title: Using different calculations of pharmacy refill adherence to predict virological failure among HIV-infected patients.
abstract: BACKGROUND
  Refill data are increasingly used to assess adherence in HIV-infected patients on combination antiretroviral therapy. However, it is not clear how feasible this method is when multiple pharmacies are involved. Also, the effects of inclusion of leftover medication from previous refills and prescribed treatment time on adherence calculations are unknown. We addressed these questions in the present study.
  
  
  METHODS
  Adult HIV-1-infected patients were recruited at the outpatient clinic of the Academic Medical Centre in Amsterdam and asked for their pharmacies' names. Refill data were obtained from pharmacies. Percentages of patients misclassified as nonadherent when disregarding leftover medication and prescribed treatment interruptions were calculated. Finally, we investigated whether an average adherence calculation of all drugs or a calculation based on one drug in the regimen best predicted virological failure (plasma HIV-1 RNA >40 copies/mL).
  
  
  RESULTS
  Two hundred one patients were included. Collecting data from multiple pharmacies (132) was found to be feasible. Forty-three percent of patients were misclassified as nonadherent when disregarding leftover medication and 2 percent when disregarding prescribed treatment time. There was no difference in predicting virological failure by different calculations of adherence.
  
  
  CONCLUSIONS
  These findings suggest that studies using pharmacy refill data should include leftover medication.
authors.affiliation: Department of Medical Psychology, Academic Medical Centre, Amsterdam, The Netherlands. marion.deboer@amc.uva.nl
authors.forename: I Marion
authors.initials: IM
authors.lastname: de Boer
authors.forename: Jan M
authors.initials: JM
authors.lastname: Prins
authors.forename: Mirjam A G
authors.initials: MA
authors.lastname: Sprangers
authors.forename: Pythia T
authors.initials: PT
authors.lastname: Nieuwkerk
mesh_terms: D000328:Adult; D019380:Anti-HIV Agents / Q000008:administration & dosage / Q000627:therapeutic use*; D015331:Cohort Studies; D011307:Drug Prescriptions; D004359:Drug Therapy, Combination; D005260:Female; D015658:HIV Infections / Q000188:drug therapy* / Q000821:virology*; D006801:Humans; D008297:Male; D055118:Medication Adherence; D008875:Middle Aged; D010349:Patient Compliance; D010604:Pharmacy
chemical_list: D019380:Anti-HIV Agents