Abbvie wants Shire and it doesn’t appear willing to take ‘no, thank you’ as a response.

The aggressive Chicago-based AbbVie slammed Shire with a fourth buyout offer on Monday, even after three previous offers received rejections from Shire’s U.S. headquarters in Wayne.

Last time AbbVie’s CEO said he wouldn’t rule out a hostile takeover; this time AbbVie put its $51.5 billion bid on the table publicly without first bringing it to Shire, according to a Philadelphia Business Journal report.

Shareholders were cautioned not to take any action until a more firm proposal materialized.

AbbVie officials, who last offered $46.5 billion, said in the PBJ article that the merger “would create a larger and more diversified biopharmaceutical company with multiple leading franchises and significant financial capacity for future acquisitions and investments.”

Shire has experienced tremendous sales growth, from $2.8 billion in 2008 to $4.8 billion in 2013, and is projected to climb to $10 billion by 2020.

Read more about the latest takeover bid in the Philadelphia Business Journal here as well on Philly.com here.