The U.S. Food and Drug Administration recommended that the trial be designed to show the drug was effective over two to three months.

The FDA also made a preliminary recommendation to include a black-box warning -- signifying serious or life-threatening risks -- related to supine hypertension.

Chelsea said it would request a meeting with the FDA to address the agency's recommendations. In February, FDA staff had advised against approval of Northera, citing safety concerns.

The drug, known generically as droxidopa, is designed for symptomatic neurogenic orthostatic hypotension -- a chronic and often debilitating drop in blood pressure on standing up that is most often associated with Parkinson's disease.

Northera has an orphan status, which is granted by the regulator to drugs that treat a rare condition affecting less than 200,000 Americans and guarantees a marketing exclusivity of seven years in the country.

The drug, in use in Japan since 1989, has shown some post-marketing safety issues and is being tested in an ongoing trial. Results from this study are expected in the third quarter of 2012.

Shares of the Charlotte, North Carolina-based biopharmaceutical company closed down 3.4 percent at $3.67 on Wednesday on the Nasdaq.

(Reporting by Balaji Sridharan and Abhiram Nandakumar in Bangalore; Editing by Steve Orlofsky)

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