The FDA has indicated that, before the antibiotic drug rifaximin (Xifaxan) can be approved for treating irritable bowel syndrome (IBS), its manufacturer must provide data on how the agent should be used in retreating patients with recurrent symptoms, the company said.
Salix Pharmaceuticals, of Raleigh, N.C., said it has received a complete response letter from the FDA turning down its application to market rifaximin and noting what the company called "a newly expressed need for retreatment information."
The company announced two weeks ago that it believed approval was unlikely, following a telephone conversation with FDA officials.
Rifaximin, a broad-spectrum antibiotic with negligible systemic availability after oral administration, is currently approved for treating "traveler's diarrhea" associated with E. coli infection and also to reduce the risk of hepatic encephalopathy.
Two clinical trials reported earlier this year indicated that the drug was modestly more effective than placebo in treating bloating and nonconstipational symptoms in IBS without major adverse effects.
About half of patients receiving the drug obtained "adequate relief" of symptoms after a two-week course of treatment, compared with some 40% of the trials' placebo groups.
However, about 25% of patients responding to rifaximin initially were no longer reporting adequate relief 10 weeks after completing treatment.
The drug's efficacy and safety in retreatment was not addressed in these or other trials for the IBS indication.
Salix said it would request a meeting with FDA officials to discuss how it should proceed.