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Drugs Used to Treat Conjunctivitis in Cats & Dogs

Renee Carter, DVM, DACVO, Louisiana State University

Ophthalmology

|August 2022

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conjunctival hyperemia and mucopurulent ocular discharge
FIGURE 1 Marked conjunctival hyperemia and mucopurulent ocular discharge in a dog with conjunctivitis. Image courtesy of Louisiana State University

Conjunctivitis is inflammation of the conjunctiva (ie, mobile mucous membrane that lines the eyelids [palpebral] and surface of the globe [bulbar]) and can be primary (eg, allergic disease, immune-mediated inflammation, infectious disease process) or secondary (eg, to adnexal disease, tear film disorders, intraocular disease, systemic disease process).1 Clinical signs include conjunctival redness (eg, hyperemia; Figure 1), swelling, ocular discharge, and discomfort (eg, squinting or rubbing of the affected eye). Ulceration is less common but can occur following viral insult or injury to the conjunctiva.1

Primary conjunctivitis should be differentiated from other ocular disorders with ocular redness (eg, episcleritis, keratitis, uveitis, glaucoma) that would require additional diagnostic investigation and different management strategies. Most causes of conjunctivitis in cats should be considered infectious until proven otherwise2; causes in dogs are commonly noninfectious.

Disorders

Allergic Conjunctivitis

The most common cause of bilateral conjunctivitis in dogs is allergic disease (Figure 2). Periocular redness and alopecia are typical in patients with allergic conjunctivitis secondary to type 1 hypersensitivity reactions (eg, atopy).3 Lymphocytes and plasma cells can often be seen on conjunctival cytology.

Follicular conjunctivitis with prominent lymphoid follicles involving the posterior aspect of the third eyelid in a dog with allergic conjunctivitis
Follicular conjunctivitis with prominent lymphoid follicles involving the posterior aspect of the third eyelid in a dog with allergic conjunctivitis
FIGURE 2 Follicular conjunctivitis with prominent lymphoid follicles involving the posterior aspect of the third eyelid in a dog with allergic conjunctivitis. Image courtesy of Louisiana State University
Acute, Bilateral Chemosis, & Blepharoedema

Acute, bilateral chemosis (Figure 3) and blepharoedema may be associated with an immediate-type hypersensitivity reaction mediated by histamine and immunoglobulin E.3 Reactions can be caused by contact allergy, vaccine reaction, or insect envenomation and should be treated with IM or IV short-acting corticosteroids and antihistamines, possibly in conjunction with topical corticosteroids.3 In patients with suspected ocular exposure to an irritating compound, the eye should be well irrigated with saline and stained with fluorescein; surface pH should also be monitored.

Extensive chemosis with significant swelling of the conjunctiva and relative lack of inflammation in the right eye of a dog following insect envenomation
Extensive chemosis with significant swelling of the conjunctiva and relative lack of inflammation in the right eye of a dog following insect envenomation
FIGURE 3 Extensive chemosis with significant swelling of the conjunctiva and relative lack of inflammation in the right eye of a dog following insect envenomation. Image courtesy of Louisiana State University
Eosinophilic Conjunctivitis
Nodular Granulomatous Episcleritis

Eosinophilic conjunctivitis is most common in cats. Feline herpesvirus (FHV)-1 may be an etiology for this disorder, but this has not been verified.2 Both the conjunctiva and cornea may be involved. Eosinophils and/or mast cells are present on conjunctival cytologic samples.

Primary inflammation of episclera (ie, connective tissue between the conjunctiva and sclera) is often immune-mediated, resulting in multiple fleshy pink to tan-colored nodules (Figure 4). Collies, cocker spaniels, and Shetland sheepdogs are overrepresented.4

Clinician's Brief
FIGURE 4 Focal nodular mass in a dog with nodular granulomatous episcleritis. Image courtesy of Louisiana State University

Drugs to Manage Conjunctival Inflammatory Disorders

The following medications control redness, discharge, pain, and inflammatory cell infiltrates that characterize conjunctivitis of any etiology. Topical treatment (ie, eye drops, ointment) is often sufficient for primary conjunctivitis because of disease distribution in the conjunctiva, ease of application, increased drug levels at the site of interest, and reduced risk for systemic adverse effects. 

Conjunctival inflammation is primarily managed with topical steroids or NSAIDs, depending on conjunctivitis etiology and severity. Secondary forms of treatment include topical antihistamines, mast cell stabilizers, and vasoconstricting agents. Topical management options are described here.

Corticosteroids
  • Neomycin/polymyxin/hydrocortisone (1% suspension or ointment)
  • Neomycin/polymyxin/dexamethasone (0.1% suspension or ointment)
  • Prednisolone acetate (1% suspension)
  • Prednisolone sodium phosphate (1% suspension) 

Topical corticosteroids affect the lipoxygenase and cyclooxygenase pathways (reducing inflammatory mediators [ie, reducing swelling, redness, and pain]), are commonly used to treat inflammatory ocular surface disorders, and can be used in cases of noninfectious conjunctivitis.5 

Dosage (Dogs, Cats)

  • One drop or one-quarter–inch strip ointment per affected eye
  • Frequency should be based on severity but is most commonly every 12 to 24 hours.

Key Points

  • Suspensions should be shaken well before application. 
  • Prolonged contact time with ointment can result in higher levels of local drug delivery compared with suspensions.5
  • Hydrocortisone is a weak corticosteroid appropriate for treating mild conjunctivitis.5
  • Treatment should be continued for 2 to 3 days beyond resolution of clinical signs.
  • As most cases of feline conjunctivitis are primarily infectious, use of topical corticosteroids is not recommended. 
  • Topical corticosteroids are contraindicated in patients with corneal ulceration and/or infectious conjunctivitis (cats). 
  • Neomycin can cause local drug-related hypersensitivity reactions that result in increased ocular redness, discomfort, and blepharitis.1 
  • Long-term use of topical corticosteroids can result in crystalline lipid corneal deposits.5
  • Topical corticosteroids can reduce the risk for adverse effects associated with systemic administration; however, systemic absorption can still occur with topical application.6
  • Anaphylaxis can occur rarely in cats following application of topical ocular medications; polymyxin B (in both triple antibiotic ointment and triple antibiotic with dexamethasone and polymyxin B sulfate with oxytetracycline hydrochloride) has been associated with anaphylaxis.7
  • Cats with eosinophilic conjunctivitis should initially be managed with topical prednisolone acetate products and monitored for corneal ulceration. 
    • Patients with eosinophilic conjunctivitis often require long-term therapy tapered to the lowest level that controls clinical signs.2 Topical or systemic antiviral therapy may be required, and patients should be monitored for corneal ulceration. Additional management options (eg, topical cyclosporine, compounded topical megestrol acetate) may be required for refractory cases.2,8
  • Topical steroids can be used for nodular granulomatous episcleritis; evaluation by an ophthalmologist is recommended.
Ophthalmic NSAIDs
  • Diclofenac (0.1% solution)
  • Ketorolac (0.4%-0.5% solution)
  • Suprofen (1% solution)
  • Flurbiprofen (0.03% solution)
  • Bromfenac (0.07%-0.09% solution)
  • Nepafenac (0.1%-0.3% suspension)

Topical NSAIDs can reduce ocular surface inflammation, swelling, and pain associated with conjunctivitis.5 Topical application can reduce the risk for systemic adverse effects associated with oral and injectable NSAID therapy.

Dosage (Dogs, Cats)

  • One drop per affected eye
  • Frequency should be based on severity but is most commonly every 12 to 24 hours.

Key Points

  • Topical ophthalmic NSAIDs are nonselective COX inhibitors.5
  • Frequently used in patients with mild to moderate ocular inflammation 
  • Local irritation may occur after topical application.
  • Caution should be used in patients with concurrent corneal ulceration, as NSAIDs may slow corneal epithelialization.9 Increased healing time in dogs with indolent corneal ulcers has been reported.10 
  • Effect of topical NSAIDs on corneal sensitivity has been evaluated,11,12 as reduced sensitivity would be expected to delay corneal wound healing. Corneal sensitivity was not reduced in healthy, nonbrachycephalic dogs given topical diclofenac and flurbiprofen or in normal, domestic shorthair cats given diclofenac, ketorolac, or flurbiprofen.11,12 
  • Caution should be used in patients with history of increased intraocular pressure, as a decrease in aqueous outflow has been reported; decrease in the efficacy of antiglaucoma therapy may occur.13-16 
  • Can be used in patients with primary infectious conjunctivitis (eg, feline chlamydial conjunctivitis), in contrast to corticosteroids
Vasoconstrictors, Antihistamines, & Mast Cell Stabilizers
  • Naphazoline (OTC, alpha agonist) 
  • Ketotifen fumarate (OTC, antihistamine/mast cell stabilizer)
  • Olopatadine hydrochloride (OTC, antihistamine/mast cell stabilizer)
  • Nedocromil (prescription, mast cell stabilizer)
  • Lodoxamide (prescription, mast cell stabilizer)

Topical vasoconstrictors, antihistamines, and mast cell stabilizers are alternative treatments for allergic conjunctivitis. Depending on the concentration, many prescription or over-the-counter (OTC) products can reduce ocular redness, irritation, and tearing secondary to surface allergies.

Dosage (Dogs, Cats)

  • One drop per affected eye
  • Frequency should be based on severity but is most commonly every 12 to 24 hours.

Key Points

  • Alternative option for some patients with allergic conjunctivitis
  • Efficacy and safety for the treatment of allergic conjunctivitis in dogs and cats have not been reported.
  • Many OTC eye drops (eg, ketotifen, olopatadine) contain antihistamines that also stabilize mast cells. 
  • Topical vasoconstrictors reduce redness; however, chronic administration is not recommended, as chronic hypoxia of the ocular surface and increased long-term (rebound) clinical signs are possible.17

References

For global readers, a calculator to convert laboratory values, dosages, and other measurements to SI units can be found here.

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