SAN DIEGO (AP) — Amylin Pharmaceuticals Inc. said Tuesday its third-quarter loss narrowed as lower research and development costs offset a decline in sales of the diabetes treatment Byetta. Amylin lost $26.7 million, or 19 cents per share, in the quarter ended in September, compared with a loss of $79 million, or 58 cents per share, during the same period a year prior. Revenue fell 3 percent to $211.2 million from $218.4 million. Analysts polled by Thomson Reuters expected a wider loss of 29 cents per share on slightly higher revenue of $219 million. The company's expenses fell 16 percent to $233.6 million as recently completed clinical trials drove lower research and development costs. Sales of Byetta, Amylin's key revenue driver, fell 5 percent to $171.1 million. Sales of the diabetes treatment Symlin rose slightly to $21.8 million. Eli Lilly & Co. is Amylin's partner on the twice-daily injectable Byetta. The companies are developing a new version, called exenatide LAR, that is a once-weekly injection. A third partner, Alkermes Inc., is contributing the long-acting technology. Shares of Amylin fell 35 cents to close at $13.14.