Canada's Valeant Pharmaceuticals is taking its hostile $50.8 billion bid to acquire Botox manufacturer Allergan directly to shareholders.

Backed by activist shareholder Bill Ackman's Pershing Square Capital Management, Allergan's biggest shareholder with 9.7%, announced on June 18 it had begun an exchange offer for the California company.

Allergan shareholders are being given the opportunity to trade each share for $72 in cash and 0.83 Valeant share, or all cash or all stock.

Allergan said its board would review the exchange offer. On June 10, it rejected the bid, which contained the same major terms.

Resolving the battle could be positive for Valeant, given the toll it has taken on the company's shares and its potential missed opportunities while focused on Allergan, one analyst told the news agency Reuters.

Another analyst suggested that Allergan may make an offensive move against the hostile bid by bidding for Ireland-based drugmaker Shire - a deal that could be more attractive than Valeant's proposal.

Such an acquisition would give Allergan shareholders sales diversification, sustainable organic growth and other benefits and spare them the risk of holding Valeant shares, the analyst said.

Valeant's offer will expire on Aug. 15, unless extended.