Hi, welcome! There has been quite a bit of discussion here about probiotics. You might try a search for "probiotics" and also try starting a new topic with your question -- that way more people will see it & know what it's about.
I'm in the 12th month of treatment with Azithromycin, ethambutol and either a placebo or Arikayce (clinical study med). I take florastor at my GI doc's recommendation. I have not had gi side effects other than very mild nausea at first. Florastor has been studied for effectiveness with antibiotics. It's more expensive but I decided it's worth it.

Hi. I’ve taken the Big 3 for more than a year with no side effects. I just make certain that I have a small meal when I take the daily meds. twice a day. I’ve read accounts of individuals experiencing some symptoms but fortunately, I’ve had none. I think everyone is different so it’s an individual thing. Good luck and try not to worry. It’s quite a lot of meds, especially if, like me, I’ve rarely taken medication in the past, but hopefully it’ll work well for you too.

Hi, my doctor had me take azithromycin every other day after a full dinner meal and I took the rifampin on an empty stomach before lunch the next day and then ethambutol after dinner also on that day. That schedule seemed to be most tolerable with regard to controlling GI issues. Also, I found that if I did not have vegetables in my dinner meal the day I was taking azithromycin, that helped too. I would just eat them at lunch in a salad for example. I took a VSL3 probiotic every day in the late evening before bed. VSL3 is cold packed because it contains live bacteria and you keep it in the refrigerator. I found that was the best probiotic for me. Good luck with your treatment!