Shares in MannKind Corp. plunged nearly 20 percent Monday after they were downgraded by Jefferies & Co. Analyst Salveen Kochnover, who said that it is becoming unclear if there is a viable market for MannKind’s main product; an inhalable insulin treatment for diabetics.

The downgrade comes after Cambridge, Mass.-based biotech company Alkermes Inc. said that Eli Lilly and Co. plans to end its collaboration on developing an inhalable form of insulin for diabetes.

Alkermes said it expects Lilly to make a decision to discontinue the program this week and added that it is not aware of any safety, efficacy, or manufacturing issues that have arisen regarding the product, AIR Insulin, since Lilly’s last public update on the program.

Pfizer Inc. and Novo Nordisk A/S of Denmark, recently scrapped work on similar products; Pfizer said too few patients preferred inhalable insulin to its injectable form.

However, MannKind issued a statement saying they were still fully behind the devlopment and completion of the insulin product.

“The decisions of Eli Lilly and Company as well as Pfizer and Novo Nordisk to discontinue the development of their inhaled insulin products reinforce this view. None of those products offer any advantages over injectable rapid acting insulin analogs,” the company said in a statement. “By contrast, in clinical trials to date, Technosphere Insulin has shown important advantages over the treatment that is presently considered to be the most effective meal-time therapy for patients.”

This also comes less than a week after Valencia-based MannKind reported an increased fourth quarter loss. However, the loss was less than Wall Street had anticipated.

Shares were up as much as 7 percent last week but were down 19 percent to $4.43 during early trading Monday hitting a 52 week low of $4.40 during trading.