In this study, the stability and in vitro bactericidal activity of enrofloxacin in 4 different ear cleaners were evaluated. A 0.9% solution was made by adding 1.25 mL of 100 mg/mL enrofloxacin to 12.5 mL of each of the following commercial cleaners: tris-EDTA, tris-EDTA with 0.15% chlorhexidine, 2.5% lactic acid with 0.1% salicylic acid and 0.1% parachlorometaxylenol, and 0.1% salicylic acid with 0.1% parachlorometaxylenol and 0.5% EDTA. Sterile water was used as a control. Percent recovery of enrofloxacin from the cleaners and antibacterial activity against Staphylococcus pseudintermedius and Pseudomonas aeruginosa were tested on days 0, 14, and 28. The percent recovery between days 0 and 28 was >97% for all 4 cleaners and the sterile water. Bactericidal efficacy was seen with all the compounded solutions, although a significant decrease at day 14 was noted with tris-EDTA and 0.15% chlorhexidine solution. P aeruginosa was more sensitive to the compounded solutions than was S pseudintermedius.

Commentary
Although the stability and bactericidal efficacy of enrofloxacin compounded with commercial ear cleaners were documented, caution needs to be emphasized against making this a practice; an FDA veterinary-approved product containing enrofloxacin is available, and off-label products should only be used after FDA-approved products have been tried and proven ineffective. Fluoroquinolone antibiotics need to be used with care to minimize the development of resistant strains of both Pseudomonas and Staphylococcus. There is also the risk that a “one-step” cleaner and treatment product may result in inadequate treatment compared with the client cleaning the ear thoroughly and then applying otic medication. Other concerns include bottles of compounded ear cleaner kept and reused, use of the product in other pets without ear disease, and/or contamination of the applicator tip.1—Karen Moriello, DVM, DACVD

Source
Determination of enrofloxacin stability and in vitro efficacy against Staphylococcus pseudintermedius and Pseudomonas aeruginosa in four ear cleaner solutions over a 28 day period. Metry CA, Maddox CW, Dirikolu L, et al. VET DERMATOL 23:23-e6, 2012.

1. Bacterial contamination of commercial ear cleaners following routine home use. Bartlett SJ, Rosenkrantz WS, Sanchez S. Vet Dermatol 22:546-553, 2011.