesis - 50s.
Gram -ve as well as mycoplasma, chlamydophila, bartonella
Macrolides: Erythromycin, azithromycin (has been used for Bartonella infection in cats - resistance so doxy preferred), clarithromycin
Lincosamide: clindamycin - toxoplasma gondii infections

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17
Q

Chloramphenicol

A

STATIC. Acts on 50s. Broad spectrum of activity but Pseudomonas is resistance. Ricketssia, chlamydophila, mycoplasma
Systemic use is associated with haemopoietic disorders (BM suppression and fatal aplastic anaemia).
Ointment is reported to achieve higher concentration in cornea and aqueous.

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18
Q

Sulphonamides and trimethoprim

A

STATIC. Alter bacterial folate metabolism. Activity against gram +ve and some negative. Pseudomonas is resistant.
Trimethoprim-sulfadiazine therapeutic concentrations in aqueous and vitreous after oral administration.
KCS is an adverse effect - toxic lacrimal adenitis - 15-25% of cases.
Inactivated by purulent discharge

19
Q

Antifungals

A

Fungal keratitis reported but uncommon, more likely working dogs.
4 classes: polenes, pyrimidines, azoles, echocandins.
Most static rather than cidal and attack cell wall

20
Q

Amphotericin B

A

For Aspergillus, blastomyces, candida, coccidiodes, cryptococcus spp.
Orally poor bioavailability. Renal, hepatic and haematological SE IV, different formulations may reduce systemic SE.
Topical solution compounded with sterile water - refrigerated and kept away from light.
Poor penetration through intact epithelium.
Good for ulcerative fungal keratitis.

21
Q

Natamycin and Nystatin

A

Natamycin - Activity against filamentous fungi. Poor corneal penetration but good topically.

Nystatin - broad spectrum, local toxicity and limited penetration limits use

22
Q

Ketoconazole and miconazole

A

Imidazole anti-fungal agents.
miconazole - suspension and cream - therapeutic corneal and intraocular penetration
Ketoconazole - absorbed systemically, hepatotoxicity in some cases. cataractogensis.

23
Q

Fluconazole, itraconazole, voriconazole, posaconazole

A

Triazole anti-fungal.
Fluconazole - yeasts limited against against filamentous fungi, great absorption and uptake into the eye
itraconazole - broader spectrum with good oral absorption but poor ocular penetration
voriconazole - great spectrum, good bioavailability, tear film and aqueous penetration. Cats - anorexia, neuro and azotaemia - not advised.

24
Q

Caspfungin and micafungin

A

Echinocandins
Fungicidal to Candida spp
Static to Aspergillus and other filamentous fungi
Intraocular penetration is poor

25
Q

Antivirals

A

Nucleoside analogues = virostatic, target viral replication within host cell
Idoxuridine and trifluorothymidine - 4-6x topically, effective for FHV-1
Cidofovir - long intracellular half life = BID, NL duct stenosis in people
Aciclovir - poor for cats, system admin = BM probs, renal and hepatic dz
Ganciclovir - in vitro good for FHV-1
Peniclovir (metabolite of famciclovir) - good in vitro FHV-1, 90mg/kg suggests, 40mg/kg shown to work, but 125mg/cat often used

Interferons - involved in anti-viral defence, inhibit viral genome translation. Orally degraded in GI tract. Some in vivo studies show increased anti-viral cellular protein following topical administration.

L- lysine - postulated to reduce FHV-1 replacation by competing with L-arginine. Mixed results but largely fallen out of favour and waste of ££

26
Q

Anti-parasitics

A

Fenbendazole - 20mg/kg for 4 weeks, E. cuniculi in rabbits, some evidence recently suggesting E. cuniculi involvement in dog and cat cataracts
Angiostrongylus vasorum - microfilarial migration or coagulopathy - moxidectin or fenbdazole
Pentivalent antimonials (sodium stibogluconate +/or allopurinol) Leishmania infantum - can cause ocular disease as well as spectrum or other systemic diseases
Thelazia callipaeda and T. californiensis - conjunctivitis/dacrocystitis, imidaclopride, moxidectin

27
Q

Anti-inflammatories and immunosuppressant drugs

A

Phosphalidase catalyses phospholipid –> arachidonic acid
Arachidonic acid –> prostaglandins by (cyclooxygenase) COX 1 & COX 2
Arachidonic acid –> leukotrienes by LOX (lipoxygenase)
Inflammation = vasodilation, vascular permeability, exudation, chemotaxis, immune activation

28
Q

Corticosteroids

A

Inhibit phospholipase A2 and stabilise lysosomal membranes.
Anterior and surface disease may be managed topically, posterior disease requires intraocular injections or systemic therapy
Prednisolone acetate (lipophilic) penetrates well cf. penetrate sodium phosphate (hydryophilic) does not.
Dexamethasone sodium phosphate 10x more potent but doesn’t penetrate well
hydrocortisone - does not penetrate - only for surface use
Contraindicated in most ocular infections.
Increases lytic activity of collagenases - worsening melting.
Systemically - have little effect on corneal healing in the face of ulceration cf. topically
Associated with subcapsular cataracts in cats.
IOP increase may be seen due to increase in ECM products, seen in dogs with glaucoma and normal cats
systemic effects on HHA and iatrogenic HAC from chronic topicals
Calcific corneal degeneration topical use.

29
Q

NSAIDs

A

Anti-inflammatory, anti-pyretic, analgesic properties.
Inhibit cyclooxygenase (COX) pathway and production of PGs.
COX1 present in all tissue and important for homeostasis and gut protection, COX2 primarily in inflamed tissues (COX2 is POO)
SE: gut ulceration and renal dz, primarily due to inhibition of COX1
Non-selective: aspirin, diclofenac, indothemacin, ibuprofen, flurbiprofen, ketorolac
Selective: meloxicam, deracoxib, etodolac, carprofen,
COX pathway inhibition increases production of leukotrienes via LOX pathway. gastric leukotriene B4 (LTB4) causes chemotaxis and degranulation of neutrophils –> mucosal damage. Dual inhibitors may improve gut protection e.g. tepoxalin
Neovascularisation inhibitors, can be associated with local irritation and IOP increases. Caution with ulceration, definitely not in keratomalacia

30
Q

Immunosuppressants

A

High doses of corticosteroids
Azathioprine or cyclospirne - slower onset can be used as steroid sparing
Cytarabine IM optic neuritis - GME
Lomustine, leflunomide and mycophenolate have been used for GME and IMR with varying success
Cyclosporine (bind cytoplasmic receptor cytophilin), tacrolimus (binds FK-binding protein and inhibit calcineurin), pimecrolimus, rapamycin (binds FK-binding protein but not via calcineurin) - ALL inhibit T cell activation.
Systemic cyclosporine used for IM blepharitis, episcleritis and extraocular polymyositis, also uveitis.
Aziothioprine - IM optic neuritis, GME, uveodermatological syndrome, ligneous conjunctivitis (Dobies and GSD), liver dz - bloods pre and 2 weeks after starting meds.
Megoestrol acetate - eosinophilic keratoconjunctivitis refractory to CCS/cyclosporine, SE - neoplasia, pyo, DM, best avoided

31
Q

Anti-glaucoma - prostaglandin analogues

A

Prostaglandin analogues: PGF2a derivatives, act on F prostanoid receptors (absent in cats) and increase uveoscleral outflow. Pro-inflammatory. Caution in uveitis.
Latanoprost, travaprost, bimatoprost, tafluprost, used BID, peak effect 6 hours post application.
Hyperaemia common, miosis, contra-indicated in anterior lens-luxation, caution missing doses as rebound mydriasis is seen and precipitate anterior lens-luxation

32
Q

Carbonic anhydrase inhibitors

A

Limit production of bicarbonate ions in the non-pigmentated ciliary epithelium and therefore active secretion of Na and water movement
Dorzolamide - 5.6pH, reduces IOP in normal and glaucomatous dogs and cats, TID
Brinzolamide - 7.5pH (closer to physiological pH 7.4), ineffective in normal cats but does drop IOP in glaucomatous cats.

Systemic CAI - acetazolmide, methazolamide - SE, severe in cats so not recommended. Occ used in acute glaucoma cases (dogs)

33
Q

B-blockers

A

Block B-receptors on ciliary epithelium, inducing decrease in cAMP levels, reduction in secretory function (blocking NA/K ATP-ase pumps), modulation of ciliary blood flow.
Timolol 2-3 times daily - effective in glaucomatous dogs, modest effect in cats.
SE: bradycardia, hypotension, bronchoconstriction, miosis. Care in small pts.

34
Q

Cholinergic agonists

A

Pilocarpine (ocular irritation due to low pH) and carbachol (injected intracameral after phaco to avoid POH)
Increase conventional outflow.
Parasympathomimetics - miosis
Obsolete for glaucoma now

35
Q

Alpha-2 adrenergic agonists

A

Brimonidine and apraclonidine - reduce aqueous production.
Severe SE in cats - bradycardia, GI dz, hypersalivation.
Not used in our pts

36
Q

Osmotic diuretics

A

Emergency situations to lower IOP
IV mannitol over 30mins, onset of action 1 hour, last 24 hours.
Oral glycerol - onset 1 hour, lasts 10hours, contraindicated in DM

37
Q

Neuroprotection

A

In its infancy
Cell death –> glutamate release –> neighbouring cell death
N-methyl-D-asparate receptor antagonist - memantine trialled for preventing retinal ganglion cell loss in glaucoma - poor results
Amlodipine - Ca channel blocker, potentially neuroprotective

38
Q

Mydriatics

A

Dx, tx and to aid sx
Anti-cholinergics - tropicamide and atropine. Blocks cholinergic receptors in sphincter muscle.
-Tropicamide - 10-20 mins onset, lasts 6-8 hours, increase in IOP so caution in glaucoma. Reduces tear production in cats, not dogs
-Atropine - 40 mins onset, lasts 3-14 days, bitter –> hypersalivation, reduces tear so caution KCS
-Cyclpentolate - as for atropine but chemosis in dogs.

Sympathomimetics - phenylephrine or adrenaline, maximise dilation when used in conjunction with above.

  • phenylephrine causes conjunctival pallor, used to differentiate conjunctival hyperaemia and episcleral hyperaemia (takes longer 1-2 mins), also horner’s lesion localisation.
  • adrenaline - used intracamerally for intraocular surgery, poor penetration topically, must be preservative free.
39
Q

Local anaesthetics

A

for tests and examination/treatment
Block nerve depolarisation - inhibit Na influx
topicals:
-proxymetacaine; onset 1 min, last 45 mins, extended to 55 mins with second application in dogs. Cats, last 25mins.
-tetracaine; 1min onset, similar duration. Stings.

Regional blocks - auricopalpebral nerve block, retrobulbar block (care IV/intrathecal - cardiac arrest/brainstem anaesthesia).

  • lidocaine; rapid onset, lasts 45-60 mins
  • bupivacaine; last 5-10 hours, 4x more potent, onset less rapid so usually combined with lidocaine
  • intracameral lidocaine for phaco - 0.1ml!.
40
Q

Tear film replacement

A

Replacements: aqueous, substitutes, mucinomimetics, viscoelastics, lipid based substitutes.
Hypotonic or isotonic tears are advised due to hypertonicity of tears in KCS
Aqueous subs - methylcellulose, hydroxypropylmethylcellulose - short lasting but do not cause blurring
Autologous serum - improves impression cytology and clinical scores, used in people with KCS. TGF-B and EGF postulate to improve corneal healing with ulceration.
Viscous agents - carbomer polymer, last longer, mainstay of tear replacements
Sodium hyaluronate - high viscosity, greater retention times, pseudoplasticity, improved TBUT, benefits in corneal ulceration
Lanolin/paraffin-based - mimic lipid component, good retention, blurry vision, useful at night

41
Q

Tear stimulation

A

Cyclosporine - binds cytoplasmic receptor cytophilin, most successful when tear production >2mm/min as some functional lacrimal tissue remains
Tacrolimus - binds FK-binding protein, inhibit calcineurin blocking production of IL-2 and activation of T cells. prescribed via cascade to those not responsive to cyclosporine.
Topical pilocarpine used for neurogenic KCS, denervation phenomenon. 1 drop/10kg BID, increasing by 1 drop every 2-3 days until response. AE - V+/D+, urinary incontinence hypersalivation

42
Q

Anti-collagenases

A

MMPs and serine proteinases - responsible for normal corneal homeostasis, unbalanced in keratomalacia.
Acetylcysteine - speed health and anti-collagenase activity
Ethylenediaminetetraacetic acid (EDTA) chelates zinc and calcium
Doxycycline - MMP inhibitor, chelate cations, inhibit a-antitrypsin and chemotaxis.
Autologous serum - anti-collagenase activity, a-macroglobulins and a1-antitrysin. Epithelial growth factors. -4C for 1month, -20C for 3 months.

43
Q

fibrinolytics

A

Tissue plasminogen activator - lyse fibrin that may lead to synechiae, retinal traction, gonioimplant blockage etc. tPA is a serine protease converts plasminogen to plasmin in the presence of fibrin, fibrinolysis in <15 minutes. Indicated post op or post trauma IO fibrin. If risk of re-bleeding do not administer!! Intracameral injection. Topical insufficient concentration in aqueous to result in fibrinolysis

44
Q

anti-fibrotics

A

Advocated to prevent collagen deposition around glaucoma implant.
Mitomycin-C (MMC) derived from Streptomyces caespitosus. Topical use via a soaked sponge. Avoid contact with epithelial surface of conjunctiva.

5-fluorouracil (5-FU) - has been used in human and canine glaucoma surgeries, no controlled studies but appears less potent than mitomycin-c

OPH (13 decks)

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