Shares in MannKind Corp are sure to sink when the markets open later today in the USA on the news that the Food and Drug Administration have again rejected the firm's inhaled insulin Afrezza.

The FDA has issued a second complete response letter for Afrezza for the treatment of adults with type 1 and type 2 diabetes, having already rejected the therapy in March. The agency has requested that MannKind conduct two clinical trials with its next-generation Dreamboat inhaler (one in patients with type 1 diabetes and the other type 2 diabetes), with at least one trial including a treatment group using the first-generation MedTone inhaler "in order to obtain a head-to-head comparison of the data for the two devices". 

The FDA also wants more information concerning "the performance characteristics, usage, handling, shipment and storage of the next-generation device", plus an update of safety information related to Afrezza as well as details on proposed user training. It also has questions about changes to the labelling of the device, blister pack, foil wrap and cartons.

Quite a list but MannKind does not sound too disheartened. Chief executive Alfred Mann noted that the firm has already begun a series of studies of the next-generation device and "we plan to meet with the agency as quickly as possible in order to be confident that these trials, with appropriate modifications to incorporate a comparison to the MedTone device, will suffice".

He added that "while we are disappointed with the complete response letter, we are encouraged that the FDA is asking for clinical studies only to confirm the bridging and handling of the next-generation device in order to compare it to the device used in our extensive clinical programme". Mr Mann concluded by saying that "we remain committed to working with the FDA to make Afrezza available to people with diabetes".

Investors seem less committed, however, and MannKind shares fell 4% to $5.15 in after-hours trading, having been suspended earlier pending the FDA's decision.