NEW YORK (Reuters) - Amylin Pharmaceuticals Inc (AMLN.O: Quote, Profile, Research) reported a wider quarterly loss on Monday, hurt by higher expenses and lower-than-expected sales of the diabetes drug Byetta, sending its shares down more than 7 percent.

Amylin, a San Diego-based biotechnology company, posted a first-quarter net loss of $68.8 million, or 51 cents per share, compared with a loss of $49.4 million, or 38 cents per share, a year earlier.

Analysts on average expected a loss of 47 cents, according to Reuters Estimates.

Revenue rose 15 percent to $197.2 million. Net product sales of Byetta, which it co-markets with Eli Lilly and Co (LLY.N: Quote, Profile, Research), rose 8 percent to $158.5 million. The company blamed disappointing Byetta sales partly on buying patterns of wholesalers.

Robert W. Baird analyst Thomas Russo said Byetta sales "missed by a wide margin" his estimate of $181.3 million.

"While investors were expecting a wholesaler inventory reduction to negatively affect (first-quarter) reported revenues, language in the press release suggests this may have had a greater negative impact than expected," Russo said in a research note. "We feel it is unlikely to fully explain the shortfall versus expectations, however."

Sales, general and administrative expenses rose 12 percent to $98.2 million, reflecting promotional spending for Byetta and other products.

Research and development spending rose 30 percent to $77.2 million as the company invested in its program to develop a once-weekly version of exenatide, which is the generic name of Byetta. Byetta is administered twice a day.

Amylin shares fell $2.35, or 7.5 percent, to $29.06 in morning trading on the New York Stock Exchange.

(Reporting by Martinne Geller and Lewis Krauskopf; Editing by John Wallace and Maureen Bavdek)