The development of resistance to established antiretroviral agents is a significant concern in patients with HIV infections. Resistance mutations may result from suboptimal exposure to anti-HIV drugs, and their occurrence increases with prolonged treatment; the development of antiretroviral agents that are effective against HIV strains resistant to established agents is therefore critical. Encouraging results from a recent phase II study suggest that the second-generation, nonpeptidic protease inhibitor (PI) tipranavir is effective in highly treatment-experienced patients with HIV infections, including those with resistance to multiple antiretroviral agents. Data presented at the 10th Conference on Retroviruses and Opportunistic Infections [Boston, US; February 2003] showed that 2 weeks' treatment with tipranavir plus ritonavir reduced HIV RNA levels from baseline. An analysis of viral resistance profiles showed that, despite having resistance to other PIs, nearly 70% of clinical isolates from patients enrolled in the study remained susceptible to tipranavir at baseline. Furthermore, tipranavir remained effective against HIV strains with 2-fold reductions in susceptibility to other PIs."This study shows tipranavir is active against HIV that has reduced sensitivity to commercially available protease inhibitors...tipranavir may[therefore]be a promising option for patients who have few or no treatment options because of drug resistance", said presenter Dr Joseph Gathe, from Baylor College of Medicine in Houston, US.