Salix Pharmaceuticals' antibiotic Xifaxan has failed to win favour with the US Food and Drug Administration for the treatment of irritable bowel syndrome.

As expected, the regulator has turned down the drugmaker's supplemental new drug application seeking to market Xifaxan (rifaximin) 550 mg tablets for the treatment of non-constipation irritable bowel syndrome and IBS-related bloating.

There were hopes that the Xifaxan might become a new option for patients with the condition, given that two pivotal Phase III trials of the drug showed that it induced a statistically significant improvement for the adequate relief of global IBS symptoms, IBS–related bloating, abdominal pain and stool consistency following completion of a 14–day course of therapy.

But a complete response letter from the FDA confirmed that the regulator does indeed need further information on retreatment with the drug before it can consider issuing an approval, as indicated by the company last month.

Salix said it has requested a meeting with the regulator to discuss the next steps, which should take place within 30 days.

Xifaxan was first given a US green light for travellers' diarrhoea back in 2004, but won additional approval for overt hepatic encephalopathy, a disorder caused by chronic liver failure, last year, bolstering its sales potential.