I suspect we have all come across that tricky Pseudomonas otitis case that just seem to refuse to completely respond to antibiotic therapy in spite of extensive investigation for underlying causes.
I had just one such case recently that, in spite of culture and sensitivity, blood work, skin biopsy, extensive flushing, lack of response to licensed products (and so on), just refused to respond.
A quick look through one of my trusty text books* suggested Ticarcillin.
Ticarcillin potentiated with calvulanic acid (Timentin) is an extended spectrum penicillin that often has good activity against Pseudomonas. The 100mg/ml antibiotic solution can be applied directly to the ear canal as a drop.
The case I’m treating has responded really well.
* Reference: Hill, P.B. (2002) Small Animal Dermatology: a practical guide to the diagnosis and management of skin diseases in dogs and cats. Butterworth-Heinemann. London.