Food and Drug Administration regulators have told MannKind Corp. they need another four weeks to decide whether to approve the company’s experimental inhaled insulin treatment for sale.

The Valencia biotech’s announcement on Monday came in advance of an FDA deadline to report to the company by Wednesday on its progress in reviewing the drug Afrezza. That the agency did not reject the drug outright was seen as a positive by some investors, spiking the company’s stock up by nearly 12 percent before retreating by midday Tuesday.

MannKind has been waiting nearly a year for a decision after the FDA requested more safety study information from the company. Regulators were expected to be cautious about approving Afrezza because rival Pfizer had pulled its inhaled insulin Exubera off the market in 2007 in part for safety reasons.

In addition, MannKind faces a lawsuit filed in October by its former senior director for regulatory affairs, alleging that the company withheld from the FDA information about possible “scientific misconduct” at clinical study clinics in Russia and Bulgaria. MannKind has said the charges are “without merit.”

Shares at midday were up 18 cents, or 2.3 percent, to $8.15 on the Nasdaq.