X0303 4 2010-01-11 0 0000899866 ALEXION PHARMACEUTICALS INC ALXN 0001457477 Hallal David C/O ALEXION PHARMACEUTICALS, INC 352 KNOTTER DRIVE CHESHIRE CT 06410 0 1 0 0 SVP Commercial Ops, Americas Common Stock, par value $.0001 per share 2010-01-11 4 S 0 1088 47.78 D 8239 D These sales were made to cover the withholding taxes immediately following the vesting of previously granted Restricted Stock. This transaction was executed in multiple trades through a broker-dealer at prices ranging from $47.47 - $47.98. The price reported in this column reflects the weighted average sales price. Upon request, the reporting person will provide to the SEC staff full information regarding the number of shares sold at each price. /s/ David Hallal 2010-01-12