The overall ratings of three biotechnology stocks are down on Portfolio Grader this week. Each of these rates a “D” (“sell”) or “F” overall (“strong sell”).

Trius Therapeutics, Inc.’s (TSRX) rating falls to a D (“sell”) this week, down from C (“hold”) the week prior. Trius Therapeutics is a biopharmaceutical company. In Portfolio Grader’s specific subcategories of Earnings Growth, Earnings Momentum, Equity, Cash Flow and Sales Growth, TSRX also gets F’s. To get an in-depth look at TSRX, get Portfolio Grader’s complete analysis of TSRX stock.

Ambit Biosciences Corp. (AMBI) ratings are on the decline this week as the company earns an F (“strong sell”). Last week, it received a D (“sell”). The stock receives F’s in Earnings Momentum, Earnings Revisions and Equity. Cash Flow and Sales Growth also get F’s. Shares of the stock have been exchanging at an usually rapid pace, twice the rate of the week prior. For more information, get Portfolio Grader’s complete analysis of AMBI stock.

Portola Pharmaceuticals, Inc. (PTLA) experiences a ratings drop this week, going from last week’s C to a D. In Equity, Cash Flow, Margin Growth and Sales Growth the stock gets F’s. To get an in-depth look at PTLA, get Portfolio Grader’s complete analysis of PTLA stock.

Louis Navellier’s proprietary Portfolio Grader stock ranking system assesses roughly 5,000 companies every week based on a number of fundamental and quantitative measures. Stocks are given a letter grade based on their results — with A being “strong buy,” and F being “strong sell.” Explore the tool here.