The consistently best treatment option for otitis caused by rods on cytology is a topical solution of trisEDTA mixed with enrofloxacin (4oz of trisEDTA with 12 cc of LA Baytril) filling the ear every 12 hours for 2 weeks.
NO ORAL antibiotics as they provide no benefit.
Oral high dose pred if the canal is extremely swollen and painful (for only 1 week).
Recheck in 2 weeks with cytology and if still severely infected based on cytology, anesthetize and flush the deep canal and bullae using an 8 fr red rubber catheter and LOTS of fluid.
then repeat the 2 weeks to TrisEDTA and Baytril treatment.
If still not improving on cytology, then culture and chase the results with concentrated antibiotic topicals.