Alexion Pharmaceuticals Inc., which has a drug manufacturing plant in Smithfield, has agreed to pay $25 million to PDL BioPharma Inc. to license patents used for Alexion’s Soliris anemia treatment, settling a lawsuit over claims that the company infringed the technology.

PDL, based in Fremont, Calif., sells licenses to biotechnology companies for medicines targeting cancers and viruses. Cheshire, Conn.-based Alexion used PDL’s antibodies without paying, PDL claimed.

As part of the accord, Alexion agreed that it won’t challenge the validity of the patents, the companies said in a joint statement.

Soliris, a treatment for chronic red-blood-cell destruction, reduces the need for transfusions. The medicine was approved in the United States and the European Union in 2007 as a treatment for patients with paroxysmal nocturnal hemoglobinuria, a life-threatening blood disease.

The use of Soliris, which is made at the company’s Rhode Island plant, as a treatment for other disorders is in early stages of investigation, the company said in the statement.

Alexion reported net sales of $71.2 million for Soliris shipped during its third quarter, ended Sept. 30, a 19-percent increase from the prior quarter.

The company was formed in 1992 and listed on Nasdaq in 1996. It employs approximately 500 people at its Connecticut headquarters, its Smithfield manufacturing plant, its European headquarters in Paris, its international operations center in Lausanne, Switzerland, and its local offices in major European countries.

PDL shares rose 5 cents to $6.30 in Nasdaq Stock Market trading. Alexion rose 87 cents to $37.