Amgen’s stock fell $2 Thursday, a day...

Amgen’s stock fell $2 Thursday, a day after a Massachusetts court ruled that it was violating the patent of a rival biotechnology company, Genetics Institute of Cambridge, Mass. The Thousand Oaks company’s stock closed at $33.75. Both companies claim to have exclusive patents to manufacture erythropoietin, an anti-anemia drug that, analysts say, once approved by federal officials will be worth at least $300 million annually to its manufacturer. An Amgen spokesman said it still expects to eventually win in court exclusive rights to the drug.