Non-absorbable antibiotics and small bowel bacterial overgrowth.

The normal gastrointestinal flora includes no more than 10(3) organisms/ml of gastric aspirate and no more than 10(5) organisms/ml of duodenal or jejunal juice. The organisms are primarily gram-positive and aerobic bacteria. In particular anatomical or functional predisposing conditions, an abnormal colonization takes place in the small bowel with microbial concentrations > or = 10(7)/ml of aspirate and with a predominance of anaerobes and coliforms. At times this small bowel bacterial overgrowth remains asymptomatic, but more often leads to a true malabsorption syndrome with symptoms, such as diarrhoea, weight loss and megaloblastic anemia. The most accurate procedure for confirming the presence of this condition is represented by the bacterological analysis of the jejunal aspirate. The routine use of this method is, however, notably hindered by the need for intubation of the patient and by the lack of laboratories suitably equipped for anaerobe culture. As an alternative to this complex procedure, numerous non-invasive tests have been perfected over the last few years, including the glucose- or lactulose- H2 breath test. The main aim of the treatment of the small bowel bacterial overgrowth is the suppression of the bacterial colonization using antimicrobial therapy. Among the local-action non-absorbable antibiotics, rifaximin, was shown to have bactericidal activity against aerobes and anaerobes bacteria, such as bacteroides, lactobacilli and clostrides. In controlled clinical trials the antibiotic has demonstrated therapeutic efficacy in bacterial origin diarrhoea, in porto-systemic encephalopathy, in diverticulosis and, finally, in small bowel bacterial overgrowth.