This week, the overall grades of four biotechnology stocks are lower, according to the Portfolio Grader database. 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. For more information, get Portfolio Grader’s complete analysis of TSRX stock.

Prosensa Holding NV (RNA) is having a tough week. The company’s rating falls from a C to a D. The stock gets F’s in Equity and Sales Growth. To get an in-depth look at RNA, get Portfolio Grader’s complete analysis of RNA stock.

Fibrocell Science, Inc. (FCSC) earns a D this week, falling from last week’s grade of C. The stock gets F’s in Equity, Cash Flow and Sales Growth. For more information, get Portfolio Grader’s complete analysis of FCSC stock.

Ambit Biosciences Corp.’s (AMBI) rating falls this week to an F (“strong sell”), down from last week’s D (“sell”). The stock gets F’s in Earnings Growth, Earnings Momentum and Equity. Cash Flow and Sales Growth also get F’s. To get an in-depth look at AMBI, get Portfolio Grader’s complete analysis of AMBI 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.