title: Loss of antiretroviral drug susceptibility at low viral load during early virological failure in treatment-experienced patients.
abstract: BACKGROUND
  Clinical studies have demonstrated a correlation between the response to second-line antiretroviral therapy and the number of drugs in the regimen to which the virus is susceptible. These studies have largely been performed in patients with viral loads over 1000 copies/ml.
  
  
  OBJECTIVE
  To examine the evolution of resistance during early virological failure, and the potential role of susceptibility testing in patients with low viral loads (below 1000 copies/ml), in treatment-experienced patients.
  
  
  METHODS
  Drug susceptibility and genotypes of HIV-1 from indinavir-experienced patients undergoing therapy with nelfinavir, saquinavir, abacavir and either a second nucleoside reverse transcriptase inhibitor (NRTI) or nevirapine were determined.
  
  
  RESULTS
  Sixteen subjects were studied. Five of the ten subjects treated with nevirapine, and one of six treated with a second NRTI, achieved and maintained plasma HIV RNA < 500 copies/ml. Virus from the treatment failures lost susceptibility to one or more treatment drugs, including nelfinavir and/or saquinavir, after 4 to 36 weeks of treatment. In six of the ten failures, virus with new reductions in drug susceptibility was detected prior to failure. In five of the six failures who had at least one plasma sample with a viral load between 50 and 1000 copies/ml, reductions in susceptibility to one or more treatment drugs were detected (viral load range: 260 to 630 copies/ml).
  
  
  CONCLUSIONS
  Drug resistance can be detected at viral loads below 1000 copies/ml which may be predictive of treatment failure. Failure of a second line regimen was typically associated with early evolution of resistance in HIV protease.
authors.affiliation: ViroLogic Inc., South San Francisco, California 94080, USA. nparkin@virologic.com
authors.forename: N T
authors.initials: NT
authors.lastname: Parkin
authors.forename: S G
authors.initials: SG
authors.lastname: Deeks
authors.forename: M T
authors.initials: MT
authors.lastname: Wrin
authors.forename: J
authors.initials: J
authors.lastname: Yap
authors.forename: R M
authors.initials: RM
authors.lastname: Grant
authors.forename: K H
authors.initials: KH
authors.lastname: Lee
authors.forename: D
authors.initials: D
authors.lastname: Heeren
authors.forename: N S
authors.initials: NS
authors.lastname: Hellmanna
authors.forename: C J
authors.initials: CJ
authors.lastname: Petropoulos
mesh_terms: D019380:Anti-HIV Agents / Q000494:pharmacology* / Q000627:therapeutic use*; D004352:Drug Resistance, Microbial / Q000235:genetics; D004359:Drug Therapy, Combination; D015658:HIV Infections / Q000188:drug therapy*; D016333:HIV Protease / Q000235:genetics; D054303:HIV Reverse Transcriptase / Q000235:genetics; D015497:HIV-1 / Q000187:drug effects* / Q000235:genetics / Q000502:physiology*; D006801:Humans; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D018894:Reverse Transcriptase Inhibitors / Q000494:pharmacology / Q000627:therapeutic use; D016879:Salvage Therapy; D017211:Treatment Failure; D019562:Viral Load
chemical_list: D019380:Anti-HIV Agents; D018894:Reverse Transcriptase Inhibitors; D054303:HIV Reverse Transcriptase; D016333:HIV Protease