Acute Peritonitis - tablets no longer working

My Gladys was diagnosed with acute peritonitis around 12 months' ago.  She has been having oxytetracyclene tablets, but these no longer seem to be having any effect.  She has permanent diarrhea (no  sickness), but now the tablets are no longer working she is dripping runny poop all over the house and her rear end is permanently soiled and smelly!  Vet says there are other medications to try.  Anyone have any ideas what I can do for her?

If your Vet says there are other medications to try, is there some reason you are reluctant to try them? 

With this particular issue, I would think that's what you should do.

Sorry, I missed out a word.  Vet says there are NO other tablets to try.  We did try various before the oxytetracyclene and none made an iota of difference.
 

Oh dear...well that makes a world of difference .

So, has he said she has FIP, or just acute peritonitis?  I honestly don't quite understand the difference.  I always thought "acute" meant short term, so it would probably go away in time.  So is it just a waiting game for this to go away, or what?  If so, have you tried adjusting her diet?  What do you feed her?  Does she get a good probiotic, since obviously the issues are in her digestive tract.   And I'm guessing what she was on was some sort of antibiotic, which absolutely destroys even the good bacterial in ones digestive tract, so maybe that's what she needs, is a really good probiotic.  We give all of our cats the same one we take.  this one  .  They each get one capsule per day sprinkled into their wet food.  I would say it's worth a shot