title: Didanosine resistance in HIV-infected patients switched from zidovudine to didanosine monotherapy.
abstract: OBJECTIVE
  To determine the frequency and pattern of development of specific drug resistance mutations for human immunodeficiency virus (HIV) reverse transcriptase in patients switched from zidovudine to didanosine therapy and to examine the relation of the didanosine resistance mutation at codon 74 of the HIV reverse-transcriptase gene to CD4+ T-cell changes and virus burden.
  
  
  METHODS
  Retrospective analysis of all patients enrolled at Stanford University in protocols where patients were switched from zidovudine to didanosine monotherapy.
  
  
  METHODS
  A university hospital.
  
  
  METHODS
  64 patients infected with HIV who were switched from zidovudine to didanosine monotherapy. Patients had the acquired immunodeficiency syndrome (AIDS), AIDS-related complex, or were asymptomatic (mean [+/- SD] starting CD4+ T-cell count of 129 +/- 88 cells/mm3).
  
  
  METHODS
  Serial serum specimens were tested for the didanosine resistance mutation at codon 74 of the HIV reverse-transcriptase gene and for a zidovudine resistance mutation at codon 215 using selective polymerase chain reactions (PCR). Serum HIV RNA levels were determined by quantitative PCR. CD4+ T-cell counts were determined at serial time points.
  
  
  RESULTS
  By 24 weeks of didanosine therapy, the proportion of patients with the didanosine resistance mutation at codon 74 increased from 0% to 56% (36 of 64). In contrast, the proportion of patients with the zidovudine resistance mutation at codon 215 decreased from 84% at the start to 59% after 24 weeks of didanosine therapy (a 25% decrease, 95% lower CI, 15%; P < 0.0001). Patients who developed the codon 74 mutation had a greater decrease in CD4+ T cells after the development of the mutation than did patients without the mutation (P < 0.001). In addition, after 24 weeks of didanosine, patients who developed the codon 74 mutation had a greater serum HIV RNA burden than patients who remained wild type (did not have the mutation) at codon 74 (225,000 compared with 82,400 HIV RNA copies/mL serum; P = 0.01).
  
  
  CONCLUSIONS
  Among patients infected with HIV who had advanced disease and were switched from zidovudine to didanosine therapy, more than one half developed the didanosine resistance mutation at codon 74 by 24 weeks of didanosine therapy. Patients who developed the codon 74 mutation had a greater decline in CD4+ T cells after the development of the mutation and had a greater serum virus burden than did patients without the codon 74 mutation.
authors.affiliation: Stanford University Medical Center, California 94305.
authors.forename: M J
authors.initials: MJ
authors.lastname: Kozal
authors.forename: K
authors.initials: K
authors.lastname: Kroodsma
authors.forename: M A
authors.initials: MA
authors.lastname: Winters
authors.forename: R W
authors.initials: RW
authors.lastname: Shafer
authors.forename: B
authors.initials: B
authors.lastname: Efron
authors.forename: D A
authors.initials: DA
authors.lastname: Katzenstein
authors.forename: T C
authors.initials: TC
authors.lastname: Merigan
mesh_terms: D015496:CD4-Positive T-Lymphocytes; D003062:Codon / Q000235:genetics; D016049:Didanosine / Q000627:therapeutic use*; D004352:Drug Resistance, Microbial / Q000235:genetics; D005814:Genes, Viral / Q000502:physiology; D006678:HIV / Q000201:enzymology / Q000235:genetics*; D015658:HIV Infections / Q000188:drug therapy* / Q000276:immunology; D006801:Humans; D007958:Leukocyte Count; D009154:Mutation; D012367:RNA, Viral / Q000235:genetics; D012194:RNA-Directed DNA Polymerase / Q000235:genetics*; D012189:Retrospective Studies; D015215:Zidovudine / Q000627:therapeutic use*
chemical_list: D003062:Codon; D012367:RNA, Viral; D015215:Zidovudine; D012194:RNA-Directed DNA Polymerase; D016049:Didanosine