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

This week, Discovery Laboratories (NASDAQ:DSCO) falls to a D (“sell”), worse than last week’s grade of C (“hold”). Discovery Laboratories is a biotechnology company focused on developing products for the treatment of respiratory disease. In Portfolio Grader’s specific subcategories of Equity and Cash Flow, DSCO also gets F’s. The stock price has fallen 11.8% over the past month, worse than the Nasdaq, which has remained flat over the same period of time. For a full analysis of DSCO stock, visit Portfolio Grader.

Slipping from C to a D rating, Achillion (NASDAQ:ACHN) takes a hit this week. Achillion focuses on the discovery, development and commercialization of innovative treatments for infectious diseases. The stock also gets an F in Equity. Wall Street appears to agree with the stock downgrade, with share prices dropping 7.2% over the past month. As of March 20, 2013, 16.2% of outstanding Achillion shares were held short. For more information, get Portfolio Grader’s complete analysis of ACHN stock.

The rating of Genomic Health (NASDAQ:GHDX) declines this week from C to a D. 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. The stock also gets an F in Earnings Revisions. The stock has a trailing PE Ratio of 116.30. To get an in-depth look at GHDX, get Portfolio Grader’s complete analysis of GHDX stock.

This week, Acorda Therapeutics (NASDAQ:ACOR) drops from C to a D rating. 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 a full analysis of ACOR stock, visit Portfolio Grader.

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 March 20, 2013, 17.1% of outstanding Amarin shares were held short. To get an in-depth look at AMRN, get Portfolio Grader’s complete analysis of AMRN stock.

Exelixis’ (NASDAQ:EXEL) rating falls this week to an F (“strong sell”), down from last week’s 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 March 20, 2013, 20.6% of outstanding Exelixis shares were held short. For more information, get Portfolio Grader’s complete analysis of EXEL stock.

Trius Therapeutics (NASDAQ:TSRX) is having a tough week. The company’s rating falls from C to a D. 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 a full analysis of TSRX stock, visit Portfolio Grader.

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.