title: Virologic efficacy of boosted double versus boosted single protease inhibitor therapy.
abstract: OBJECTIVE
  Although regimens containing two protease inhibitor (PI) together with ritonavir boosting are used with the aim of improving virologic response to salvage therapy, there is little evidence to support or reject this approach. We compared the probability of attaining an undetectable HIV RNA level after using either boosted double or boosted single PI regimens.
  
  
  METHODS
  Retrospective clinical cohort.
  
  
  METHODS
  PI-experienced subjects in a Northern California-based database who initiated either a boosted single or boosted double PI salvage therapy regimen were analysed. Traditional multivariable regression and marginal structural model analyses were used to compare the effects of the two regimens on virologic suppression 12-36 weeks after initiation of salvage therapy, controlling for confounding by baseline HIV RNA level, CD4 lymphocyte count, treatment history, drug resistance, and multiple characteristics of the salvage regimen.
  
  
  RESULTS
  Fifty-one percent of boosted single PI regimens (n=805) and 51.6% of boosted double PI regimens (n=183) achieved a plasma HIV RNA level of <75 copies/ml at week 12-36. In models including multiple potentially confounding variables, estimates of the relative odds of suppression on boosted double versus boosted single PI regimens ranged from 1.17 (95% CI, 0.54-2.55) to 1.33 (95% CI, 0.82-2.14).
  
  
  CONCLUSIONS
  We were not able to reject the null hypothesis that boosted double versus boosted single PI regimens, resulted in equivalent probabilities of virologic success.
authors.affiliation: Division of Biostatistics, School of Public Health, University of California, Berkeley, CA 94720, USA. mayaliv@berkeley.edu
authors.forename: Maya L
authors.initials: ML
authors.lastname: Petersen
authors.forename: Yue
authors.initials: Y
authors.lastname: Wang
authors.forename: Mark J
authors.initials: MJ
authors.lastname: van der Laan
authors.forename: Soo-Yon
authors.initials: SY
authors.lastname: Rhee
authors.forename: Robert W
authors.initials: RW
authors.lastname: Shafer
authors.forename: W Jeffrey
authors.initials: WJ
authors.lastname: Fessel
mesh_terms: D023241:Antiretroviral Therapy, Highly Active / Q000379:methods; D018791:CD4 Lymphocyte Count; D004341:Drug Evaluation; D024882:Drug Resistance, Viral; D015658:HIV Infections / Q000188:drug therapy* / Q000276:immunology / Q000821:virology; D017320:HIV Protease Inhibitors / Q000627:therapeutic use*; D015497:HIV-1 / Q000235:genetics / Q000302:isolation & purification*; D006801:Humans; D012367:RNA, Viral / Q000097:blood; D012189:Retrospective Studies; D016879:Salvage Therapy / Q000379:methods*; D016896:Treatment Outcome; D019562:Viral Load
chemical_list: D017320:HIV Protease Inhibitors; D012367:RNA, Viral