AbbVie, the North Chicago, Illinois-based maker of the top- selling arthritis drug Humira, made a fourth offer yesterday to buy Shire Plc for 30.1 billion pounds ($51.6 billion). The offer values the Dublin-based company 48 percent higher than before AbbVie first approached Shire in May. "I definitely don't think it's enough to get the deal done," Vamil Divan, a New York-based analyst at Credit Suisse, said in a telephone interview. Shire's foreign tax domicile is "a critical component that gives them a little more power."