advice and what to expect

My wife has a 15 year old feline male that has chronic diarrhea. We took him to the vet and was told he has a infection. We were given Metronidazole and a IV solution with zero results.

The second diagnosis is IBD. Along with the above medication, he is on Prednisolone. Again, no results.

He is active. Never been a outside cat nor did he have contact with other animals. He is taking food and water. He isn't as affectionate as he was, but considering being forced medication, I'm not surprised.

He has lost a significant amount of weight and it about two pounds under ideal weight.

We are taking him in for a ultrasound but I'm looking for anything that might be helpful or what we can expect next.

Thank you.

Did they do a fecal float, just to check for any parasites that might be causing this.

Also, when they diagnosed IBD, did they do that simply based on symptoms.  Did they at that time suggest a change in diet?  Of course, I have no idea what you are feeding him, so possibly it doesn't need changing, but diet plays a HUGE part in helping with IBD.  Is he eating dry food or canned food.  Dry food is not good for cats with IBD, as it normally contains wheat, corn, soy, those type of products that aggravate IBD. 

OR, he could have a food sensitivity to a specific item in the food, even chicken, which could only be determined by an elimination diet.  First things first though.  Let's see what the Ultrasound shows.