US drugmaker Allergan, which makes the Botox anti-wrinkle treatment, said it has reached agreement with suitors Pershing Square Capital Management and Canada's Valeant Pharmaceuticals to hold a special shareholder meeting on the originally scheduled date of Dec. 18.

The two latter companies, closely tied to investment activist shareholder Bill Ackman, also have agreed to dismiss their pending litigation before the Delaware Court of Chancery, Allergan added.

Together Pershing Square, Allergan's largest shareholder with a 9.72% stake and Valeant made a $52 billion hostile offer for Allergan in April. In August, they sued the target company, alleging it was trying to avoid a special meeting to give it time to find an alternative deal. Allergan subsequently called the meeting for the December date.

Since the initial takeover approach, Allergan has been fighting for investor support for its own standalone plan that includes cost cuts and making an acquisition of its own.

To force the company to the table, Ackman has been pushing for a special meeting where he hopes to replace most board members with his own nominees, who he expects will be more receptive to Valeant's bid.