Drugmaker AbbVie is raising its takeover offer for Irish pharmaceutical company Shire for a fourth time as it attempts to secure a tax inversion deal. Under the new offer, AbbVie raised its cash-and-stock bid by 11% to $51.6 billion. Shire already rejected AbbVie's previous bid of $46 billion, saying it significantly undervalued the company. As part of the deal, AbbVie would acquire Shire and move the combined company's tax home to the U.K., which has a main corporate tax rate of 21%, below the U.S. federal corporate tax rate of 35%. Shire did not immediately reject the offer, saying its board would meet to consider the proposal.

More from Video

Investors Shouldn't Be Worried About Trump's Trade Tariffs: Ian Bremmer

Investors Shouldn't Be Worried About Trump's Trade Tariffs: Ian Bremmer

Abercrombie & Fitch CEO Reveals to TheStreet How She Is Turning Company Around

Abercrombie & Fitch CEO Reveals to TheStreet How She Is Turning Company Around

The Chart Professor: Worried About United Technologies Right Here

The Chart Professor: Worried About United Technologies Right Here

Veteran Foreign Affairs Expert Ian Bremmer Reveals How to Price Political Risk

Veteran Foreign Affairs Expert Ian Bremmer Reveals How to Price Political Risk

Jim Cramer: I've Liked Six Flags Entertainment Stock as an Income Producer

Jim Cramer: I've Liked Six Flags Entertainment Stock as an Income Producer