Shares of Amylin Pharmaceuticals Inc rose as much as 51 percent on Wednesday after Bloomberg News reported the company rejected a $3.5 billion unsolicited takeover bid from Bristol-Myers Squibb Co.

Bristol-Myers proposed an acquisition at $22 a share in a letter to Amylin, which the board turned down last month, according to Bloomberg, which cited two people with knowledge of the matter.

Bloomberg said Bristol-Myers hasn't approached Amylin since the rejection.

Amylin's shares rose 41 percent to $21.65 in hectic early trading on Nasdaq. Earlier in the session they rose to a year-high $23.26.