“The agreed upon valuation is no longer supported as a result of the changes to the tax rules and we did not believe it was in the best interests of our stockholders to proceed,” AbbVie Chief Executive Richard Gonzalez said in a statement. Abbvie said its offer for Shire would not lapse and that it must convene a shareholder meeting before Dec. 14 to vote on the deal. Shire stands to be paid a break-up fee of about $1.64 billion if Abbvie’s shareholders vote against the deal. Chicago-based AbbVie had previously been eager to buy Shire, partly due to the opportunity to reduce its U.S.