This is a randomized, double-blind, placebo-controlled study to evaluate the efficacy of ciprofloxacin versus metronidazole versus placebo in eradication of small intestinal bacterial overgrowth (SIBO).

Approximately 180 study subjects with SIBO identified by positive glucose hydrogen breath (GHB) testing who meet inclusive and exclusive criteria will be randomized to receive either ciprofloxacin 500mg by mouth twice daily, metronidazole 500mg by mouth twice daily, or placebo by mouth twice daily. Subjects will complete a baseline symptom questionnaire and be treated for 14 days. Response will be assessed at end of treatment. The Gastrointestinal Symptom Rating Scale (GSRS) and GHB testing will be performed at the end of treatment. Subjects with a negative GHB at the end of treatment are considered as cured, or treatment success. Patients with treatment success will be reassessed for long-term response to treatment or disease recurrence at 30 days, 4 months, and 9 months using GHB. Symptoms will also be re-assessed at the 30 day, 4 month, and 9 month intervals with GSRS-IBS symptom questionnaire done prior to GHB testing.

Inclusion Criteria:

• Adult patients age greater than 18 who have been diagnosed with SIBO after a clinically indicated hydrogen breath test.
• Patients with liver disease or liver cirrhosis will be included, as this particular group is at higher risk for developing SIBO, would potentially benefit from inclusion, and do not require dose adjustments with either study medication.
• Patients on warfarin are not excluded, but INR will be uniformly recommended to be checked within 1 week of therapy initiation, as standard practice through the Coumadin clinic, for the potential effect on INR and increased risk of bleeding while on any antibiotic

Exclusion Criteria:

• Patient age less than 18
• Hypersensitivity to the antibiotics
• Pregnancy or breast feeding
• Patients who cannot consent for themselves
• End stage renal disease defined as creatinine clearance <30 mL/min or on hemodialysis.
• Patients who have taken antibiotics in the past 30 days
• Laxatives, stool softeners, or bulk fiber in the last 7 days
• Enemas or suppositories in the last 3 daysⱡ