A new irritable bowel syndrome drug is set to hit the US market after regulators gave the green light to Amitiza, developed by Sucampo Pharmaceuticals and co-marketed with Takeda.

The US Food and Drug Administration has approved Amitiza (lubiprostone) for the treatment of IBS with constipation (IBS-C) in adult women aged 18 and over, making it the only such-approved drug in the country. The approval is based on two studies involving 1,154 patients diagnosed with IBS-C, and around 92% of them were women. More patients treated with Amitiza reported that their IBS symptoms were moderately or significantly relieved over a 12-week treatment period than those who received placebo.

The safety of long-term treatment was assessed in a study in which all patients were treated with Amitiza for a duration that ranged nine to 13 months, according to the FDA. Julie Beitz at the agency’s Center for Drug Evaluation and Research said that “this drug represents an important step in helping to provide medical relief” from the symptoms of IBS.

Given the make-up of the study, however, Amitiza has not been approved for men, because its efficacy was not conclusively demonstrated, the FDA said. Amitiza is already approved for the treatment of chronic idiopathic constipation at 24 micrograms twice a day, much higher than the 8 micrograms twice a day recommended for treatment of IBS-C.

The approval has triggered a development milestone payment of $50 million to Sucampo from Takeda. The IBS market has opened up since the FDA asked Novartis to suspend marketing of Zelnorm/Zelmac (tegaserod) in April last year, following fears that the Swiss firm’s treatment could be linked to heart attacks and strokes.

The news came just as Takeda said that its recently-announced $8.8 billion acquisition of the USA’s Millennium Pharmaceuticals has cleared all regulatory hurdles. The deal has passed the required antitrust waiting periods of the US Federal Trade Commission, the Austrian Federal Competition Authority and the German Federal Cartel Office.