title: The impact of HIV drug resistance testing on changes to treatment.
abstract: BACKGROUND
  We investigate changes made to therapy after a resistance test result and identify factors associated with switching regimen.
  
  
  METHODS
  Patients receiving antiretroviral therapy (ART) who had a resistance test performed during 1998-2007 were included in the analysis. A switch was defined as starting at least two drugs/starting a drug from a class not previously experienced within 4 months of the resistance test result. Logistic regression was used to identify factors independently associated with switching regimen.
  
  
  RESULTS
  Of the 5123 test results included in the analyses, 1874 (36.6%) were followed by a switch within 4 months of the test result. Independent factors associated with switching included genotypic sensitivity score (GSS) of the current regimen [odds ratio (OR) 4.86, 95% confidence interval (CI) 3.95, 5.97 for GSS less than 1 compared to GSS of at least 3] and a higher number of previous failures [1.12 (1.06, 1.18) per additional failed regimen]. Patients with fewer drug options were less likely to switch [0.36 (0.27, 0.48) comparing 0-3 drug options with ≥10 drug options].
  
  
  CONCLUSIONS
  Only 37% of patients switched regimen within 4 months of the resistance test result. Whilst toxicity concerns of available drugs may somewhat explain this finding, it is also likely that there is a lack of treatment options available for patients who did not switch.
authors.affiliation: Research Department of Infection and Population Health, UCL Medical School, UK. l.bansi@ucl.ac.uk
authors.forename: Loveleen
authors.initials: L
authors.lastname: Bansi
authors.forename: Colette
authors.initials: C
authors.lastname: Smith
authors.forename: Andrew
authors.initials: A
authors.lastname: Phillips
authors.forename: Stuart
authors.initials: S
authors.lastname: Kirk
authors.forename: Anna-Maria
authors.initials: AM
authors.lastname: Geretti
authors.forename: Margaret
authors.initials: M
authors.lastname: Johnson
authors.forename: Nicola
authors.initials: N
authors.lastname: Mackie
authors.forename: Frank
authors.initials: F
authors.lastname: Post
authors.forename: Brian
authors.initials: B
authors.lastname: Gazzard
authors.forename: David
authors.initials: D
authors.lastname: Dunn
authors.forename: Caroline
authors.initials: C
authors.lastname: Sabin
mesh_terms: D000328:Adult; D044966:Anti-Retroviral Agents / Q000008:administration & dosage*; D003625:Data Collection; D004334:Drug Administration Schedule; D024882:Drug Resistance, Viral / Q000187:drug effects / Q000235:genetics; D005260:Female; D005838:Genotype; D015658:HIV Infections / Q000188:drug therapy / Q000235:genetics* / Q000821:virology; D015497:HIV-1 / Q000187:drug effects* / Q000235:genetics; D006801:Humans; D008297:Male; D008826:Microbial Sensitivity Tests; D019233:Retreatment; D016896:Treatment Outcome; D019562:Viral Load
chemical_list: D044966:Anti-Retroviral Agents