Otitis topical and systemic - Proceedings of SCIVAC, 2007 - Rimini

otic medications are selected for cleaning, drying, and anti inflammatory or anti microbial properties. Parasiticidal agents are sometimes included, however they are often unnecessary. Vehicles and dispersion agents are also important in otic topicals. Topical glucocorticoids are valuable in most cases of otitis externa even when infection is present. Glucocorticoids have antipruritic, anti-inflammatory effects and decrease exudation and swelling. In addition they cause sebaceous atrophy and decrease glandular secretions. Glucocorticoids may reduce scar tissue and proliferative changes, which helps to promote drainage and ventilation. There are many different types and potencies of topical glucocorticoids available. It is best to choose several products of different potencies and become familiar with them. The more common active ingredients found in veterinary products are, from generally the weakest to more potent, 1% hydrocortisone, 0.1% triamcinolone, 0.1% dexamethasone, 0.1% betamethasone and 0.1% fluocinolone acetonide and mometasone furoate. The 0.1% products listed have been shown to cause adrenal suppression in normal dogs. Dexamethasone at 0.01% does not. (Aniya and Griffin 2007) Dexamethasone sodium phosphate 4 mg/ml actually contains 3mg of dexamethasone. This is used to make a variety of ear products in the clinic. Most commonly I make products with 0.1% which is 33% of the final product being the dexamethasone sodium phosphate or 0.066% which is 25% of the final mix being the dexamethasone sodium phosphate. My low strength for long term control of allergic otitis is 0.01% which is 1 cc of dexamethasone sodium phosphate with 29cc of other components, most often 1%miconazole lotion. Antimicrobial agents include disinfectants, antibiotics and antifungal (yeast) agents. Disinfectants and/or drying agents should be used after the ear is cleaned and relatively dry. They are also used to help prevent swimmers ear, for odor control and to control secondary infections and treat some difficult cases of resistant microbes such as Pseudomonas sp. Many, though not all, of the disinfectants have been shown to have antifungal activity including acetic/boric acid products, chlorhexidine, and silver sulfadiazine. In many cases disinfectants are used alone or in conjunction with antibiotic containing topical to manage many secondary infections. Disinfectants have the advantage of not inducing resistance and are often less expensive. Acetic acid has been shown to be very effective in the treatment of otitis externa in humans. It is believed that its activity is not completely due to the pH because other acidic products are not as effective in killing Pseudomonas and Staphylococcus. It is possible to get a disinfectant effect just by lowering the pH of the ear canal. Advanced pHormulaTM Ear Cleanser (Evsco pharmaceuticals) uses novasome technology to and citric acid and sodium citrate to maintain the pH of the ear canal below 5 for 18 hours. Another study evaluated 2.5% lactic acid and 0.1% salicylic acid in propylene glycol (Epi-Oitc®, Virbac) showing efficacy in 67.7% of clinical cases (Cole, Kwochka et al. 2003). Acetic acid is effective against Pseudomonas, with a 2% solution being lethal within one minute of contact (Thorp, Kruger et al. 1998). White vinegar is generally about 5% acetic acid and it has been recommended as an ear wash when diluted to 2.5% by mixing it in equal amounts with water or 25% water, 25% isopropyl alcohol and 50% white vinegar. Combinations with 2% boric and 2% acetic acid are available commercially. (Malacetic, Dermapet® and Otocetic solution, Vedco) Aluminum acetate (Burow’s solution) has also been shown effective for many ear pathogens and as effective as a polymyxin/hydrocortisone eardrop or gentamicin in a group of acute otitis externa cases in humans that were often associated with swimming and 34% had Pseudomonas pyocyanea infections (Lambert 1981; Clayton, Osborne et al. 1990; Thorp, Kruger et al. 1998). In one of these studies stinging from the aluminum acetate drops resulted in their being discontinued in 5% of the cases treated, however another study had no reports of reactions so the formula used may also contribute to reactions. Burows solution may take 20 minutes of contact to kill organisms(Kashiwamura, Chida et al. 2004). The aluminum can bind and inactivate fluoroquinolones so this type of product should be avoided if concurrent therapy with a topical containing fluoroquinolone is contemplated. A veterinary product of this type is Bur-Otic®-HC Ear treatment (Virbac) and as a sole therapy should be used three times a day or more. Tris EDTA increases the permeability of bacterial cell membranes by binding Ca and Mg ions. This activity is mainly apparent in gram negative bacteria including Pseudomonas sp. It is used as a rinse prior to antibiotic application or even mixed with antibiotics to make a combination topical therapy. This combination allows more of the antibiotic to penetrate intracellular, even in some resistant strains making them now susceptible. They are synergistic with multiple antibiotics not just aminoglycosides as was originally thought. TrisEDTA was shown to have a sparing effect on the MIC of enrofloxacin against ciprofloxacin resistant Pseudomonas as well as resolve clinical cases resistant to cephalosporin or enrofloxacin(Farca, Piromalli et al. 1997; Gbadamosis and Gotthelf 2003). It was also shown effective in vivo in a small number of cases when combined with a low level (0.15%) of chlorhexidine digluconate(Ghibaudo, Cornegliani et al. Otitis topical and systemic