Today's Veterinary Practice

MAY-JUN 2017

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66 DERMATOLOGY DETAILS PEER REVIEWED Antibacterial agents: These products are indicated when infection is present and cleansing solutions are insufficient. Most topical antibacterial products also contain glucocorticoids and antifungals. • First-line antibiotics most commonly used include products containing neomycin alone or in combination with other agents (Tresaderm, us.merial.com ) and gentamicin (Gentocin Otic; Otomax, merck-animal-health-usa.com ; Mometamax, merck-animal-health-usa.com ). Ototoxicity is reported with all gentamicin topicals. However, as with chlorhexidine, this concern may be overstated. One study showed no vestibulotoxic or ototoxic effects from 21 days of otic gentamicin applied q12h to ears with ruptured tympanic membranes. 13,14 Polymyxin B (Surolan, elanco.com ) can also be a highly effective topical antibiotic and often is effective in many Pseudomonas infections; however, polymyxin can be inactivated by purulent exudates. • Second-line antibiotics include tobramycin (Tobrex ophthalmic solution, alcon.com ), injectable amikacin mixed with saline at a final concentration of 25 mg/mL, and ticarcillin– clavulanate potassium, which may be ordered at compounding pharmacies. Care needs to be used with certain topical aminoglycosides because ototoxicity, based on brainstem auditory evoked response testing, was recently seen to occur more commonly in dogs treated with amikacin- and tobramycin-based topicals. 13,14 • Third-line antibiotics include mupirocin and fluoroquinolones, ideally based on C/S. Mupirocin should be saved for multidrug- and methicillin-resistant Staphylococcus infections; the product is mixed as 1 tube of product (30 g) to 30 mL of sterile saline. Enrofloxacin and silver sulfadiazine (Baytril Otic, bayerdvm.com ) is often ineffective in chronic severe cases. Injectable formulations of enrofloxacin (Baytril injectable) are preferable in many different extralabel recipes, such as a 25% mixture of injectable enrofloxacin (22.7 mg/mL diluted with water, saline, or other active agents with variable concentrations of dexamethasone, not exceeding 0.1% to 1%). Posatex ( merck-animal-health-usa.com ) contains orbifloxacin, posaconazole, and prednisone and may be used against multidrug-resistant infections, such as Staphylococcus and Pseudomonas infections. • Antifungal agents: These may be used in any otitis case associated with yeasts, such as Malassezia or Candida species. 10–13 Many available products contain glucocorticoids and antibiotics; however, products containing only antifungals can be found. Usually effective antifungals include clotrimazole (Otomax, Mometamax), miconazole (Conofite, merck-animal-health-usa.com ), thiabendazole (Tresaderm), acetic acid (MalAcetic Otic, dechra-us.com ), and TrizEDTA and ketoconazole flush (TrizUltra+Keto, dechra-us.com ). Glucocorticoids Numerous topical preparations of variable potencies are available for use in the external ear canal. 10–13 The frequency of use varies from q6h to q24h, depending on the product and the severity of the otitis. Most cases of chronic otitis externa benefit from topical glucocorticoids. Glucocorticoids have antipruritic, anti-inflammatory effects and decrease exudation and swelling, thereby helping to reduce pain and discomfort. In addition, they cause sebaceous atrophy and decrease glandular secretions. Glucocorticoids may reduce scar tissue and proliferative changes, which helps to promote FIGURE 7. Chronic Pseudomonas otitis.

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