LAVAL, Quebec— Valeant Pharmaceuticals International (NYSE: VRX and TSX: VRX)  said yesterday it will "improve" its $47 billion takeover offer for Allergan (NYSE: AGN), a day after Allergan’s board of directors rejected the hostile bid.

On Monday, Allergan’s board declared that Valeant’s proposal “substantially undervalues Allergan, creates significant risks and uncertainties for the stockholders of Allergan, and is not in the best interests of the Company and its stockholders.”

On April 22, Valeant announced its offer to acquire all of Allergan’s outstanding shares for a combination of 0.83 of Valeant common shares and $48.30 in cash per share of Allergan’s common stock. Valeant’s bid is backed by Allergan’s largest shareholder, Pershing Square, which holds a 9.7 percent stake in the company and is headed by activist investor William A. Ackman.

Valeant said it will announce its sweetened offer on a May 28 webcast.