title: Comparison of abacavir/lamivudine and tenofovir/emtricitabine among treatment-naive HIV-infected patients initiating therapy.
abstract: BACKGROUND
  Controversy about the relative performance of abacavir (ABC)/lamivudine (3TC) and tenofovir (TDF)/emtricitabine (FTC) in initial combination antiretroviral therapy (cART) exists.
  
  
  METHODS
  We compared the times to regimen failure (composite of virologic failure or switching/stopping nucleosides for any reason) according to nucleoside backbone in treatment-naive patients starting cART in a retrospective observational cohort study. Additional endpoints included virologic failure, switching/stopping nucleosides for nonvirologic reasons, and virologic suppression. Treatment-naive noninjection drug user individuals in the Canadian Observational Cohort initiating ABC/3TC-containing or TDF/FTC-containing cART with efavirenz, nevirapine, lopinavir/ritonavir, or atazanavir/ritonavir with ≥6 months follow-up were included. Multivariable proportional hazards regression models accounting for competing risks were used to model outcomes.
  
  
  RESULTS
  One thousand seven hundred sixty-four individuals (588 ABC/3TC, 1176 TDF/FTC) were included. Median (interquartile range) follow-up times were 34 (23-50) and 20 (13-30) months, respectively. Time to regimen failure was similar for ABC/3TC versus TDF/FTC [adjusted hazard ratio, (aHR) = 0.96, 95% CI = 0.80 to 1.17] after adjusting for baseline viral load (VL), sex, province, third antiretroviral agent, year of cART initiation, HLA-B*5701 test availability, and rate of VL testing. No differences were observed in time to virologic failure (aHR = 0.84, 95% CI = 0.58 to 1.20), switching/stopping nucleosides for nonvirologic reasons (aHR = 1.02, 95% CI = 0.81 to 1.28), or virologic suppression (aHR = 0.96, 95% CI = 0.83 to 1.10). There was no statistical interaction between backbone and baseline VL for any outcome. Results were similar when stratified by baseline VL ≤ 100,000 or > 100,000 copies per milliliter.
  
  
  CONCLUSIONS
  In our naive noninjection drug user HIV-infected patients starting cART, there was no difference in time to regimen failure, virologic failure, switching/stopping nucleosides, or virologic suppression with ABC/3TC versus TDF/FTC.
authors.affiliation: Department of Medicine, University of Toronto, Ontario, Canada.
authors.forename: Darrell H S
authors.initials: DH
authors.lastname: Tan
authors.forename: Keith
authors.initials: K
authors.lastname: Chan
authors.forename: Janet
authors.initials: J
authors.lastname: Raboud
authors.forename: Curtis
authors.initials: C
authors.lastname: Cooper
authors.forename: Julio S G
authors.initials: JS
authors.lastname: Montaner
authors.forename: Sharon
authors.initials: S
authors.lastname: Walmsley
authors.forename: Robert S
authors.initials: RS
authors.lastname: Hogg
authors.forename: Marina B
authors.initials: MB
authors.lastname: Klein
authors.forename: Nima
authors.initials: N
authors.lastname: Machouf
authors.forename: Sean B
authors.initials: SB
authors.lastname: Rourke
authors.forename: Chris
authors.initials: C
authors.lastname: Tsoukas
authors.forename: Mona R
authors.initials: MR
authors.lastname: Loutfy
mesh_terms: D000225:Adenine / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000627:therapeutic use; D000328:Adult; D019380:Anti-HIV Agents / Q000008:administration & dosage / Q000627:therapeutic use*; D002170:Canada; D015331:Cohort Studies; D003841:Deoxycytidine / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000627:therapeutic use; D015224:Dideoxynucleosides / Q000627:therapeutic use*; D004338:Drug Combinations; D057915:Drug Substitution; D000068679:Emtricitabine; D005260:Female; D015658:HIV Infections / Q000188:drug therapy*; D006801:Humans; D019259:Lamivudine / Q000627:therapeutic use*; D008297:Male; D008875:Middle Aged; D063065:Organophosphonates / Q000008:administration & dosage / Q000627:therapeutic use*; D012189:Retrospective Studies; D000068698:Tenofovir; D017211:Treatment Failure; D014779:Virus Replication / Q000187:drug effects; D000099227:Abacavir
chemical_list: D000225:Adenine; D019380:Anti-HIV Agents; D003841:Deoxycytidine; D015224:Dideoxynucleosides; D004338:Drug Combinations; D000068679:Emtricitabine; D019259:Lamivudine; D063065:Organophosphonates; D000068698:Tenofovir; C492871:abacavir, lamivudine drug combination; D000099227:Abacavir