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For further information, see CMDT Part 15-27: Malabsorption

Key Features

  • Overgrowth of bacteria in normally sterile segments of small bowel; may result in malabsorption of fat with steatorrhea

  • Causes include

    • Gastric achlorhydria

    • Anatomic abnormalities of the small intestine with stagnation (afferent limb of Billroth II gastrojejunostomy, resection of ileocecal valve, small intestine diverticula, obstruction, blind loop)

    • Small intestine motility disorders (vagotomy, scleroderma, diabetic enteropathy, chronic intestinal pseudo-obstruction)

    • Gastrocolic or coloenteric fistula (Crohn disease, malignancy, surgical resection)

    • Miscellaneous disorders

Clinical Findings

  • Many patients are asymptomatic

  • Bloating, flatulence, abdominal pain, diarrhea, and sometimes steatorrhea with weight loss

  • May also be present in a subset of patients with irritable bowel syndrome

  • Severe cases may result in clinically significant vitamin and mineral deficiencies, including

    • Fat-soluble vitamins A or D

    • Vitamin B12

    • Iron


  • Noninvasive breath hydrogen and methane tests with glucose or lactulose as substrates are generally preferred because of their ease of use

  • Following ingestion of glucose 75 g or lactulose 10 g,

    • A rise in exhaled breath hydrogen of 20 ppm or methane ≥ 10 ppm within 90 minutes suggests bacterial overgrowth

    • Has 65% diagnostic agreement with small bowel cultures

  • Small bowel CT or MR enterography or barium radiography: identifies mechanical factors predisposing to intestinal stasis

  • Small intestinal biopsy

    • Excludes other mucosal malabsorptive conditions (eg, celiac disease)

    • Detects intestinal inflammation

  • A specific diagnosis can be established firmly only by an aspirate and culture of distal duodenal secretion that demonstrates over 103 organisms/mL


  • Correct the anatomic defect when possible

  • Otherwise, treatment for 7–10 days with oral broad-spectrum antibiotics improves symptoms in up to 90% of patients for weeks to months

  • Recommended regimens include

    • Ciprofloxacin 500 mg orally twice daily

    • Norfloxacin 400 mg orally twice daily

    • Amoxicillin clavulanate 875 mg orally twice daily

    • Trimethoprim-sulfamethoxazole (one double-strength tablet) orally twice daily

    • Rifaximin 400–550 mg orally three times daily

    • A combination of neomycin 500 mg orally twice daily plus metronidazole 250 mg orally three times daily

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