Today's Veterinary Practice

JUL-AUG 2014

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| Diagnosis & TreaTmenT of KeraToconjuncTiviTis sicca in Dogs Today's veterinary Practice July/August 2014 20 tvpjournal.com olive oil solutions; they may be more effective, but may also be more irritating to the eye. Therapeutic recommendations. Apply ¼-inch strand of topical CsA Q 12 H, with a recheck STT in 1 month. For optimal results, perform the STT approximately 3 to 4 H after application of CsA. Treatment failure can be diag- nosed only after 12 weeks of consistent topical application. If treatment fails, attempt treatment Q 8 H or initiate treat- ment with tacrolimus. With long-term use, CsA decreases corneal pigmentation and vascularization, even in patients that do not experience increased tear production; therefore, its use is often con- tinued in these patients. 18,24 2. Tacrolimus Mechanism of action. Tacrolimus has a similar, but more potent, mechanism of action compared with that of CsA. Efficacy. Patients that are unresponsive to CsA may respond to tacrolimus. 26,27 Formulation. Tacrolimus is generally compounded to a 0.03% ophthalmic aqueous suspension; however, formula- tions may vary. Therapeutic recommendations. Apply 1 drop of topical tacrolimus Q 12 H, with a recheck STT in 1 month. Continue treatment for several months before considering treatment failure. In addition to increasing tear production, tacrolim- us may decrease clinical signs, such as pigmentation asso- ciated with chronic KCS, even if tear production does not increase, but no long-term studies exist. Tacrolimus use for treating KCS in dogs is off-label; there- fore, the U.S. Food and Drug Administration approved therapy—CsA 0.2% ophthalmic ointment (Optimmune)— should be used as first-line treatment, with tacrolimus reserved for cases unresponsive to CsA. 3. Pilocarpine Mechanism of action. Parasympathomimetic drug (stimu- lates or mimics the parasympathetic nervous sytem). Upreg- ulation of parasympathetic receptors secondary to denerva- tion results in increased sensitivity of the lacrimal system to pilocarpine when compared with the rest of the body. 9 Efficacy. May be used to stimulate tear production in cases of neurogenic (quan- titative) KCS. These cases are diagnosed when ipsilateral dry nose is present in conjunction with a low result on STT. Formulation. 1% or 2% solutions Therapeutic recommendations. Sprin- kle 1 to 2 drops of 2% pilocarpine per 10 kg on top of food Q 12 H. System- ic administration of pilocarpine is pre- ferred because it can be irritating when applied topically. 28 Note that pilocarpine has a narrow therapeutic window, and while some cli- nicians advocate increasing the number of drops applied to food by 1 drop each day until systemic adverse effects are observed—such as vomiting, diarrhea, ptyalism, anorexia, and bradycardia—we prefer to avoid these effects by only increasing the total dose by 1 or 2 drops before consider- ing pilocarpine ineffective. Client education about adverse effects is important. Tear Replacement Tear replacement therapy provides lubrication until tear stimulants are effective. Lifelong tear replacement therapy may be needed in dogs that never respond to CsA or tacro- limus. These medications are available as solutions, gels, and ointments, and have a wide variety of constituents. 1. Artificial tear solutions commonly contain 0.1% to 1.4% polyvinyl alcohol. Artificial tear solutions are useful for removing debris and mucus from the ocular surface; however, they are not feasible as monotherapy in most dogs with KCS due to the need for frequent application in order to achieve adequate lubrication. 2. Cellulose-based solutions/gels and viscoelastic prod- ucts are more viscous and have slower evaporation times than artificial tear solutions. They require application Q 4 to 6 H. Examples of cellulose-based solution and viscoelastic products are hydroxypropyl and hyaluronate, respectively. 3. Artificial tear formulations containing petrolatum, mineral oil, or lanolin are the most viscous products and provide long-term lubrication, but can result in debris accumulation. They are best suited for patients with: • Lipid layer deficiencies • Lagophthalmos (administered prior to sleep) • Owners who will be absent for long periods. Antibiotics A severe, mucopurulent discharge suggests a secondary bacterial infection. Generally, use a broad-spectrum oph- thalmic antibiotic, such as triple antibiotic ointment (neo- mycin/bacitracin/polymyxin B) Q 6 to 8 H for approxi- mately 2 weeks. If empirical treatment fails to resolve the discharge, perform culture and sensitivity. Figure 7. Seven-year-old spayed female miniature pinscher. Note corneal vascularization and pigmentation; STT was 7 mm/min (A). Same patient 3 months after topical CsA therapy; note resolution of corneal vascularization and thinning of pigment (B). A B

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