Carlsbad-based Isis Pharmaceuticals announced this morning that it has filed a patent infringement suit against Santaris Pharma, in the United States District Court of the Southern District of California. Isis said that Santaris is providing antisense drugs and drug discovery services, in violation of its patents. Isis said it has approximately 1,550 issued patents covering its antisense drugs. The company did not say what outcome it seeks in the patent infringement lawsuit.