The ratings of seven Biotechnology stocks are down this week, according to the Portfolio Grader database. Each of these rates a “D” (“sell”) or “F” overall (“strong sell”).

Genomic Health (NASDAQ:GHDX) is on the decline this week, earning a D (“sell”) after receiving a C (“hold”) last week. Genomic Health is a life science company, which is focused on the development and commercialization of genomic-based clinical diagnostic tests for cancer that allow physicians and patients to make individualized treatment decisions. GHDX also rates an F in Portfolio Grader’s specific subcategory of Earnings Revisions. The stock’s trailing PE Ratio is 876.30. For a full analysis of GHDX stock, visit Portfolio Grader.

Acorda Therapeutics’ (NASDAQ:ACOR) rating weakens this week, dropping to a D versus last week’s C. Acorda Therapeutics is a commercial stage biopharmaceutical company dedicated to the identification, development and commercialization of novel therapies that improve neurological function in people with multiple sclerosis (MS), spinal cord injury and other disorders of the central nervous system. The stock gets F’s in Earnings Revisions and Sales Growth. For more information, get Portfolio Grader’s complete analysis of ACOR stock.

Amarin (NASDAQ:AMRN) earns a D this week, moving down from last week’s grade of C. Amarin focuses on developing the treatment for cardiovascular disease in the field of lipid science. The stock receives F’s in Earnings Growth, Earnings Revisions, Equity, and Cash Flow. As of Aug. 7, 2013, 15.6% of outstanding Amarin shares were held short. For a full analysis of AMRN stock, visit Portfolio Grader.

Exelixis (NASDAQ:EXEL) ratings are on the decline this week as the company earns an F (“strong sell”). Last week, it received a D (“sell”). Exelixisis a development-stage biotechnology company dedicated to the discovery and development of small-molecule therapeutics for the treatment of cancer and other serious diseases. The stock receives F’s in Earnings Growth, Earnings Momentum, and Equity. Margin Growth and Sales Growth also get F’s. As of Aug. 7, 2013, 19.2% of outstanding Exelixis shares were held short. To get an in-depth look at EXEL, get Portfolio Grader’s complete analysis of EXEL stock.

Slipping from a C to a D rating, Trius Therapeutics (NASDAQ:TSRX) takes a hit this week. Trius Therapeutics is a biopharmaceutical company. The stock gets F’s in Earnings Growth, Earnings Momentum, and Equity. Cash Flow and Sales Growth also get F’s. For more information, get Portfolio Grader’s complete analysis of TSRX stock.

This week, Discovery Laboratories’ (NASDAQ:DSCO) rating worsens to a D from the company’s C rating a week ago. Discovery Laboratories is a biotechnology company focused on developing products for the treatment of respiratory disease. The stock gets F’s in Equity and Cash Flow. To get an in-depth look at DSCO, get Portfolio Grader’s complete analysis of DSCO stock.

This week, Achillion (NASDAQ:ACHN) drops from a C to a D rating. Achillion focuses on the discovery, development and commercialization of innovative treatments for infectious diseases. The stock also gets an F in Equity. As of Aug. 7, 2013, 15.3% of outstanding Achillion shares were held short. For more information, get Portfolio Grader’s complete analysis of ACHN 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.