Antibioticos

editorials

Antibiotic Therapy for the Irritable Bowel Syndrome
Jan Tack, M.D., Ph.D. The irritable bowel syndrome (IBS) is one of the most common conditions seen in clinical practice. The numberof effective pharmacologic agents for IBS is limited, and therapeutic innovation is hampered by a lack of complete understanding of the pathophysiology of the syndrome, which is probablyheterogeneous.1 Alterations in the bacterial flora are increasingly considered to be a relevant pathogenetic factor.2 Consequently, probiotics are being studied as treatment for IBS, but the magnitude ofimprovement in symptoms with probiotics is limited.2 Some studies have suggested that there are beneficial effects with poorly absorbed antibiotics, but the results of the studies have been questioned becauseof issues with patient selection, the choice of end point, and the statistical analysis, and, most of all, because lactulose breath test results were interpreted as indicative of smallintestinebacterial overgrowth.3-6 In this issue of the Journal, Pimentel et al. report the results of two identically designed, large, double-blind, placebo-controlled trials (TARGET 1 and TARGET 2) of rifaximin, apoorly absorbed antibiotic, in patients with IBS without constipation.7 A total of 1260 patients were randomly assigned to receive rifaximin, at a dose of 550 mg three times daily, or placebo for 2weeks, followed by a 10-week posttreatment follow-up period. The primary end point was the proportion of patients who reported adequate relief of IBS symptoms, as assessed by responses (yes or no) to aquestion about relief of symptoms that was asked weekly during the first 4 weeks after treatment. The key secondary end point was the proportion of patients reporting adequate relief of bloatingduring the same period. In both studies, patients consistently met the criteria for relief of global IBS symptoms and IBS-related bloating. In the rifaximin groups, as compared with the placebo groups, a...