New data from a Phase III study of Fuzeon, an HIV fusion inhibitor marketed by Roche and Trimeris, presented at the International AIDS Society Conference on HIV Pathogenesis and Treatment in Paris show that the two-thirds of treatment-experienced patients who began a Fuzeon-based drug regimen achieved undetectable viral levels. Success in suppressing viral loads was dependent upon how far HIV disease had advanced in each study subject and how many other antiretroviral drugs they had taken. About 21% of patients who were resistant to all other existing anti-HIV medications were able to achieve an undetectable viral load when starting a Fuzeon-based drug cocktail. Among study subjects with T-cell counts over 100 who had previously taken between six and 10 anti-HIV medications, 68% were able to achieve an undetectable viral load after taking Fuzeon for 28 weeks. A separate study presented at the conference showed that almost all patients who achieved undetectable blood-based viral loads while taking Fuzeon maintained viral suppression through 48 weeks of treatment. The Food and Drug Administration approved Fuzeon on March 13. The injectable drug, the first ever to be developed in the fusion inhibitor class of anti-HIV medications, carries an annual price tag of about $20,000, making it the most expensive HIV antiretroviral drug on the market.