"This study is a significant step forward in understanding how HIV reacts to drugs at varying degrees of susceptibility and how that affects a patient's clinical response," said Dr. Nancy Shulman, fellowship program director in the infectious disease division at the Stanford University School of Medicine and lead author of the study. "Arming physicians with reliable information on HIV resistance and susceptibility, including hypersusceptibility, can help them treat patients more effectively."

In the study, researchers retrospectively examined blood samples taken from 30 treatment-experienced patients. Each sample's drug susceptibility profile was measured using PhenoSense HIV, and resistance-related mutations were identified using a genotypic test. Researchers compared these data with viral load test results to determine the impact of hypersusceptibility on patient outcomes.

They found that patients with virus that was hypersusceptible to non- nucleoside reverse transcriptase inhibitors (NNRTIs), a class of HIV drugs, and who had no resistance mutations to these drugs, experienced significantly greater responses to NNRTI-based therapy over the 24-week study period than those patients without hypersusceptibility. Patients with hypersusceptible virus experienced a 20-fold greater reduction in viral load over those without hypersusceptible virus.

"We have identified a new, clinically relevant marker for HIV patient management," said Dr. Nicholas Hellmann, study co-author and ViroLogic's Vice President of Clinical Research. "After years spent studying HIV drug resistance, we are beginning to understand the flip-side-hypersusceptibility. The additional information provided by PhenoSense HIV may help physicians design even more effective individualized treatment regimens for their patients."

In addition to providing insight on hypersusceptibility, the research team also described the unique phenomenon of HIV "re-sensitization," in which virus that was resistant to treatment with NNRTIs actually appeared to become susceptible again. Detection and measurement of re-sensitization may have important implications for the long-term management of HIV infection, since it may expand a patient's treatment options, an important consideration for the 200,000 patients who face treatment failure due to drug resistance every year.

PhenoSense HIV is a rapid, highly sensitive drug resistance assay that allows physicians to directly and reliably measure clinically significant levels of HIV drug resistance and susceptibility. With this information, physicians can individualize treatment regimens for their patients to maintain effective therapy and avoid unnecessary side effects, resulting in improved outcomes and reduced treatment costs. Pharmaceutical companies are also using ViroLogic's assay to develop new drugs to which HIV might be less resistant.

About ViroLogic

ViroLogic is a biotechnology company advancing the fields of individualized medicine and pharmacogenomics, helping to make them realities in healthcare around the world today. The Company discovers, develops and markets innovative products to guide and improve treatment of serious viral diseases such as AIDS and hepatitis. Its leading expertise in virology, molecular biology, clinical research, engineering, information systems, and quality assurance has resulted in technology to assess drug resistance and susceptibility in viruses that cause these diseases, which affect millions of people worldwide.

The Company's current products are designed to optimize HIV/AIDS treatment regimens, providing physicians with important information to help select appropriate drugs for their patients and leading to better outcomes and reduced costs. These products are also being used by major pharmaceutical companies working to develop new and improved antiviral therapeutics that can be more effective in an increasingly drug-resistant environment.

Certain statements in this press release are forward-looking, including statements relating to the performance of the Company's testing products. These forward-looking statements are subject to risks and uncertainties and other factors, which may cause actual results to differ materially from the anticipated results or other expectations expressed in such forward-looking statements. These risks and uncertainties include, but are not limited to, whether PhenoSense(TM) HIV will achieve market acceptance, whether payers will authorize reimbursement for our products, whether we will be able to expand our sales and marketing capabilities, whether we encounter problems or delays in automating our process, whether we successfully introduce new products using our PhenoSense(TM) technology, whether intellectual property underlying our PhenoSense(TM) technology is adequate, whether we are able to build brand loyalty, and other risks and uncertainties detailed from time to time in our reports to the Securities and Exchange Commission, including our Annual Report on Form 10-K for the year ended December 31, 2000.

SOURCE ViroLogic Inc.

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