Chicago-based AbbVie, which makes top-selling arthritis drug Humira, is eager to buy Shire to reduce its U.S. AbbVie’s said its board plans to meet on Oct. 20 to consider whether to withdraw or modify its recommendation on the deal with Shire. Under British takeover rules, AbbVie has until July 18 to announce a firm offer for Shire, extend the deadline for an offer, or walk away. Dublin-based Shire sells drugs for rare diseases.