title: Evolution of resistance to drugs in HIV-1-infected patients failing antiretroviral therapy.
abstract: OBJECTIVE
  The optimal time for changing failing antiretroviral therapy (ART) is not known. It involves balancing the risk of exhausting future treatment options against the risk of developing increased drug resistance. The frequency with which new drug-resistance mutations (DRM) developed and their potential consequences in patients continuing unchanged treatment despite persistent viremia were assessed.
  
  
  METHODS
  A retrospective study of consecutive sequence samples from 106 patients at one institution with viral load (VL) of more than 400 copies/ml, with no change in ART for more than 2 months despite virologic failure.
  
  
  METHODS
  Two consecutive pol sequences, CD4 cell counts and VL were analyzed to quantify the development of new DRM and to identify changes in immunologic and virologic parameters. Genotypic susceptibility scores (GSS) and viral drug susceptibilities were calculated by a computer program (HIVDB). Poisson log-linear regression models were used to predict the expected number of mutations at the second time point.
  
  
  RESULTS
  : After a median of 14 months of continued ART, 75% (80 of 106) of patients acquired new DRM and were assigned a significantly lower GSS, potentially limiting the success of future ART. The development of new DRM was proportional to the time between the two sequences and inversely proportional to the number of DRM in the first sequence. However, the development of DRM was not associated with significant changes in CD4 or VL counts.
  
  
  CONCLUSIONS
  Despite stable levels of CD4 and VL over time, maintaining a failing therapeutic regimen increases drug resistance and may limit future treatment options.
authors.affiliation: Division of Infectious Diseases, Center for AIDS Research, Stanford University, Stanford, California, USA. rkantor@stanford.edu
authors.forename: Rami
authors.initials: R
authors.lastname: Kantor
authors.forename: Robert W
authors.initials: RW
authors.lastname: Shafer
authors.forename: Stephen
authors.initials: S
authors.lastname: Follansbee
authors.forename: Jonathan
authors.initials: J
authors.lastname: Taylor
authors.forename: David
authors.initials: D
authors.lastname: Shilane
authors.forename: Leo
authors.initials: L
authors.lastname: Hurley
authors.forename: Dong-Phuong
authors.initials: DP
authors.lastname: Nguyen
authors.forename: David
authors.initials: D
authors.lastname: Katzenstein
authors.forename: W Jeffrey
authors.initials: WJ
authors.lastname: Fessel
mesh_terms: D000328:Adult; D023241:Antiretroviral Therapy, Highly Active; D024882:Drug Resistance, Viral / Q000235:genetics*; D005260:Female; D015658:HIV Infections / Q000188:drug therapy* / Q000235:genetics; D015497:HIV-1; D006801:Humans; D008297:Male; D008875:Middle Aged; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D012044:Regression Analysis; D012189:Retrospective Studies; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D017211:Treatment Failure; D019562:Viral Load