A physician's primer to antiretroviral drug resistance testing

Evaluating the genetic composition of HIV has evolved from a traditional epidemiologic research tool into a widely used clinical asset in the management of HIV infection. Genotypic and phenotypic testing is designed to identify drugs less likely to be therapeutically effective. Genotypic assays identify specific "gene mutations" or nucleotide substitutions known to confer drug resistance, whereas phenotypic assays measure the amount of drug necessary to inhibit viral replication in vitro. Prospective studies of antiretroviral drug resistance testing have shown its value as an independent predictor of optimal virologic response to drug therapy. Current guidelines recommend use of these tests following treatment failure and during pregnancy; considerations for testing include primary infection and treatment-naive patients. The identification of drug resistance can help the clinician individualize treatment regimens to attain maximal viral suppression and patient longevity.