Small Intestinal Bacterial Overgrowth

Patient Guideline Summary

Publication Date: February 1, 2020

Last Updated: March 2, 2023

Objective

This patient summary means to summarize key recommendations from the American College of Gastroenterology (ACG) for the diagnosis and treatment of small intestinal bacterial overgrowth. This patient summary is limited to adults 18 years of age and older and should not be used as a reference for children.

Overview

Small intestinal bacterial overgrowth is a clinical syndrome of gastrointestinal (GI) symptoms caused by the presence of large numbers of bacteria within the small intestine. This bacterial overgrowth results in GI signs and/or symptoms. For example, the pathologic fermentation of food could lead to the production of excess gas and bloating.

We will use the abbreviation SIBO throughout this summary to refer to small intestinal bacterial overgrowth.

Abdominal pain, bloating, gas, distension, flatulence (passing wind), and diarrhea are the most common symptoms described in patients with SIBO. The most common of all of them is bloating.

The causes of SIBO vary and may need to be known to best prevent a recurrence.

Diagnosis of SIBO

Your doctor may use breath testing (a measurement of exhaled hydrogen gas in the breath after taking a fixed quantity of a carbohydrate such as glucose [75 g] or lactulose [10 g]) to confirm the diagnosis of SIBO if:
- you have irritable bowel syndrome (IBS), because some patients with IBS have SIBO.
- your symptoms suggest a motility disorder.
  - Motility disorders are caused by nerve or muscle problems (for example: scleroderma and diabetes) or by medications such as opioids, antidiarrheals, or anticholinergics, that slow the bowels and encourage bacterial overgrowth.
- you are symptomatic (abdominal pain, gas, bloating, and/or diarrhea) from previous abdominal surgery.
ACG does not suggest the use of breath testing for the diagnosis of SIBO if you don’t have symptoms and are using proton-pump inhibitors (PPIs) (drugs used for acid indigestion).
If you have constipation, your doctor may test for methane using glucose or lactulose breath tests to diagnose an overgrowth of methane-producing organisms called intestinal methanogen overgrowth (IMO).
The presence of excessive methane on breath testing does not indicate SIBO since methanogens are not bacteria (they are other organisms called archaea). So, we use the term IMO.

Treatment of SIBO

If you have symptoms of SIBO, your doctor may prescribe antibiotics to eliminate overgrowth and relieve symptoms.

The following table lists the suggested antibiotics for treatment of SIBO

Antibiotic	Dose
Rifaximin	550 mg t.i.d.
Amoxicillin-clavulanic acid	875 mg b.i.d.
Ciprofloxacin	500 mg b.i.d.
Doxycycline	100 mg q.d. to b.i.d.
Metronidazole	250 mg t.i.d.
Neomycin	500 mg b.i.d.
Norfloxacin	400 mg q.d.
Tetracycline	250 mg q.i.d.
Trimethoprim-sulfamethoxazole	160 mg/800 mg b.i.d.

q.d.: one time a day
b.i.d.: two times a day
t.i.d.: three times a day
q.i.d.: four times a day

There is a lack of consistent data for the use of specific probiotics (good bacteria) in the treatment of SIBO.

There is no basis for the use of fecal microbiota transplant in the treatment of SIBO.

A focus on prevention of SIBO is important to avoid the need for repeated use of antibiotics. Treatment of the underlying cause represents the primary method of prevention.

Abbreviations

ACG: American College Of Gastroenterology
GI: Gastrointestinal
IBS: Irritable Bowel Syndrome
IMO: Intestinal Methanogen Overgrowth
PPIs: Proton-pump Inhibitors
SIBO: Small Intestinal Bacterial Overgrowth
b.i.d.: Twice A Day
q.d.: Once A Day
q.i.d.: Four Times A Day
t.i.d.: Three Times A Day

Source Citation

Pimentel, Mark MD, FRCP(C), FACG; Saad, Richard J. MD, FACG; Long, Millie D. MD, MPH, FACG (GRADE Methodologist); Rao, Satish S. C. MD, PhD, FRCP, FACG. ACG Clinical Guideline, The American Journal of Gastroenterology: February 2020 - Volume 115 - Issue 2 - p 165-178 doi: 10.14309/ajg.0000000000000501

Disclaimer

The information in this patient summary should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health.