IRVINE, Calif. (AP) — Botox maker Allergan spurned a takeover bid from Valeant Pharmaceuticals, saying that the unsolicited offer worth nearly $46 billion undervalues the company and carries significant risk.

Shortly after Canada's Valeant and activist investor Bill Ackman made their offer public last month, Allergan announced a so-called poison pill plan, a defensive tactic that makes a buyout prohibitively expensive. Allergan also told Valeant that it didn't want to discuss a tie-up, but said that it would evaluate the offer.

Valeant representatives did not immediately return calls from The Associated Press seeking comment early Monday.

Under the proposed deal, Valeant said that it would exchange each Allergan share for $48.30 in cash and a portion of shares of Valeant Pharmaceuticals International Inc.

Allergan stockholders would own 43 percent of the combined company under that proposal.

Ackman's Pershing Square Capital Management LP — Allergan's biggest stockholder at 9.7 percent — agreed to take only stock if the deal went through, and would remain as a long-term shareholder of the combined company.

Allergan said Monday that Valeant's uncertain long-term growth prospects and business model create a risk for Allergan shareholders.

"Valeant's strategy runs counter to Allergan's customer focused approach," Chairman and CEO David Pyott said in a letter to his counterpart at Valeant, Michael Pearson. "In particular, we question how Valeant would achieve the level of cost cuts it is proposing without harming the long term viability and growth trajectory of our business."

Allergan, based in Irvine, has long been considered one of the star performers in the specialty pharmaceutical sector. "Specialty pharmaceutical" is an industry term that differentiates smaller drugmakers from much bigger companies that sell a wide array of drugs, such as Pfizer and Merck.

Shares of Allergan Inc., which hit an all-time high this month, edged 12 cents higher before the opening bell Monday.