Depomed Inc. said Monday that it would attempt to block Horizon Pharma PLC from using confidential data, a week after the company rejected Horizon's roughly $2 billion hostile takeover bid.

In a news release, Depomed said Horizon's bid is "predicated on the improper and unlawful use of highly confidential and proprietary information" relating to Depomed's leading pain drug. The company plans to file an injunction to prevent Horizon from continuing its alleged use of Depomed's data, and to prevent Horizon from making statements that Depomed claims are false.

The complaint, to be filed in the Superior Court of the State of California for the County of Santa Clara, follows the rejection by Depomed's board last week of Horizon's sweetened offer to buy the company at $33 a share.

The board has said the proposal is "not in the best interest" of the company, given that it is in a period of significant growth and is expected to benefit from its recent acquisition of the U.S. rights to painkiller Nucynta from Janssen Pharmaceuticals Inc., a unit of Johnson & Johnson.

Earlier Monday, Dublin-based Horizon submitted a written request to Depomed to schedule a special meeting allowing shareholders to vote on the proposed tie-up. Horizon also filed a lawsuit Monday to challenge the poison-pill measure Depomed recently adopted in an attempt to defend against the hostile bid. The rights plan would be triggered by a person or group acquiring a more than 10% stake in the company.

Horizon first made an all-stock offer to buy Depomed in a letter sent May 27, and then went public with the increased proposal mid-July after it was rejected by Depomed's board.

Shares in Depomed fell 1.3% in midday trading, while Horizon shares declined 3%.

Write to Lisa Beilfuss at lisa.beilfuss@wsj.com

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