Political furor over the recent spate of tax inversions is having little influence on how the government chooses its partners.
The Illinois company says it is keeping the US as its home base, which means no inversion benefit.
The deal includes a $1.6-billion fee if AbbVie tries to walk away.
Shire and AbbVie's courtship has entered round five. A deal would offer AbbVie tax relief, and possibly make it an acquisition target.
Abbott and Mylan are setting up a generics business. The all-stock deal will give some branded generics a new home and offer Abbott a tax benefit that will increase over time.
Salix Pharmaceuticals joins the tax-inversion migration by purchasing Cosmo Technologies.