Danish drugmaker Novo Nordisk , the world's biggest insulin maker, said on Friday that U.S. health regulators had extended their review of its new ultra-long-acting insulin Tresiba, or degludec, to consider further data.

The unexpected delay is a disappointment since degludec is a pivotal new product with which Novo hopes to consolidate its position in the fast-growing diabetes market.

A decision on the medicines is now expected on Oct. 29, when the verdict will also be delivered on a related combination production called Ryzodeg, or degludecplus. Both drugs are designed to treat type 1 and type 2 diabetes.

The U.S. Food and Drug Administration asked for further data clarification and analyses, and the company has submitted a substantial amount of additional data.

"Due to the size and timing of these submissions the FDA considers them as major amendments to the (new drug applications)," the company said in a statement, adding that the agency had not requested additional clinical trials.

Analysts at Danske Bank said that a U.S. launch in 2012 now seemed unlikely but they did not believe the likelihood of approval had declined, so the delay should not have a big impact on valuation.

Tim Race of Deutsche Bank said the news would inevitably dampen sentiment towards Novo's highly rated shares, which trade on 22.5 times expected 2012 earnings, but he agreed the financial implications were limited.

"We see the delay as unexpected and disappointing, but ultimately not unusual," Race said in a research note.

Tresiba and Ryzodeg are seen as strong new competitors in the long-acting, or basal, insulin market, which has long been dominated by Sanofi's Lantus. Competition is hotting up in the space, with Eli Lilly also having a promising new contender in development.

Novo Nordisk has also filed for approval of the two products with the European Medicines Agency and regulators in Japan, Canada, Switzerland and some other countries.

It first filed for approval in the United States in September last year.