San Diego-based biopharmaceutical company Optimer Pharmaceuticals Inc. stands to gain $90 million or more through an exclusive license it granted to Tokyo-based Astellas Pharma Inc. for the anti-infective drug fidaxomicin.

Astellas Pharma has agreed to pay $20 million upfront, plus as much as $70 million more, to develop and commercialize Optimer’s drug in Japan.

Fidaxomicin treats Clostridium difficile-associated diarrhea, which has become a significant medical problem in hospitals and long-term-care facilities. The illness causes inflammation of the colon, severe diarrhea and, in the most serious cases, death.

Under terms of the deal, Astellas is responsible for all future costs associated with the development and commercialization of fidaxomicin in Japan.

"We believe that fidaxomicin's highly differentiated clinical profile, which has been confirmed by clinical studies conducted in the U.S. and EU, has the potential to provide a new and unique treatment option for patients in Japan,” Yoshihiko Hatanaka, president and CEO of Astellas Pharma, said in a statement.

Optimer President and CEO Pedro Lichtinger said Japan is a key territory that the company has targeted for geographic market expansion.

In 2011, Optimer entered into a commercial partnership with Astellas Pharma Europe Ltd. to develop and market fidaxomicin under the trade name Dificlir in Europe and certain other countries in the Middle East, Africa and the Commonwealth of Independent States.

Fidaxomicin is sold in the United States under the trade name Dificid.