It's simple microbiology. You put one type of bug in a petri dish, you try different types of antibiotics, you see what kills it--and what *doesn't.* It's the same reason antibiotics are given for anything--particular antibiotics for particular types of bugs. For c-diff, for instance, [*not* one of the bugs implicated in SIBO but something you can get in the *colon* if *other* antibiotics kill off your normal colonic flora--which situation can, btw, make diarrhea worse; if you spike fevers at night too it's usually c-diff] *only* flagyl/metronidazole and vancomycin work. Vanco works here *because* it's not well-absorbed from the colon; it stays there.So an added plus is that certain antibiotics do stay in the gut, and rifaximin is another one.Pimentel could not *afford* to publish in the gastro *journals* he does [ya can say anything in a book] if he had not checked to see which types of bugs were popping up and which antibiotics would be ineffective. My GI doc is an older, conservative guy, and *he* likes the breath test and standard antibiotics. But it *is* new enough that OSU, a teaching hospital, doesn't give it. And my PCP, whom they *brought* here to teach diagnostics, is all about the test. Let me just say that in personal experience a lot of things that are new are pooh-poohed. I can tell you from personal experience that a lot of things in med school are taught by memorization/check the box/match the numbers. The people who like to do that and don't like to *think* instead, who don't like change, and who aren't all about continuing education, are often the ones doing the pooh-poohing. There's an excellent article just now on the SIBO site. And it also mentions the cleansing wave, and studies that show many IBSers have distorted or altered cleansing waves. [Meaning to look up that reference and see how they measured that...] Gilly's right, that is what the zelnorm is for: to keep the bugs from moving back 'north' once the drugs stomp 'em out of the small intestine. Article has a great description of the wave, too.