Benefits and limitations of testing for resistance to HIV drugs.

Since drug resistance was first described in HIV in 1989, great progress has been made in our understanding of its genetic basis and molecular mechanisms. Despite these advances and the introduction of many new antiretroviral drugs, resistance remains prevalent. The types of drug resistance tests and their relative advantages and disadvantages are reviewed. How and when these tests should be used to inform HIV clinical practice and their place in anti-HIV drug development are considered.