MannKind Corp. announced that it won’t find a marketing partner for its inhaled insulin drug until at least 2010, sparking a sell-off of its stock.

By late morning, shares of the Valencia-based drug maker had dropped $2.57 or 26 percent to trade at $6.64.

In June, the company announced it was in talks with large pharmaceutical companies to jointly market Afresa, an inhaled alternative to injected insulin for diabetics. But the Food and Drug Administration won’t approve Afresa until at least January 2010, the next scheduled hearing for the drug.

“Since we do not expect a response from the FDA before January 2010, we believe that we will not conclude a deal before the end of 2009,” the company said in the filing Tuesday with the Securities and Exchange Commission.

Afresa is the most commercial drug in Mannkind’s portfolio. The biotech research firm continues to develop inhaled insulin even though the largest drug companies, including Pfizer, Novo Nordisk and Eli Lilly & Co. have abandoned the quest because of limited revenue potential.