I read the technical article on S. boulardii and it is SAFE for people with HIV-1. By critically ill people with weakened immune systems, that means people taking anti-rejection drugs or being naturally immunocompromised in some way. Just having an FIV+ kitty should not be a problem any more than an HIV-1 person would be. If it's working and the cat is responding, I would stick with it. For my 4 feral kittens who probably had giardia and coccidia and God knows what else, it worked. I could not handle them to medicate them with anything else. It took approximately one month to get consistently perfect poop in all four kittens, but it worked, and none of them are on anything special now.
As for making diarrhea worse, perhaps if the kitten has giardia or coccidia and they are now being pushed out by the S. boulardii, I suppose it's possible, but if it persists for more than 24-48 hours being more extreme than it was, who knows? Maybe a culture is in order? For mine, it just stayed the same gassy watery explosive stuff for awhile and then gradually got better, turned into cow pies, then one started forming tootsie rolls, then maybe 50% of the leavings were formed and the others were piles, and I didnt know who had which, and finally nobody had cow pies any more. I kept the boulardii up for another 2 weeks and then gradually cut it down and then out. All is still perfect, no bad smells either!
As for making diarrhea worse, perhaps if the kitten has giardia or coccidia and they are now being pushed out by the S. boulardii, I suppose it's possible, but if it persists for more than 24-48 hours being more extreme than it was, who knows? Maybe a culture is in order? For mine, it just stayed the same gassy watery explosive stuff for awhile and then gradually got better, turned into cow pies, then one started forming tootsie rolls, then maybe 50% of the leavings were formed and the others were piles, and I didnt know who had which, and finally nobody had cow pies any more. I kept the boulardii up for another 2 weeks and then gradually cut it down and then out. All is still perfect, no bad smells either!