My old timer was diagnosed with UTI too.
They threw so many different designer antibiotics at him that almost killed him. And none of them were working.
I finally insisted they do a culture on the urine. Two things. One was the antibiotic that showed up to work was of all things something as simple as amoxy! And they found it to be a 'kidney' infection not a urinary infection. And by then the kidneys were failing.
I always thought that if a dog was in kidney failure that was it for them. My home vet said no. What they do now and I forgot the term something like sineese?
What my vet did was put him on a VERY VERY slow drip of fluids taking all day to do for 5 days, then subQ for 5 days. And administering Amoxy.
Vet said what kills most of them is a vet rapidly shooting down bags of IV's into the dog.
I had to cancel my trip back down south and extend my stay at the CG up there, but when he was done with the treatment he was checked out A-OK and ready to travel back south just before the snow hit!
He's still here today sleeping under the computer table and looking pretty darn good for 16 years old. I love my Vet back home! :C