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It is possible this may do no good at all. Most dogs get yeast infections in their ears, and an antibiotic will do nothing in these cases. The medication they need is an anti-fungal, and floxin is an antibiotic.
You should visit the vet, who will take a sample of the material in the ear and determine if, in fact, this is a yeast or a bacterial infection. Bring along your medication in case your vet feels it could be appropriate, but I would plan on a different medication being needed.
Good luck and let me know if you have more questions!