David,

Has a urine CULTURE (not just a urinalysis) been performed on a STERILE (acquired through cystocentesis) urine sample? If not, I recommend you have that done right away. Only a culture can tell your vet exactly which, if any, bacteria is present in his urine. Without a culture, your vet can only prescribe "shotgun" broad spectrum antibiotics and hope that they'll be effective against any bacteria present. Knowing the specific bacteria present through a urine culture will allow your vet to prescribe an antibiotic with known efficacy against that specific bacteria.

Acquiring a sterile urine sample through cystocentesis (urine drawn directly from the bladder with a needle) is important because free-catch urine (urine that's been peed out) can easily be contaminated and return a false positive test result.

Once you have a culture from a sterile urine sample, you'll know for sure whether or not there actually is infection present. Blood can also appear in urine as the result of urinary crystals without infection or as a result of interstitial cystitis (inflammation of unknown cause of the urinary tract). If there is no infection present, antibiotics are useless, and other treatment options will need to be implemented.

Laurie

unresponsive urinary blood (hematuria) is often due to either a bladder stone (or stones)- most commonly... but it can also be the result of a bladder tumor. The first is usually easily picked up on a routine radiograph (a few rare stones, like those seen in Dalmations, or sometimes invisible on radiographs, but most show up easily). Bladder tumors large enough to bleed are easily picked up on ultrasound, and sometimes certain cells/chemicals in the urine will be detected by most professional laboratories... These problems will obviously not go away with more or better antibiotics, so I would recommend getting these tests done soon.