Cubist Pharmaceuticals will acquire Optimer Pharmaceuticals and Trius Therapeutics, valuing each company at more than $800 million. Both companies are developing drugs to combat bacterial infections often associated with hospital stays.

Optimer’s Dificid won regulatory approval in May 2011 to treat C-difficile associated diarrhea, while Trius’ late-stage antibiotic for the treatment of gram-positive infections, including MRSA, complements Cubist’s pipeline. Both deals involve an upfront cash payment and contingent value rights based on the achievement of sales milestones.

Cubist CEO Michael Bonney says both acquisitions are a natural fit for his company, which has positioned itself to focus on acute care environments. Cubist already co-promotes Optimer’s Dificid in the United States.

Cubist’s deal for Optimer is valued at $801 million. It will pay $10.75 per share in cash for Optimer, valuing the company at $535 million on a fully diluted basis. Each Optimer shareholder will also receive a publicly tradable contingent value right that entitles the holder to receive an additional one-time cash payment of up to $5.00 for each share they own if certain net sales of Dificid are achieved.

Cubist’s deal to acquire Trius is valued at up to $818 million. Cubist will pay approximately $707 million upfront for the biotech, or $13.50 per share. Each Trius stockholder will also receive one non-tradable contingent value right, entitling the holder to receive an additional cash payment of up to $2.00 for each share they own if certain commercial sales milestones are achieved. Trius expects to submit a new drug application for its antibiotic, tedizolid phosphate, to U.S. regulatory authorities in the second half of 2013 and seek approval in the European Union in the first half of 2014.

The boards of directors of Cubist, Optimer, and Trius have approved the transactions and both deals are expected to close by the end of the year.