The waiting period for Cubist Pharmaceuticals(CBST.DL) acquisition of Trius Therapeutics (NASDAQ: TSRX) under the Hart-Scott-Rodino Antitrust Improvements Act, or HSR, expired on Aug. 29, the company announced today, allowing the transaction to move to the next phase.

On Aug. 13, Cubist initiated a cash tender offer to buy Trius for $13.50 per share plus one contingent value right that entitles holders to receive an additional cash payment of up to $2.00 for each share they tender if certain commercial sales milestones are achieved. The tender offer expires at 9:00 a.m., Eastern Time, on Sept. 11.

The HSR requires merging companies to file detailed reports with the FTC and the Justice Department to see whether the combination violates antitrust laws. There's a 30-day waiting period (15 days for all-cash transactions) before the merger can be completed. The companies can request the waiting period be terminated early, which will be granted if both antitrust agencies complete their reviews and determine that no enforcement action is necessary.

The closing of the transaction is also conditioned on the tender of a majority of the outstanding shares of Trius' common stock and the satisfaction of other customary closing conditions.

Headquartered in Lexington, Mass., Cubist  is a biopharmaceutical company focused on the research, development, and commercialization of pharmaceutical products that address significant unmet medical needs in the acute care field.