UPDATE 2-US FDA issues alert on kidney problems with Byetta

* Label changes for Lilly-Amylin diabetes drug

* FDA says reports represent small percentage of patients

* Companies say cases usually complicated by other factors (Adds company comments)

NEW YORK, Nov 2 (Reuters) - Patients and doctors should be aware of possible kidney function problems with Eli Lilly (LLY.N) and Amylin Pharmaceuticals' (AMLN.O) Byetta diabetes drug, U.S. health regulators said on Monday.

The U.S. Food and Drug Administration received 78 reports of problems with kidney function in patients using Byetta from April 2005 through October 2008.

Nearly 7 million prescriptions for the drug were written during roughly the same period, so the agency noted the number of kidney problems represented a "small percentage" of the total number of patients on the drug.

Nonetheless, the FDA approved changes to Byetta's prescribing label to include information about the kidney function reports.

"Health care professionals and patients taking Byetta should pay close attention to any signs or symptoms of kidney problems," said Amy Egan, an FDA official in the agency's division of metabolism and endocrinology products.

On Friday, Lilly and Amylin won approval to market the drug as a stand-alone treatment for type 2 diabetes. Byetta previously was approved only for patients who were taking other common diabetes medications and had not achieved adequate control of blood sugar.

In a joint statement from the companies on Monday, Amylin Senior Vice President Orville Kolterman said post-approval reports of serious changes in kidney function "have been rare and usually complicated by other factors that could have contributed to the kidney problems."

He added that there was "no evidence from preclinical and clinical studies that Byetta has any direct toxic effect on the kidney" and noted that diabetes itself is the leading cause of kidney failure. (Reporting by Lewis Krauskopf and Lisa Richwine; Editing by Tim Dobbyn and Carol Bishopric)