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Valeant Pharmaceuticals International Inc. and activist investor Bill Ackman’s Pershing Square Capital Management LP said Thursday they would team up in an attempt to force changes to the board of Irvine-based drug maker Allergan Inc.

Valeant, a Canadian drug maker with OC roots, has a hostile bid valued at about $46 billion for Allergan on the table. Pershing Square, which owns 10% of Allergan’s shares, is backing Valeant’s bid.

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Pershing Square and Valeant are planning to pursue a special meeting to change Allergan’s board.

Howard Schiller, Valeant’s chief financial officer, said in a release that it is ready to negotiate with Allergan. Valeant and Pershing are also planning to pursue a referendum of Allergan shareholders on whether they support having discussions with Valeant, Schiller said.

Allergan shares were down 1% to a market value of $48.9 billion in midday New York trading.