Regeneron Pharmaceuticals Inc said U.S. regulators have denied approval for it to expand use of its Arcalyst drug to prevent gout flares, asking that the company provide more clinical data.

The rejection follows a unanimous vote against the drug's approval in early May by advisors to the U.S. Food and Drug Administration, with panel members expressing concern that the company had only done a 16-week study.

The agency has requested additional clinical data, including chemistry, manufacturing and controls information related to a proposed new dosage form for the injectable drug, Arcalyst, Regeneron said in a statement.

Regeneron, which had pitched Arcalyst for approval to treat gout flares in patients starting uric acid-lowering therapy, said it was reviewing the FDA's requests.

Patients afflicted with gout experience severe pain and inflammation due to deposits of uric acid -- a body waste product -- in the joints and soft tissues.

Known generically as rilonacept, Arcalyst is already on the market to treat a group of rare genetic auto-inflammatory diseases. It only contributes modestly to Regeneron's overall sales.

Regeneron is better known for its recently approved Eylea to treat macular degeneration, the leading cause of blindness in the elderly. Arcalyst brought in sales of $6 million in the April-June period, while Eylea's sales shot up 57 percent to $194 million.

New York-based Regeneron's shares closed at $135.47 on Monday on the Nasdaq.