* US panel to consider diabetes drug on Thursday
* Novo shares fall 4.8 percent
* Company says benefits for diabetics outweigh risks (Adds details on safety data; updates shares)
WASHINGTON, March 31 (Reuters) - U.S. regulators want outside advisers to assess heart risks from Novo Nordisk's (NOVOb.CO) proposed diabetes drug, liraglutide, as well as thyroid tumors in rodents, documents released on Tuesday said.
Few major cardiovascular problems were seen in studies of liraglutide, but the small numbers limited the analysis of the drug's safety, Food and Drug Administration reviewers said.
The shares of the Danish company fell 4.8 percent in trading in Copenhagen. Analysts view the drug as a potential blockbuster and key driver for Novo in the coming years.
Cardiac risks have emerged as a major concern with diabetes drugs and the FDA has asked makers to analyze if the medicines raise the chances of heart attacks, strokes or other problems.
Some comparisons suggested liraglutide carried a higher cardiovascular risk than a placebo, depending upon how the data were analyzed, FDA reviewers said. Tests against other drugs, however, showed similar heart risks.
Studies in rats and mice given liraglutide found cases of thryoid tumors and the FDA will ask the panel if that concern applies to humans.
Five people treated with the drug developed a type of thyroid tumor compared with one given a different diabetes drug. Thyroid tumors are common in the general population and the ones seen in liraglutide patients were "very small," the FDA reviewers said.
"The applicability of these rat and mouse findings to humans in not fully understood."
An FDA advisory panel of outside experts will review liraglutide on Thursday and vote on whether there is enough data on the heart and tumor issues to recommend approval. The proposed brand name is Victoza.
The FDA's own staff reviewers said liraglutide was effective at lowering blood sugar and in some cases worked better than other medicines.
Novo Nordisk, in a separate summary prepared for the panel, said liraglutide offered advantages that included weight loss and once-a-day dosing unrelated to meals.
The company said the thyroid tumors were "rodent-specific" and there was no sign they would occur in humans. Novo proposed a large, post-approval study to further assess heart-related risks.
Overall, the drug has a "favorable benefit/risk profile," Novo said.
Liraglutide belongs to the GLP-1 class of injectable drugs that stimulate insulin release when glucose levels become too high. If approved, it would provide competition for Amylin Pharmaceuticals Inc's AMLN.O GLP-1 drug Byetta.
The FDA usually approves drugs that win endorsements from its independent advisory panels, although the agency has rejected or delayed some medicines recently recommended by outside advisers. (Editing by Dave Zimmerman and Andre Grenon)