You notice your dog rubbing at his eyes, and when you take closer look, you see that they are red, inflamed with a thick, purulent discharge, and obviously painful. Your veterinarian suspects an eye disease and, upon examination, diagnoses a bacterial infection that involves the dog's cornea, the clear part of the eye. The rubbing has exacerbated the problem by causing abrasions on the cornea that are now infected. The appropriate drug used to treat the infection depends on the cause and severity of the disease, and the cure depends on your compliance with veterinary protocol.
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N-P-B
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Veterinarians prescribe N-P-B (a mix of neomycin, polymixin B and bacitracin antibiotics) as a topical treatment for eye infections and corneal abrasions and/or ulcers. These drugs destroy the aerobic bacteria causing the infection by disrupting the bacterial cell walls. Typically rendered in both a liquid and ointment preparation, N-P-B needs to be administered to the infected eye or eyes at least four to six times a day for seven to 10 days to be effective, says Dr. Alleice Summers in "Common Diseases of Companion Animals." Because the drugs in N-P-B are poorly absorbed through the intestinal tract, side effects are minimal.
Your vet might recommend N-P-B mixed with cortisone (a steroid) if your dog has an eye or corneal infection without any signs of ulceration. The added cortisone quickly restores the eye tissues to stasis (normal); however, it will retard healing cell production in the ulcer and is not recommended for that disease.
Topical Atropine
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To relieve the pain and inflammation associated with eye and corneal infections, veterinarians suggest atropine, a topical analgesic (painkiller) sold as a liquid or ointment. Atropine also stops the pain-induced eyelid spasms that can inflict further damage on your dog's eyes. The drug works by blocking the enzyme that allows nerve impulses sent to the brain to register as pain. Because atropine tends to reduce eye secretions, it is not recommended for patients with glaucoma.
Cyclosporine A
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Some corneal abrasions and subsequent eye infections are caused by the disease keratoconjunctivitis sicca, or "dry eye." KCS occurs when your pet's lachrymal (tear) glands stop producing an adequate amount of liquid to keep the cornea moist. The cornea can become cloudy and scarred, resulting in infection and eventual blindness. Cyclosporine A, sold as an ointment under the trade name Optimmune, replaces your dog's natural moisture. According to Dr. Robert Bill in "Pharmacology for Veterinary Technicians," cyclosporine restores production of "near normal" levels of tears, but affected dogs must be treated with cyclosporine "for the rest of their lives."
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