LONDON (Reuters) - The launch of the first drug to treat binge eating disorder helped Shire (>> Shire PLC) post a better-than-expected 20 percent rise in first-quarter earnings on Thursday.

Shire received approval to use Vyvanse, an amphetamine widely prescribed to treat hyperactivity, for an eating disorder only officially recognised in the United States two years ago.

Sales of Vyvanse increased by 17 percent to $417 million (£271.3 million), Shire said on Thursday.

Chief Executive Flemming Ornskov said data did not differentiate between Vyvanse used for ADHD and for Binge Eating Disorder (BED), but overall prescriptions for adults in the five to six weeks since it went on the market were up about 3 percent.

"We look at the prescription trends and take that as a great indicator for the unmet need for this condition," he said.

The decision to approve use of Vyvanse in BED shows a growing willingness by drug regulators to consider novel ways to fight eating problems.

Earlier this month, Novo Nordisk (>> Novo Nordisk A/S) also launched its injectable Saxenda obesity drug in the United States, following the recent introduction of other new weight-loss pills.

Shire said a good performance by Cinryze, a treatment for hereditary angioedema, also contributed to the 20 percent jump in post non-GAAP earnings per share of $2.84, beating a market consensus of $2.60.

"We are firing on all cylinders," Ornskov said. "We are very satisfied with the progress we've made."

Shares in Shire, which reached an all-time high of 5,755 pence earlier this month, were trading up 2.8 percent at 5,440p by 1310 London time.

Analyst Mick Cooper at Edison Investment Research said the strong first-quarter performance underlined Shire was well on track to deliver mid-single digit earnings growth for the full year, despite the currency uncertainties.

Ornskov said he was excited about U.S. regulators assigning priority review designation to lifitegrast, a new drug that analysts say could be a breakthrough in the treatment of dry eye disease.

"The designation is normally given if a compound potentially would bring significant progress either in terms of safety or efficacy, so we take that as a positive sign," he said, adding that the FDA would give a verdict on the data in October.

The Dublin-based group, which posted an 11 percent rise in revenue to $1.49 billion, also appointed Jeff Poulton as chief financial officer, a position he had filled on an interim basis since December.

(Additional reporting by Ben Hirschler; Editing by Sarah Young and David Holmes)

By Paul Sandle

Stocks treated in this article : Novo Nordisk A/S, Shire PLC