Chronic Bladder infections - FUS

My cat, Joey, is a 14 year old neutered male. Approximately 3 months ago, he started peeing outside of the litter box. Fortunately, we keep puppy pee pads around each litter box to help minimize the mess and he ALWAYS pees on these pee pads right next to to litter boxes. He poops in the box. We have 7 cats and 8 boxes. We scoop every day and completely change the litter every 3-4 days.

First vet visit, the doctor found bacteria in the urine. I saw this under the microscope. There was a small amount of bacteria. (I have a bachelor's degree in Medical Technology and worked as a Medical Lab Tech for 10+ years.) No blood in the urine. No visible blood on the pee pads. No crystals in the urine. The doctor sent us home with Clavamox, which we gave exactly as instructed. After 2 days on the Clavamox, Joey started peeing in the box again. I thought the problem was solved, but no. After about 1 week on Clavamox, he started peeing on the pee pads again.

Three weeks after the initial visit, we went back to the vet. There was still bacteria in the urine. (The urine was obtained using a needle inserted directly into the bladder after shaving Joey and cleaning his skin with alcohol.) The doctor did an ultrasound to check for crystals. No crystals. No blood in the urine. Also, we did blood tests - all normal. (CBC, Chemistry panel, Thyroid hormone.) The doctor added a second antibiotic and we continued using the Clavamox simultaneously. I don't remember the name of the second antibiotic. It was bright yellow, liquid, & smelled fruity. Again, Joey started to use the box again but went back to the pee pads after a few days.

Six weeks after initial visit: back to the vet. Still bacteria present, but less. Still no blood, no crystals. Urine obtained via needle aspiration from bladder. The doctor prescribed Orbax. We were told to put Joey on Hills c/d. We isolated Joey from the other cats, gave him his special food and his own litter box. He refused to eat for two days. He drank water but didn't eat. This really worried me so I went back to giving him regular food - canned Friskies and/or Fancy Feast, plus Fancy Feast dry food. Again, he used the litter box for a couple days but then started peeing on the pee pads.

9 weeks after initial visit: (Last night: 18 May 2015) back to the vet. A lot more bacteria in the urine. Joey pees about once a day now & it's a huge amount. It doesn't ever look bloody and I don't see any red blood cells under the microscope. The vet did another ultrasound for crystals. He also did an x-ray. NO crystals. The vet gave us a new food: Urinary SO by Royal Canin. So far, he won't touch it. The vet gave us Clavamox again. He also gave us amitriptyline to "help with anxiety." This morning, after one dose of Clavamox, Joey peed in the box. I haven't tried the amitriptyline yet because I don't like the idea of putting him on an anxiety drug.

I am starting to wonder if it's time to see a new vet. Does anyone have experience with this situation? Isn't "FUS" associated with crystals? Joey hasn't had any crystals. How can he have so much bacteria in his urine? Why haven't the antibiotics helped? I feel so bad for him - I don't want him to be in pain!

Suggestions anyone?

What are your thoughts/experiences with amitriptyline?

Thank you!

since your cat has had no crystals and won't eat the prescription food, i would suggest an all wet diet with over the counter urinary health foods -- Friskies Special Diet or Purina Pro Plan Urinary Health

First, FUS is associated with ANY urologic syndromes, including urinary tract/bladder infections  (or so I've read )

Second, depending on WHEREand WHEN  the urine cultures were done, bacteria can multiply quickly in the urine once outside the body.  I refer you to this quote from: http://www.vet.cornell.edu/fhc/health_resources/urinary.cfm:

"Another thing to consider is how long and in what manner the urine sample was stored prior to submission to a laboratory for bacterial culture. A lot can happen between the time a sample leaves the cat's bladder and arrives at the laboratory (for example, bacterial counts can double every 20-40 minutes in warm urine). To be on the safe side, veterinarians may choose to check with the laboratory to determine their preferred method of sample handling and submission."

Next, did the lab do a sensitivity test to determine WHICH antibiotic would work best to erradicate the specific bacterial in YOUR cat?  There are many difference bacteria's out there, and different antibiotics "kill" different bugs. 

Additionally, with this type of bacterial infection, my understanding is it can take weeks of antibiotic therapy to nip it in the bud

I dn't know if any info on this site will help you, but maybe?  http://www.marvistavet.com/html/urinary_tract_infection.html