Alexion Announces Two-For-One Stock Split

Alexion Pharmaceuticals, Inc. (Nasdaq: ALXN) announced today that its Board of Directors has approved a two-for-one stock split, payable in the form of a 100 percent stock dividend.

The stock split is subject to approval by Alexion stockholders of an amendment to Alexion’s certificate of incorporation to increase the number of authorized shares of common stock from 145 million to 290 million, which will be acted upon at Alexion’s Annual Meeting of Stockholders on May 11, 2011. If the certificate of incorporation is amended, the stock split will be effected and stockholders will receive one additional share of common stock for every share they own as of the close of business on May 2, 2011. The additional shares are expected to be distributed on or about May 20, 2011. As of February 11, 2011 the Company had approximately 91.3 million shares of common stock outstanding.

Separately, Alexion announced that it has been included in the NASDAQ-100 Index, effective April 4, 2011, prior to market open. The NASDAQ-100 Index includes 100 of the largest domestic and international non-financial companies listed on The Nasdaq Stock Market based on market capitalization.

About Alexion

Alexion Pharmaceuticals, Inc. is a biopharmaceutical company working to develop and deliver life-changing drug therapies for patients with serious and life-threatening medical conditions. Alexion is engaged in the discovery, development and commercialization of therapeutic products aimed at treating patients with a wide array of severe disease states, including hematologic and kidney diseases, neurologic disorders, ophthalmic, transplant, other inflammatory disorders, and cancer. Soliris® (eculizumab), Alexion's first marketed product, is approved in more than 35 countries as a therapy for patients with PNH, a debilitating and ultra-rare life-threatening blood disorder. Alexion is evaluating other potential indications for Soliris and is pursuing development of other innovative biotechnology product candidates in early stages of development. This press release and further information about Alexion Pharmaceuticals, Inc. can be found at: www.alexionpharma.com.

Proxy Statement

In connection with the 2011 Annual Meeting of Stockholders, Alexion will file a proxy statement with the Securities and Exchange Commission, or SEC. Stockholders are advised to read the definitive proxy statement carefully and in its entirety when it becomes available because it will contain important information about the proposals to be presented and voted upon. Stockholders may obtain a copy of the definitive proxy statement when available and any other relevant documents filed by Alexion for free at the SEC web site at www.sec.gov. The definitive proxy statement and other documents also may be obtained when available for free from Alexion Pharmaceuticals, Inc., 352 Knotter Drive, Cheshire, Connecticut 06410.

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