By Jessica Toonkel
NEW YORK (Reuters) - Before Optimer Pharmaceuticals Inc even put itself up for sale earlier this year, Cubist Pharmaceuticals Inc offered to buy the antibiotic maker for $20 per share, or nearly $1 billion, two people familiar with the matter told Reuters on Wednesday.
The Cubist offer, which was made last summer and rejected, according to the people, would have represented a premium from the company's then share price of around $15 per share. The stock currently trades at more than $16 per share.
Optimer's stock closed Wednesday at $16.18, up almost 14 percent for the day on the news.
Cubist, which has a market value of just over $3 billion, is among a handful of participants in the sale, the people said. They asked not to be named because details of the auction are not public.
The company, as well as AstraZeneca Plc and Japan's Astellas Pharma Inc, made first-round bids for Optimer and are now working on final offers, one of the people said.
A date for second-round bids has not been set, but it is expected to be in early June, that person said.
A Cubist spokeswoman and an Optimer spokesman declined to comment. Calls to Astellas and AstraZeneca were not immediately returned.
In February, Optimer said it was exploring a sale and replaced its chief executive as part of a review of compliance issues, sending its shares up sharply.
Optimer, which makes a drug called Dificid used to treat intestinal infections, has existing partnerships with Astellas, AstraZeneca and Cubist.
Dificid, which treats adult patients who contract infectious diarrhea in hospitals, accounted for $62.4 million in sales in 2012. The company is expected to generate sales of $310 million from the drug by 2017, according Thomson Reuters data.
Optimer is also testing to see if the drug can prevent diarrhea in patients under 18 years and whether it can treat the condition in patients undergoing bone marrow transplants.
While Cubist may have made that offer last summer, Optimer is unlikely to attract a price that high now, said Brian Skorney, an analyst with Baird Equity Research.
Optimer announced flat sales growth of $16.8 million on Dificid for the first quarter of this year.
"I think it will get closer to $16 a share," Skorney added.
(Reporting By Jessica Toonkel, Editing by Soyoung Kim and Andre Grenon)