The diabetes drug that people are counting on at Amylin Pharmaceuticals (Nasdaq: AMLN), Eli Lilly, and Alkermes (Nasdaq: ALKS) has passed a crucial test that the FDA demanded almost 10 months ago.

San Diego-based Amylin, along with its partners, said today that exenatide once-weekly (Bydureon) didn't appear to cause an irregular heart rhythm, known as QT prolongation, when it was studied in healthy individuals at both normal, and higher-than-normal doses. The study compared 75 people who were randomly assigned to get the new drug, or a placebo. Full study details weren't released in today's statement, but the companies said they plan to present the data at a future medical meeting, and submit the results for publication.

Investors and researchers are watching this study carefully because this drug seeks to replace a twice-daily injection with a once-weekly shot -- raising the potential of a more convenient medicine for patients, and a steadier way to control blood sugar in people's daily lives. Amylin shares jumped 10 percent in after-hours trading after the announcement.

"The findings of this thorough QT study are clear. Exenatide did not lead to QT prolongation, even at very high concentrations in the blood," Christian Weyer, Amylin's senior vice president of R&D, said in a statement. "This study was designed in accordance with existing guidelines and in consultation with the FDA. We are confident in these results and will continue to work toward making Bydureon available to patients in the U.S. as soon as possible."

The FDA delayed the original application for approval of Bydureon last October, when it asked the companies for more data on the drug's effect on QT prolongation. The new data will be packaged together and shipped off to the FDA for review sometime before the end of September, the companies said. Amylin has the most at stake in the FDA's decision, since it only has two other approved products and the new drug is supposed to be its major profit driver for the future. But Waltham, MA-based Alkermes, the company with technology that makes the diabetes drug last long enough in the blood to enable once-weekly injections, also has a lot at stake. Alkermes stands to collect an 8 percent royalty on worldwide sales of the drug, without having to pay expenses for marketing or manufacturing.

The market clearly has potential to be lucrative for all the companies. Demand for new diabetes treatments is surging as an estimated 25 million people in the U.S. suffer from the disease, and incidence is expected to climb for years as more people develop complications from obesity. Jefferies & Co. analyst Thomas Wei forecasted, in a June 27 note to clients, that the drug has potential to generate U.S. sales of about $2.38 billion in 2016. The product was cleared for sale in Europe by regulators there last month.

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Luke Timmerman is the National Biotech Editor of Xconomy, and the Editor of Xconomy Seattle. Email him at [email protected] or follow him on Twitter at twitter.com/ldtimmerman.