Shares of MannKind Corp. fell nearly 13 percent in after-hours trading on Wednesday after the Valencia biotech said in a regulatory filing that it soon plans to sell shares of its common stock and warrants.

The Valencia biotech led by medical device billionaire Alfred Mann did not disclose the size or terms of the offering, but in August registered for a future sale of up to $500 million in common and preferred stock, warrants, and debt securities. The company has a market cap of about $485 million.

Approval for the company’s first product, the Afrezza insulin inhaler for diabetics, was delayed last year after the U.S. Food & Drug Administration asked for additional tests. MannKind recently completed enrollment of patients for those studies and expects to complete the trials and submit the data to regulators next year.

Jefferies & Co. Inc. and Piper Jaffray & Co. will manage the offering, MannKind said.

Shares earlier closed up 2 cents, or less than 1 percent, to $2.80 on the Nasdaq, but fell 13 percent in after-market trading.