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

Trius Therapeutics, Inc. (TSRX) is on the decline this week, earning a D (“sell”) after receiving a C (“hold”) last week. 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.

This week, Rigel Pharmaceuticals, Inc. (RIGL) drops from a C to a D rating. Rigel Pharmaceuticals is a clinical-stage drug development company that discovers and develops novel, small-molecule drugs for the treatment of inflammatory and autoimmune diseases, as well as muscle disorders. The stock gets F’s in Equity and Cash Flow. For more information, get Portfolio Grader’s complete analysis of RIGL stock.

Aegerion Pharmaceuticals, Inc.’s (AEGR) rating falls this week to an F (“strong sell”), down from last week’s D (“sell”). Aegerion Pharmaceuticals is an emerging biopharmaceutical company focused on the development and commercialization of novel therapeutics to treat severe lipid disorders. The stock gets F’s in Earnings Revisions and Equity. As of Dec. 24, 2014, 25.4% of outstanding Aegerion Pharmaceuticals, Inc. shares were held short. To get an in-depth look at AEGR, get Portfolio Grader’s complete analysis of AEGR stock.

Arrowhead Research Corporation (ARWR) is having a tough week. The company’s rating falls from a C to a D. Arrowhead Research, a biopharmaceutical company, develops targeted RNAi therapeutics in the United States. The stock gets F’s in Earnings Revisions, Equity and Cash Flow. As of Dec. 24, 2014, 24.1% of outstanding Arrowhead Research Corporation shares were held short. For more information, get Portfolio Grader’s complete analysis of ARWR 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.