title: Phenotypic and genotypic resistance to nucleoside reverse transcriptase inhibitors in HIV-1 clinical isolates.
abstract: OBJECTIVE
  To assess phenotypic and genotypic cross-resistance to nucleoside reverse transcriptase inhibitors in patients treated with a combination including zidovudine, who were switched to a combination including stavudine.
  
  
  METHODS
  We analysed 24 clinical HIV-1 isolates from 12 patients before and several months after therapeutic switching. Plasma HIV-1 RNA was measured using quantitative polymerase chain reaction (Roche). Genotypic resistance was measured by sequencing the reverse transcriptase gene from plasma HIV-1 RNA. Phenotypic resistance was measured using a recombinant assay (Virco).
  
  
  RESULTS
  Patients were treated with a combination including zidovudine for a mean (+/- SEM) period of 21.8 +/- 3.5 months and had a plasma viral load of 4.1 +/- 0.2 log HIV-1 RNA copies/mL (time 1). After a mean period of 19.3 +/- 1.6 months following the therapeutic change, the plasma viral load was 3.6 +/- 0.1 log copies/mL (time 2). At time 1, genotypic resistance to zidovudine was found in all cases (41L: four cases; 41L, 215Y: five cases; 41L, 210W, 215Y: two cases; K70R: one case) with a mean 6.6 +/- 1.6-fold increase in the median inhibitory concentration (IC50) to zidovudine and 1.7 +/- 0.4-fold to stavudine. At time 2, genotypic resistance to zidovudine was found in 11 out of 12 cases (41L: two cases; 41L, 215Y: six cases; 41L, 210W, 215Y: two cases; M41L, D67N, L210W, T215Y: one case) with a mean 18.9 +/- 8.8-fold increase in the IC50 to zidovudine and 1.4 +/- 0.4-fold to stavudine
  
  
  CONCLUSIONS
  In this clinical series of patients with suboptimal control of plasma HIV-1 RNA using a combination including zidovudine, the presence of zidovudine-related mutations was associated with a decreased phenotypic sensitivity to this drug. Despite persistent HIV-1 replication, switching to stavudine was associated with a further decrease in phenotypic sensitivity to zidovudine but not to stavudine after 19 months. These data suggest that stavudine remains a possible option in zidovudine-experienced patients.
authors.affiliation: Department of Infectious Diseases and Laboratory of Virology, General Hospital, Toulon, France. avps@club-internet.fr
authors.forename: A
authors.initials: A
authors.lastname: Lafeuillade
authors.forename: C
authors.initials: C
authors.lastname: Poggi
authors.forename: G
authors.initials: G
authors.lastname: Hittinger
authors.forename: S
authors.initials: S
authors.lastname: Chadapaud
mesh_terms: D000328:Adult; D019380:Anti-HIV Agents / Q000494:pharmacology / Q000627:therapeutic use*; D023241:Antiretroviral Therapy, Highly Active / Q000009:adverse effects / Q000379:methods; D004279:DNA, Viral / Q000187:drug effects* / Q000235:genetics*; D024882:Drug Resistance, Viral; D005260:Female; D005838:Genotype; D015658:HIV Infections / Q000097:blood / Q000188:drug therapy* / Q000821:virology*; D015497:HIV-1 / Q000235:genetics*; D006801:Humans; D008297:Male; D008826:Microbial Sensitivity Tests; D009154:Mutation / Q000235:genetics; D018579:Patient Selection; D010641:Phenotype; D016133:Polymerase Chain Reaction; D012367:RNA, Viral / Q000097:blood* / Q000187:drug effects / Q000235:genetics; D018894:Reverse Transcriptase Inhibitors / Q000494:pharmacology / Q000627:therapeutic use*; D018119:Stavudine / Q000494:pharmacology / Q000627:therapeutic use*; D013997:Time Factors; D017211:Treatment Failure; D019562:Viral Load; D015215:Zidovudine / Q000494:pharmacology / Q000627:therapeutic use*
chemical_list: D019380:Anti-HIV Agents; D004279:DNA, Viral; D012367:RNA, Viral; D018894:Reverse Transcriptase Inhibitors; D015215:Zidovudine; D018119:Stavudine