The companies are trying to gain U.S. approval for the drug to treat constipation caused by opioids in patients with chronic, non-cancer pain.

The "priority review," or the expedited review granted by the U.S. Food and Drug Administration means that Amitiza's application to gain approval for this new use will now be reviewed in six months, instead of the standard ten months.

Sucampo has a partnership with Japan-based Takeda Pharmaceutical Co Ltd on Amitiza.

The drug is approved in the United States to treat chronic constipation in adults, and for irritable bowel syndrome accompanied by constipation in adult women.

The companies said they expect the FDA to deliver a decision by late January 2013.

Opioids are very effective at managing pain, but constipation is a very common side-effect.

The FDA grants priority review for treatments that aim to cure serious diseases and fill unmet medical needs.

Sucampo's shares closed at $4.53 on Tuesday on the Nasdaq. They were up 7 percent at $4.85 in extended trade and rose as high as $4.99.

(Reporting by Zeba Siddiqui in Bangalore; Editing by Sreejiraj Eluvangal)

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