Biotechnology company Biogen Idec Inc. (Nasdaq: BIIB) said its board authorized a $3 billion buyback of about 57 million shares on Wednesday, sending shares more than 5 percent.

The company’s stock gained $2.57, or 5.22 percent to reach $51.76 in morning trading on the New York Stock Exchange.

The repurchase amount represents about 16 percent of the company's 343.2 million common shares outstanding.

Following this transaction, Biogen Idec will maintain the capacity to pursue substantial and attractively valued external growth opportunities, said James C. Mullen, chief executive.

Shareholders will be able to tender some or all of their shares for between $47 and $53 per share.

If completed, the stock repurchase will be funded through a combination of up to $1.5 billion cash and up to $1.5 billion of debt.