Clinical Use of Genotypic and Phenotypic Drug Resistance Testing to Monitor Antiretroviral Chemotherapy. Clin Infect Dis

Assays that detect antiretroviral drug resistance in human immunode®ciency virus have recently become available to clinicians. Phenotypic assays measure the drug susceptibility of the virus by determining the concentration of drug that inhibits viral replication in tissue culture. Genotypic assays determine the presence of mutations that are known to confer decreased drug susceptibility. Although each type of assay has speci®c advantages, limitations associated with these tests often complicate the interpretation of results. Several retrospective clinical trials have suggested that resistance testing may be useful in the assessment of the success of salvage antiretroviral therapy. Prospective, controlled trials have demonstrated that resistance testing improves short-term virological response. Resistance testing is currently recommended to help guide the choice of new drugs for patients after treatment has failed and for pregnant women. Resistance testing should also be considered for treatment-naõÈve patients, to detect transmission of resistant virus. Although the number of available antiretroviral agents has markedly increased in the past few years, the selection of a combination regimen that maximally suppresses HIV type 1 (HIV-1) replication continues to be challenging because of the potential of HIV-1 to develop drug resistance. For patients who have undergone antiretroviral therapy (hereafter referred to a