As mega merger fever continues to grip the industry, Valeant and investor Bill Ackman, chief executive of Pershing Square Capital Management, have teamed up in bid to buy Botox maker Allergan in a deal worth around $46 billion.

The Canadian drugmaker has offered up $48.30 in cash and 0.83 shares of its stock in exchange for each Allergan share in the cash/stock deal.

But while group claims the move has come as a surprise, it sure moved quickly with a poison pill defence, announcing that its Board has 'unanimously' approved a new stockholder rights plan that essentially gives existing shareholders more power in the event that any single investor acquires more than 10%.

Allergan insists its move "is not intended to prevent an acquisition" on terms it considers favourable and in the best interests of all stockholders. "Rather, the plan aims to provide the board with adequate time to fully assess any proposal," it stressed. 

According to Valeant, a marriage with Allergan would create a company with an unrivalled portfolio in ophthalmology, dermatology, and cost savings of $2.7 billon annually, not to mention "significant revenue synergies".

"The combination of Valeant and Allergan represents the most strategic and value-creating transaction I have ever analysed," Ackman said, and he strongly urged Allergan's Board "to carefully examine the proposed transaction and enter into negotiations with Valeant so that a merger can be consummated promptly".