X0306 4 2013-02-19 0 0001113481 MEDICINES CO /DE MDCO 0001427141 O'Connor William Bernard 8 SYLVAN WAY PARSIPPANY NJ 07054 0 1 0 0 Sr VP & Chief Acct. Officer Common Stock 2013-02-19 4 S 0 1143 31.80 D 20790 D Represents the number of shares sold to cover the tax expense associated with the vesting of restricted shares held by Mr. O'Connor pursuant to his Restricted Stock Agreements with the Company. The range of prices for the transactions reported on this line is between $31.73 and $31.88 per share. The price reported above reflects the weighted average sales price. The undersigned undertakes, upon request by the Commission staff, the issuer or a security holder of the issuer, to provide full information regarding the number of shares sold at each separate price. /s/ William B. O'Connor 2013-02-21