By Deena Beasley and Vidya L. Nathan

The U.S. Food and Drug Administration on Friday approved Danish drugmaker Novo Nordisk's diabetes drug Tresiba, two years after rejecting the long-acting form of insulin.

The agency also approved the company's Ryzodeg, an injection that combines Tresiba and a fast-acting man-made form of insulin. Novo Nordisk is the world's No. 1 maker of insulin, a hormone normally produced by the pancreas that helps the body use glucose for energy.

Tresiba is already being sold in 30 countries, and analysts expect annual sales of $2.4 billion by 2020, according to Thomson Reuters Cortellis.

"The U.S. market for basal insulin represents over 80 percent of the global market," said Soren Lontoft Hansen, senior analyst at brokerage firm Sydbank. "We expect a positive price reaction on Monday between 5 percent and 10 percent."

The FDA had declined to approve Tresiba in 2013, asking for more data on risks of heart problems from using the drug. 

U.S.-listed shares of Novo Nordisk fell 10 cents to close at $54.93 on Friday.

Hansen said the U.S. approval sets the stage for Novo Nordisk to compete against long-acting insulins Lantus and Toujeo sold by rival Sanofi SA.

Todd Hobbs, chief medical officer for Novo Nordisk in North America, said diabetics using Tresiba can go as long as 42 hours between doses, compared with 18 to 24 hours for Levemir, the company's current long-lasting insulin.

As an ultra-long acting product, Tresiba is sold at a premium to other insulins, but Novo Nordisk said the company has not yet determined a U.S. price for the new insulin.

"We want to do everything we can to make it as affordable and as broad of an access as we can," Hobbs said.

Novo Nordisk said it expects to launch Tresiba in the United States during the first quarter of 2016. A company spokesman said a launch target for Ryzodeg has not yet been determined.

Analysts were confident that the FDA would approve the drug after Novo Nordisk submitted interim test results to the agency earlier this year. The ongoing cardiovascular outcomes trial will likely conclude in mid-2016, Hobbs said.

Friday's FDA approvals include warnings that Tresiba and Ryzodeg should not be used by patients who have high levels of the chemical ketone.

Novo Nordisk earlier on Friday said its new experimental once-weekly diabetes drug, semaglutide, was successful in a late-stage study.

(Additional reporting by Ole Mikkelsen in Copenhagen; Editing by Sriraj Kalluvila and Bill Rigby)