The activist investor William A. Ackman plans to team up with Valeant Pharmaceuticals to make a bid for the maker of Botox cosmetic treatments, Allergan, the hedge fund manager disclosed in a regulatory filing on Monday.
A bid would be one of the biggest takeover offers announced so far this year. Allergan had a market value of about $42 billion as of Monday afternoon.
The union of Mr. Ackman and Valeant is an unusual pairing of activist hedge fund and hostile bidder, putting together one of the most prominent hedge fund managers with a drug maker known for its serial acquisitions.
Mr. Ackman said in the regulatory filing that he had acquired a stake of nearly 10 percent in Allergan and supports a merger of the two pharmaceutical companies. Should a deal be completed, his firm, Pershing Square Capital Management, would retain a big stake in the combined drug maker.
It isn’t clear how much Valeant, whose deals have included the $8.7 billion takeover of the eye care products maker Bausch & Lomb and the $2.6 billion purchase of Medicis, will pay.
In the regulatory filing, Pershing Square said that it expected the cash component of an offer to total $15 billion, with financing to be provided by Barclays and the Royal Bank of Canada.
Shares in Allergan were up more than 16 percent in after-hours trading after The Wall Street Journal reported the plans of Mr. Ackman and Valeant.
Valeant said in a statement: “We firmly believe that combining Valeant and Allergan would create an unrivaled platform for growth and value creation in healthcare, and we look forward to finalizing and announcing the terms of our proposal shortly.â€
Mr. Ackman and representatives for Allergan declined to comment.
David Gelles contributed reporting.
