NEW YORK (AP) — Shares of Amylin Pharmaceuticals Inc. surged more than 54 percent Wednesday on a report the diabetes drug maker recently turned down a buyout offer from Bristol-Myers Squibb Co. worth $3.5 billion.

Bloomberg News reported that Bristol-Myers proposed to buy Amylin for $22 per share. It said there have been no talks between the companies since the initial offer earlier this year. Bristol-Myers Squibb and Amylin declined to comment on the story, which cited anonymous sources.

Amylin shares rose $8.38, or 54.5 percent, to close at $23.77. Earlier the shares peaked at $24.09, their highest price since August 2008.

In February Bristol-Myers bought hepatitis C drugmaker Inhibitex for $2.5 billion. The New York company’s biggest sellers include the oral diabetes treatment Onglyza, and the psychiatric drug Abilify. Bristol-Myers markets blood thinner Plavix through a partnership with French drugmaker Sanofi, and while Plavix is the second-best selling drug in the world, it will lose U.S. patent protection in May. Its 2011 revenue amounted to $21.24 billion, compared with Amylin’s revenue of $650.7 million.

Bristol-Myer’s shares ended unchanged at $33.67.

Amylin makes the twice-a-day diabetes drug Byetta and a newer once-a-week version called Bydureon. Both drugs were marketed through a partnership with Eli Lilly and Co., but the companies announced in November that they were ending their partnership. Amylin is taking over marketing both products outside the U.S., and it has been looking for a new partner to help sell the drugs.

Amylin also makes a diabetes drug called Symlin.