By Deena Beasley

SAN DIEGO (Reuters) - Analysis of an earlier trial found a "clinically insignificant" link between changes in heart rhythms and use of Bydureon, a long-acting diabetes drug being developed by Amylin Pharmaceuticals, Eli Lilly and Alkermes.

Amylin also said an earlier version of the drug, Byetta, was associated with a lower risk of heart failure and its shares rose nearly 6 percent.

Last October, U.S. regulators asked for more data on potential heart risks before approving the experimental medicine as a treatment for Type 2 diabetes.

Another trial is under way specifically to measure the drug's effect on the QT interval, the time the heart's electrical system takes to recharge after each beat.

Amylin has not said when those results are expected, but the company does plan to resubmit Bydureon to the Food and Drug Administration in the second half of this year, said Chris Weyer, the company's research and development head.

Meanwhile, data presented here this weekend at a meeting of the American Diabetes Association showed no significant correlation between changes in the heart-rate adjusted QT interval and treatment with Bydureon for 148 patients in an earlier trial, called Duration-1.

Amylin called the link in the earlier trial "clinically insignificant." It said that after 14 weeks the change was 1.7 milliseconds, rising to 3 milliseconds after 30 weeks of treatment with Bydureon, which is given once a week by injection.

The company also said there was no link between change in the QT interval and blood-stream levels of the drug or kidney function.

Bydureon is a longer-acting version of Byetta, known generically as exenatide, which is also sold by Lilly and Amylin. Both drugs belong to a relatively new GLP-1 class of drugs that stimulate insulin release when glucose levels become too high.

Amylin said a retrospective analysis of more than 778,000 patients found that, across all therapies, patients receiving Byetta were 54 percent less likely to develop heart failure than patients not receiving the drug.

More than 220 million people worldwide suffer from diabetes, including nearly 26 million Americans. They run a high risk of heart disease, stroke, kidney failure, blindness and limb loss.

Earlier this week, European health regulators approved Bydureon as a treatment for Type 2 diabetes.

It competes with Novo Nordisk's Victoza, a GLP-1 agonist which is injected daily. Results from a study earlier this year showed Bydureon did not control blood sugar as well as Victoza.

Amylin, Lilly and Alkermes are also studying a once-monthly suspension formulation of exenatide.

The companies said that a Phase 2 trial found that after 20 weeks, patients receiving once-monthly exenatide improved A1C levels (a measure of average blood sugar over three months) by 1.3 percentage points for the 5 mg and 8mg dose and 1.5 percentage points for the 11 mg dose.

Fifty percent of those treated with the 50 mg dose, 57 percent treated with the 8 mg dose and 70 percent treated with the 11 mg dose achieved target glucose levels.

Amylin said the results were comparable to those seen in patients treated with Bydureon.

The most common side effects associated with the once-monthly drug were headache and nausea.

Amylin's Weyer said the results were "very reassuring" but would not comment on when or if the company would conduct a pivotal trial of the once-monthly formulation.

Lilly and Amylin are fighting a legal battle over marketing of another drug, Tradjenta, or linaglipton, that was developed by Lilly and German drugmaker Boehringer Ingelheim.

Bydureon sales for Amylin are expected to reach $1.1 billion a year by 2015, according to analysts polled by Thomson Pharma.

Amylin shares rose 5.6 percent to $12.50 in after hours trading, from their closing price on Friday of $11.83 on the Nasdaq.

(Reporting by Deena Beasley, editing by Matthew Lewis and Sofina Mirza-Reid)