ANTIBIOTIC & CORTICOSTEROID COMBINATIONS (OPHTHALMIC)

Indications/Pharmacology

There are three basic categories of these products that are routinely used inveterinary medicine; antibiotic combinations with hydrocortisone, antibiotic combinations withdexamethasone, and individual antibiotics (e.g., gentamicin or chloramphenicol) with a steroid.
Antibiotic combinations with hydrocortisone (ointment or solution) are used in dogs and horses forconjunctivitis as nonspecific therapy after ruling out other causes for red painful eyes, including glaucomaand anterior uveitis. They generally are applied 4 times daily and then on a tapering schedule based on theresponse to therapy. The hydrocortisone is relatively weak as an antiinflammatory agent and is noteffective for intraocular inflammatory disease such as anterior uveitis. The relative penetration andpotency of hydrocortisone in these preparations makes them relatively ineffective for immune mediatedextraocular disease including scleritis, episcleritis and or nodular granulomatous episclerokeratitis.
Anterior uveitis is statistically more common in horses than simple conjunctivitis and the steroid in theseagents would not be helpful in improving the clinical signs of immune mediated uveitis.
Antibiotic combinations with dexamethasone are valuable for use in cases of more severe canine orequine conjunctivitis, nonulcerative keratitis and for immune-mediated scleral or corneal conditions suchas chronic superficial keratitis (German Shepherd pannus), feline eosinophilic keratitis, scleritis, episcleritis and nodular granulomatous episclerokeratitis. For these conditions the antibiotic agent is notnecessary but dexamethasone-only products are not always available. These medications are also used inthe equine species with equine uveitis because the ointment forms persist on the cornea longer than dropsand because they are less expensive than prednisolone acetate ophthalmic suspensions.
Single agent antibiotic (gentamicin) and potent steroid (betamethasone) combination products (e.g.,
Gentocin Durafilm®) are commonly used in veterinary medicine. However, there are few instances inveterinary ophthalmology in which a very potent corticosteroid agent and an aminoglycoside antibioticare necessary in combination. Simple conjunctivitis in dogs and horses is adequately treated withantibiotic combinations with hydrocortisone. Avoid use of this agent in cats with conjunctivitis for thereasons noted below.Suggested Dosages/Precautions/Adverse Effects - See individual product label information and theinformation noted above.
Avoid use of antibiotic/steroid combination agents in cats with conjunctivitis as the most common causeof conjunctivitis in the cat is primary or recurring infection with exposure to, or reactivation of, latentfeline herpes virus. Recent research indicates that topical steroids increase the length of the typical courseof feline herpes virus related conjunctivitis and/or keratitis and can induce corneal involvement in caseswhich might otherwise have remained confined to conjunctiva. Corneal sequestration has been noted tooccur in cats with herpes virus conjunctivitis after treatment with topical steroids. Recommendedtreatment for feline herpes virus conjunctivitis is tetracycline ointment QID during active disease, as thisdrug is effective against Mycoplasma and chlamydia (other causes of infectious conjunctivitis in the cat).Dosage Forms/Preparations/FDA Approval Status - Veterinary-Approved Products:
Triple Antibiotic Ointments with Hydrocortisone:
Bacitracin zinc 400 units/Neomycin 3.5 mg/Polymyxin B Sulfate 10, 000 Units & Hydrocortisone acetate 1% per gram in 3.5 gm tubes Neobacimyx H® (Schering); Trioptic-S® (Pfizer);
Vetropolycin HC®- (Pitman-Moore); Generic. All are Rx and approved for dogs and cats.
Other Antibiotic/Steroid Ointments:
Neomycin Sulfate 5 mg & Prednisolone 2 mg (0.2%) per gram in 3.5 gram tubes (Optisone® - Evsco); (Rx). Approved for use in dogs and cats.
Neomycin Sulfate 5 mg & Isoflupredone acetate 1 mg (0.1%) per gram in 3.5 & 5 gram tubes
Neo-Predef® Sterile Ointment® (Upjohn); (Rx). Approved for use in horses, cattle, dogs and cats.
Chloramphenicol 1% and Prednisolone acetate 2.5 mg (0.25%) in 3.5 gm tubes; Chlorasone® (Evsco) (Rx). Approved for use dogs and cats.
Drops:
Gentamicin Ophthalmic Drops 3 mg/ml & Betamethasone acetate 1 m/ml in 5 ml btls Gentocin
Durafilm® (Schering); (Rx). Approved for use in dogs.

Human-Approved Products:

There are a wide variety of human-labeled ophthalmic antibiotic/steroid combination products available. Some of the more commonly used combinations include:
Ointments:
Bacitracin/Neomycin/Polymyxin B and Hydrocortisone Cortisporin® (BW)
Neomycin/Polymyxin B & Dexamethasone Maxitrol® (Alcon); (Rx)
Neomycin and Dexamethasone NeoDecadron® (Merck); (Rx)
Drops:
Neomycin/Polymyxin B and Hydrocortisone Cortisporin® (BW, etc.); (Rx)
Neomycin/Polymyxin B & Dexamethasone Maxitrol® (Alcon); (Rx)
Neomycin and Dexamethasone NeoDecadron® (Merck); (Rx)
Antifungals (Ophthalmic)
Fungal keratitis is a serious corneal disease, most commonly reported in the horse. The speciesselectivity of this disease is related to the environment of this animal, which is often contaminated withfungal elements. An increased incidence of fungal keratitis in people was directly related to thedevelopment of multiple topical steroid agents for treatment of eye diseases. In the horse, many cases offungal keratitis are noted in association with prior treatment of conjunctival and/or corneal diseases withtopical steroid agents. Aspergillus is the most common cause of fungal keratitis in the horse, althoughthere is a great deal of variation in fungal isolates from the cornea depending upon geographical location.
Studies in people and anecdotal reports from veterinarians suggest that fungal keratitises due to Fusariumorganisms are more resistant to therapy than are those caused by aspergillus. Most studies in the equinesuggest that about 50% of cases of fungal keratitis in the horse result in perforation of the corneal andenucleation of the eye. Medical and surgical therapy (keratectomy, corneal debridement, and conjunctivalgrafting) are used to treat such cases with the goals of therapy including arresting infection, mechanicalremoval of organisms from the cornea, and support of the cornea. All antifungal agents available for usein the equine suffer from poor penetration into the corneal stroma. Conjunctival grafting may furtherhinder drug penetration as a trade off to improving vascular availability to the cornea and mechanicalsupport. Pathologic specimens from horses with fungal keratitis indicate that fungal organisms, unlikebacterial organisms, have a propensity to multiply deep in the stroma, directly adjacent to Descemet'smembrane, making corneal penetration an important issue. Because the prognosis for return of vision andsaving the globe in cases of fungal keratitis cases is guarded and because treatment is labor intensive, referral to teaching or other hospitals for 24 hour care and observation is recommended.