AbbVie Inc. and Shire Plc’s management are in active talks about a potential takeover of Shire, which AbbVie has offered to acquire for about $51.5 billion, people with knowledge of the matter said.

AbbVie Chief Executive Officer Richard Gonzalez is in New York with officials from Shire for the discussions, which are at an early stage, the people said, asking not to be identified discussing a private matter. The talks may not lead to an agreement, the people said.

AbbVie made a fourth offer to buy Shire on July 8, valuing the Dublin-based company’s shares at 51.15 pounds each, or about 30.1 billion ($51.5 billion) in total. Shire hasn’t made any formal response to the offer.

Stephanie Fagan, a Shire spokeswoman, said she wasn’t immediately able to comment. Adelle Infante, a spokeswoman for AbbVie, didn’t immediately have a comment.