Novo Nordisk ( NVO - Get Report), the world's largest seller of insulin products, said Wednesday that it has sued Pfizer ( PFE - Get Report) for patent infringement over the inhaled insulin Exubera.

Pfizer expects to begin a full U.S. launch of Exubera in September. Novo Nordisk is one of several companies trying to develop inhaled insulin, but it's a number of years away from seeking regulatory approval.

Novo Nordisk, based in Denmark, filed the suit in federal court in New York, alleging that Pfizer "willfully infringed" on the patents. Novo Nordisk also said it plans to seek a preliminary injunction "that would prohibit Pfizer from continuing its unlawful conduct" while the lawsuit continues.

"The patents we are asserting are for groundbreaking research on new approaches to treat diabetes," said Jim Shehan, vice president and general counsel for Novo Nordisk's U.S. unit. "As all research-based companies recognize, patent protection is necessary to safeguard the investment that biomedical research requires."

Bryant Haskins, a Pfizer spokesman, said the company hasn't had an opportunity to review the lawsuit, "but we are confident in the innovation behind the development of this important new medicine. Exubera meets a critical medical need for diabetes patients in managing a complicated, debilitating disease."

Exubera, developed with Nektar Therapeutics ( NKTR - Get Report), is a dry-powder version of insulin that's inhaled through a special device.

Novo Nordisk has been working on an inhaled insulin using technology developed by Aradigm ( ARDM). The product, known as AERx, uses a liquid form of insulin.

Assuming it reaches the market on schedule, Exubera will perhaps have a two- or three-year head start on products from other companies who are betting they can convince enough diabetics to inhale insulin rather that inject it. Analysts say the closest competitor to Exubera is a product from the team of Eli Lilly ( LLY - Get Report) and Alkermes ( ALKS).

Other companies working on inhaled insulin separately include MannKind ( MNKD) and Kos Pharmaceuticals