Understanding HIV Phenotypic Resistance Testing: Usefulness in Managing Treatment-Experienced Patients

This review discusses how “virtualâ€? and conventional phenotypic assays establish clinical cutoffs predictiveof response in HIV isolates from antiretroviral-experienced patients. Sophisticated phenotypicassays that incorporate linear regression modeling and conventional phenotypic assays have beenused to define and validate clinical cutoffs (i.e. the correlation between viral susceptibility and treatmentresponse) for most antiretrovirals, including the newer protease inhibitors. Using these clinicalcutoff values, clinical data show that the newer protease inhibitors retain activity against the majorityof isolates from treatment-experienced patients and from those with baseline resistance to multipleprotease inhibitors. The utility of phenotypic resistance testing methods have therefore been validatedin the clinical setting. In summary, HIV drug resistance testing is currently the recommended standardof care for the selection of antiretroviral regimens for HIV-infected patients in multiple clinical settings.An understanding of the basic principles of phenotypic resistance testing is crucial for providingoptimal care, particularly for antiretroviral-experienced patients.