Irvine-based Allergan Inc. said today that it filed an answer in U.S. District Court to a countersuit filed by Valeant Pharmaceuticals International Inc. and activist investor Bill Ackman’s Pershing Square Capital Management.

Allergan is fighting a hostile takeover bid by Canada-based Valeant that is supported by Ackman, who holds just under 10% of the Botox maker.

Allergan said in a release that the answer addressed its statements “on the unsustainability of Valeant’s underlying business model.”

Valeant and Pershing filed its counterclaim against Allergan in late August, roughly three weeks after Allergan sued the duo in an effort to halt the takeover bid.

Allergan’s earlier lawsuit contended Valeant Pharmaceuticals International Inc. and activist investor Bill Ackman engaged in insider trading when Pershing Square bought $3.2 billion of Allergan shares, while knowing Valeant’s takeover intentions. The drug maker said this deprived selling shareholders of $1.2 billion in value gains.

Shares of Allergan were flat this morning with a market value of $48.8 billion. Valeant shares were up 1% to $39.7 billion.