Deafness --Surolan

Question
My 12 year old border collie, was put on Surolan (one drop twice a day in each ear) for an ear infection & yeast.  After 4 days we noticed he was not responding to his name, the doorbell etc.  He had gone completely deaf.  I discontinued the drops, called the vet who had prescribed them (not my regular vet) who said the drops could not cause this, it was just deafness from old age.  As he had no problem with his hearing prior to this I have no doubt it was caused by the drops.  She checked his eardrums which are fine but a week has passed and he is still totally deaf.  What are the chances his hearing will come back and how long might it take?  

Answer
Surolan contains polymyxin, which is an antibiotic that is very ototoxic to the inner ear.  If the deafness was caused by the drug, it may take a long time to reverse if it can.  If it is from something else, a large dose of a steroid medication given by injection may help take pressure off of the nerve going to the cochlea.