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Will antibiotics help For IBS If I have been diagnosed with SIBO?

Using patterns of the Lactulose Hydrogen Breath Test to Make Decisions regarding antibiotic therapy in IBS with Small Intestinal Bacterial Overgrowth

Small Intestinal Bacterial Overgrowth (SIBO) is an increasingly diagnosed pathophysiologic process that involves normal bacterial flora of the colon being irregularly and excessively translocated to the small intestine. In additions some will acquire SIBO by breakdown in mechanisms that normally clear bacteria from the small intestine such as the migrating motor complex. Once this bacteria has set up in the small intestine it can cause bowel transit dysregulation (diarrhea, constipation, or both), bloating, excess wind, and abdominal discomfort. Many top researchers feel it might be the underlying component of Irritable Bowel Syndrome. It is diagnosed by clinical symptoms combined with the Lactulose Hydrogen Breath Test (LHBT) which measures the production of Methane and Hydrogen case being emitted from the small intestine after an injection of a highly fermentable sugar called lactulose.

Testers will produce various levels of hydrogen and methane throughout the 3 hour test and based on the levels a diagnosis is made. The conventional treatment for SIBO is a round or more of specific antibiotics that reduce these bacteria from the small intestine. Traditionally Rifaximin has been the most used antibiotic. However Neomycin, Augmentin, Doxycycline, Levofloxacin, Ciprofloxacin, and Metronidazole have all been used. In most studies the efficacy of the aforementioned antibiotics in SIBO eradication is anywhere from 65 to 100%.

Not all LHBT test look the same. There are various patterns of gas production we see and even a positive LHBT test we see response to treatment highly variable. Recently Kasir and colleagues performed a retrospective chart review of 561 IBS patients with a positive LHBT to see which LHBT patterns best responded to antibiotics. (Kasir, et al., 2015)


Group 1 is considered what’s called a “flat line” where we do not see an elevation of hydrogen or methanogens greater then 20 ppm throughout the test. Group 2 has a 20 ppm rise or more within the first part of the test followed by a second peak greater than 1 ppm after 90 minutes in the test. Group 2 is most typical. Group 3 is has a >50 ppm rise after 90 minutes into the test but less than 50 ppm prior to that. And Group 4 are irregular patterns that don’t fit either of the categories. So here is what happened:

Group 1: 94.7% reported improvement after antibiotics

Group 2: 81.4% reported improvement after antibiotics

Group 3: 46.3% reported improvement after antibiotics

Group 4: 79.9% reported improvement after antibiotics

This is pretty telling as there is some question all together where the Group 3 pattern is even SIBO all together. If you look at the pattern most of the gas increase is happening at the end of the test. At this point we would expect that the lactulose solution is near regularly placed colon bacterial. Also if someone has SIBO in the further parts of the Small Intestine (ie. the ileum) it makes sense that the antibiotics might not have as high rate of delivery. However this is me speculating why group 3 fares so poorly. Whereas the other patterns clearly show a spike somewhere in the first part of the test indicating more obvious small intestinal organisms. But you caught me…what about pattern 1 and why did it fare so well. Most SIBO experts agree that the first group is actually producing a non-detectable gas called Hydrogen Sulfide. This is called a “flat line”. These folks clearly respond to treatment and should obviously be presented full treatment options.

What if you do not want to take antibiotics? Well certainly many herbal therapies exists that are antimicrobial in nature and are highly active against gram positive, gram negative bacteria, and even archaeal organisms. A qualified herbalist or Naturopathic physician can certainly help design treatment protocols.

It is important to point out that "improvement in this study does not mean resolution of IBS.

The treatment for IBS with SIBO is not usually a one off scenario. Addressing why it developed in the first place and preventing it from coming back is something that involves dietary factors, nutritional interventions, and microbiome balancing treatments.

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