Shares in Thousand Oaks-based biotech firm Amgen Inc. fell Monday after shares were downgraded by two firms.

One of the world’s largest biotechnology companies was cut to “market perform” from “outperform” by Sanford C. Bernstein & Co. analyst Geoffrey Porges

“Neither the company’s earnings multiple nor its earnings outlook are likely to improve through at least the first part of 2008,” analyst wrote in a research note.

Shares were also cut to “neutral” from “buy” by Merrill Lynch & Co. analyst Eric Ende.

This all comes as the drug company is facing decreasing sales of its popular anemia treatment Aranesp, after studies have found the drug increases certain health risks to users. Amgen sold $4.1 billion worth of anemia drugs last year.

Amgen dropped 2.4 percent to $50.83 in afternoon trading Monday on the Nasdaq. Shares have shed 29 percent so far this year.