title: Dropout in clinical trials of pharmacological treatment for methamphetamine dependence: the role of initial abstinence.
abstract: OBJECTIVE
  High rates of loss to follow-up represent a significant challenge to clinical trials of pharmacological treatments for methamphetamine (MA) use disorder. We aimed to estimate and test the relationship between achieving and maintaining abstinence in the initial weeks of study participation and subsequent retention in such trials, hypothesizing that participants able to achieve early abstinence would be less likely to drop out.
  
  
  METHODS
  Data from four randomized controlled trials (RCTs) of pharmacological treatments for MA use disorder were pooled and analyzed using a random-effects approach.
  
  
  METHODS
  All trials were conducted in the greater Los Angeles, CA, USA area.
  
  
  METHODS
  A total of 440 participants were included; trials were conducted between 2004 and 2014.
  
  
  METHODS
  Participants' ability to achieve a brief period of initial abstinence was measured as the number of MA-negative urine screens completed in the first 2 weeks of the trials. Outcomes were the likelihood of dropout, i.e. missing two consecutive weeks of scheduled urine drug screens, and the number of days participants were retained in the trials.
  
  
  RESULTS
  Study participants achieved an average of three (of six possible) negative urine screens during the first 2 weeks of the trials, 51% dropped out and the average number of days retained was 60 (of 90 maximum). Each additional negative urine screen achieved during the first 2 weeks of the study reduced multiplicatively the odds of dropout by 41% [odds ratio (OR) = 0.59, 95% confidence interval (CI) = 0.53, 0.66]. Abstinence was also a significant predictor of retention time; the hazard ratio for non-completion was 0.75 per additional negative urine screen (95% CI = 0.71, 0.80).
  
  
  CONCLUSIONS
  Participants in randomized controlled trials of pharmacological treatments for methamphetamine use disorder who are able to achieve a brief period of early abstinence are retained longer in the trials and are less likely to drop out overall.
authors.affiliation: Department of Epidemiology, Los Angeles Fielding School of Public Health, University of California, Los Angeles, CA, USA.|Departments of Family Medicine and Psychiatry and Biobehavioral Science, Los Angeles David Geffen School of Medicine, University of California, Los Angeles, CA, USA.
authors.forename: Ryan
authors.initials: R
authors.lastname: Cook
authors.affiliation: Departments of Family Medicine and Psychiatry and Biobehavioral Science, Los Angeles David Geffen School of Medicine, University of California, Los Angeles, CA, USA.|Centre for Population Health, Burnet Institute, Melbourne, VIC, Australia.
authors.forename: Brendan
authors.initials: B
authors.lastname: Quinn
authors.affiliation: Departments of Family Medicine and Psychiatry and Biobehavioral Science, Los Angeles David Geffen School of Medicine, University of California, Los Angeles, CA, USA.
authors.forename: Keith
authors.initials: K
authors.lastname: Heinzerling
authors.affiliation: Departments of Family Medicine and Psychiatry and Biobehavioral Science, Los Angeles David Geffen School of Medicine, University of California, Los Angeles, CA, USA.
authors.forename: Steve
authors.initials: S
authors.lastname: Shoptaw
mesh_terms: D000328:Adult; D019969:Amphetamine-Related Disorders / Q000188:drug therapy*; D005260:Female; D006801:Humans; D015141:Los Angeles; D059012:Lost to Follow-Up; D008297:Male; D008694:Methamphetamine; D010352:Patient Dropouts / Q000706:statistics & numerical data*; D016032:Randomized Controlled Trials as Topic
chemical_list: D008694:Methamphetamine
keywords: Abstinence; clinical trials; dropout; methamphetamine; pharmacotherapy; retention