A once-a-week version of the diabetes drug Byetta, by Amylin Pharmaceuticals Inc. (AMLN), was better at controlling blood glucose levels and reducing weight in patients with diabetes, according to a study released Saturday.

The 26-week study, released at the annual American Diabetes Association conference, compared patients taking a weekly version of Byetta and an older diabetes drug to those taking Takeda Pharmaceutical Co.'s (4502.TO) Actos and Merck & Co.'s (MRK) Januvia in combination with an older diabetes drug.

The study said 70% of patients taking the weekly version of Byetta, referred to specifically as exenatide once weekly, had improved glucose control and loss in weight compared to about 50% in patients taking Januvia and 14% taking Actos.

A Merck spokeswoman said the company is confident physicians will continue to prescribe Januvia based on its "proven efficacy."

Representatives from Takeda weren't immediately available to comment.

A version of Byetta that is injected twice a day is already approved by the U.S. Food and Drug Administration. Amylin co-develops the drug with Eli Lilly & Co. (LLY) and Alkermes Inc. (ALKS), and is seeking FDA approval for the once-a-week version.

If approved, exenatide once weekly would be the first weekly diabetes drug and analysts predict the convenience of the medicine could push the drug to multibillion-dollar sales within several years.

The study may also help answers safety questions that have been overshadowing Byetta. The study shows none of the more than 100 patients who took the exenatide once weekly suffered from an inflamed pancreas, also known as pancreatitis. Two patients on Actos reported suffering from pancreatitis, while none did who took Januvia.

Amylin management has been under pressure from activist investor Carl Icahn and others who say the company hasn't properly handled Byetta sales. They say the drug hasn't lived up to its potential, though the once-a-week version could change that.

-By Jared A. Favole, Dow Jones Newswires; 202-862-9207; jared.favole@dowjones.com