An Amgen Inc. lawyer testified before a federal judge that the company's application for a patent covering its top-selling anemia drug Epogen was based on the "best information" available at the time. Michael Borun, under questioning by an attorney for rival drug maker Transkaryotic Therapies Inc., denied knowingly providing patent examiners with false information. Thousand Oaks-based Amgen, the world's largest biotechnology company, is suing to block Transkaryotic from selling its own version of Epogen, a drug used to stimulate red-blood cell production in kidney dialysis patients who become anemic. The drug is a form of the human protein erythropoietin. Transkaryotic contends Amgen's patents on Epogen should not be enforced because they were obtained through what's legally known as inequitable conduct, by intentionally withholding highly material information. This argument is among the key defenses that Transkaryotic has raised in response to Amgen's patent-infringement allegations. Cambridge, Mass.-based Transkaryotic is expected to present its final defense witnesses today in federal court in Boston, with closing arguments to follow. Drug makers, investors and patent attorneys have been monitoring the trial closely since it began in May--and not just because it involves a drug with estimated U.S. sales in 2000 of $4 billion.