Veterinary Medicine - August 2007 - (Page 543)

bacteria demonstrate variable susceptibility to fluoroquinolones. Gatifloxacin, ofloxacin, and ciprofloxacin all penetrate an intact corneal epithelium; however, gatifloxacin offers the best penetration.6-8 The only other topical antibiotic capable of penetrating intact corneal epithelium is chloramphenicol, which is infrequently used because, though rarely, it can cause aplastic anemia in people. tered topically twice daily.10 The drug also causes little irritation.10 The lack of irritation and decreased frequency of administration make compliance much easier than treating with idoxuridine or trifluridine. Cidofovir must be compounded for ophthalmic use. tion should be considered when selecting which formulation to use. GLAUCOMA MEDICATIONS Several relatively new topical medications are available to assist in controlling intraocular pressure (IOP) in dogs and cats with glaucoma. While these medications do not cure glaucoma, they do aid in maintaining better control of IOP and in preventing IOP increases in the normotensive eye of patients with primary glaucoma. Famciclovir Systemic antivirals may be required for animals that resist topical application or for those cats with dermatologic or other systemic signs related to FHV-1 infection. Famciclovir (Famvir— Novartis) is a new oral antiviral medication that shows promise in cats. At a dosage of 90 mg/kg given orally three times a day for 21 days, no signs of toxicosis were reported, and the treated cats had significantly lower clinical disease scores than the untreated cats had.11 Anecdotally, some practitioners are administering 1/8 to 1/4 of a 125-mg tablet of famciclovir once daily and seeing an improvement in clinical signs. ANTIVIRAL MEDICATIONS Antivirals that are now available include idoxuridine, trifluridine, cidofovir, famciclovir, and lysine. Topical carbonic anhydrase inhibitors Topical carbonic anhydrase inhibitors offer the same decreases in IOP that systemic carbonic anhydrase inhibitors such as acetazolamide and methazolamide do but without the systemic side effects. Topically administering 2% dorzolamide (Trusopt—Merck) or 1% brinzolamide (Azopt—Alcon) every eight hours significantly decreases IOP by decreasing the rate of aqueous humor formation.13 Therapy will continue as long as the IOP can be controlled. Many patients with glaucoma undergo enucle- Idoxuridine and trifluridine Idoxuridine and trifluridine are available as topical antiviral drugs. Both are nucleoside analogues, structurally similar to the nucleosides used in viral and host DNA and RNA synthesis. Their substitution into viral DNA disrupts the virus replication cycle.9 Idoxuridine must be compounded and is typically used as a 0.1% solution. One drop is applied four to six times daily for one week past the resolution of clinical signs. While it is fairly efficacious, some irritation (blepharospasm and redness) may be noted. Trifluridine is available commercially for use in people as a 1% solution. Apply one drop four to six times daily for one week past the resolution of clinical signs. Trifluridine has excellent in vitro activity against feline rhinotracheitis virus (FHV-1) but is often not well-tolerated by patients.9 For example, it may cause ocular irritation and a stinging sensation upon application. Moreover, trifluridine costs about $100 for a 7.5-ml bottle. With either drug, the required frequent application often leads to poor owner compliance and undue stress for the patient. Lysine For cats that suffer frequent bouts of recrudescent disease, lysine may help. Lysine may help cats that suffer frequent bouts of recrudescent herpesvirus infection. While lysine alone will not eliminate a herpesvirus infection, lysine can decrease the severity of clinical signs and increase the time between recurrences.12 Lysine is typically dosed at 250 mg orally twice daily for kittens and lifelong at 500 mg orally twice daily for adult cats. Lysine is safe; however, it should be administered with food since it may induce vomiting if given on an empty stomach.12 Several veterinary and human formulations (e.g. powder, paste, gel, tablet) of lysine are available, and ease of administraation once vision is lost and the IOP cannot be adequately controlled. The combination of dorzolamide with oral methazolamide does not result in any greater decrease in IOP than administration of either product alone,14 so only administer a topical carbonic anhydrase inhibitor. Topical beta-blockers Topical beta-blockers can also be used to decrease aqueous humor production and, thereby, decrease IOP. The two most commonly used beta-blockers in Cidofovir In a 0.5% solution, cidofovir, an acyclic analogue of cytosine,9 decreases clinical signs of FHV-1 infection when adminis- VETERINARY MEDICINE August 2007 543

Table of Contents Feed for the Digital Edition of Veterinary Medicine - August 2007

Contents A Veterinary Medicine Interview Veterinary Voices Idea Exchange Diagnosis and Treatment of Solar Dermatitis in Dogs Diagnostic Imaging for Linear Foreign Bodies in Cats Overcoming the Diagnostic and Therapeutic Challenges of Canine Immune-Mediated Thrombocytopenia Ophthalmic drugs: What’s new? CE Form Product Preview Advertiser Index Marketplace/Classifieds Mind Over Miller

Veterinary Medicine - August 2007

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