Amgen Inc. (NASDAQ: AMG) shares dropped over 2.42%  to $271.46 in pre trading session on Monday as the firm declared that It will pay $26.40 billion for Horizon Therapeutics Plc, a manufacturer of rare illness drugs, giving the biotech business access to a blockbuster thyroid eye disease medication.

The transaction will be Amgen’s largest to date, adding seven authorized products to the company’s portfolio, including Krystexxa, which is used to treat gout that is not managed by existing medications.

The acquisition might help Amgen combat increased competition for its top-selling arthritis medicine, Enbrel, from newly branded therapies, as well as the therapy’s patents expiring in 2029.

According to the article, the US biotechnology business has offered roughly $116.5 per Horizon share, citing a source familiar with the situation. The offer represents a 20% premium over Horizon’s Friday closing price of $97.29.

The news comes after French pharmaceutical company Sanofi announced on Sunday that it will no longer make an offer for Horizon.

Horizon Therapeutics, which has a market valuation of around $22 billion, announced last month that it was in negotiations with Amgen Inc, Sanofi, and Johnson & Johnson’s Janssen Global Services subsidiary, all of whom have been active in deal-making this year.

Amgen and Horizon did not react quickly to Reuters’ requests for comment. Janssen also withdrew from the competition last week, stating that it had no plans to make an offer for Horizon. Amgen is in advanced discussions to purchase Horizon, according to the Wall Street Journal.

Sanofi said in a statement that “transaction price estimates do not fulfill our value creation requirements.”

Janssen also dropped out of the contest last week, stating that it will not submit a bid for Horizon. Horizon, which develops medications for rare autoimmune and severe inflammatory disorders, anticipates Tepezza, which is used to treat thyroid eye disease, to generate more than $4 billion in worldwide annual peak sales.