Salix announced top-line results from its Phase 3 TARGET 3 clinical trial evaluating rifaximin 500mg in patients with irritable bowel syndrome with diarrhea (IBS-D), who respond to an initial treatment course with rifaximin 500mg TID (three times daily) for 14 days.

TARGET 3 is a randomized, double-blind, placebo-controlled study designed to investigate the efficacy and safety of repeat treatment with rifaximin 550mg TID for 14 days. The effects of rifaximin on the gut microbiota were evaluated by two methods: traditional culture techniques and next-generation gene sequencing of stool samples collected from approximately 100 randomly selected patients in the trial. Skin swabs were also obtained from an additional 113 randomly selected patients and cultured for Staphylococcus bacteria.

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The data revealed no disturbance of fecal microbiota in patients taking repeat courses of rifaximin compared to patients taking a single course of rifaximin followed by placebo for the remainder of the trial. Results of the culture and susceptibility testing demonstrate no evidence of cross-resistance to non-rifamycin antibiotics in isolates grown from either stool or skin swab cultures. Also repeat treatment courses of rifaximin do not appear to predispose patients to the emergence of potentially pathogenic bacteria (eg, C. difficile, Enterococcus, or Staphylococcus) in the stool or on the skin. Transient changes in the rifaximin minimum inhibitory concentrations (MICs) were observed in some of the normal flora but these changes were reversible over time. A very small number of C. difficile isolates were identified in stool samples at a rate consistent with literature reports of asymptomatic carriers in the general population, and none of these isolates demonstrated rifaximin resistance.

Xifaxan (rifaximin) 550mg is already approved for the reduction in risk of overt hepatic encephalopathy recurrence.

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