Incidence and factors associated with discontinuation of opioid agonist therapy among people who inject drugs in Australia.

Abstract

To estimate incidence and predictors of opioid agonist therapy (OAT) discontinuation in a national cohort of people who inject drugs (PWID). Annually repeated cross-sectional serosurveillance among PWID attending ~50 needle-syringe programmes across Australia. Between 1995 and 2018, 2651 PWID who reported current OAT and had subsequent survey participation completed 6739 surveys. Respondents were followed over 11 984 person-years of observation (PYO). Respondents were predominantly male (60%), and the median age was 34years. Heroin was the most commonly reported drug last injected (46%), and methadone was the most commonly prescribed OAT (77%). The primary outcome was discontinuation of OAT (methadone, buprenorphine or buprenorphine-naloxone). Among respondents who reported current OAT, those who did not report current OAT in all subsequent records were defined as discontinued, and those with current OAT at all subsequent records were defined as retained. Predictors of discontinuation included self-reported demographic (sex, location, Indigenous status) and drug use characteristics (drug last injected, frequency of injection). Just fewer than one-third of respondents (29%) reported an OAT discontinuation event. The crude discontinuation rate was 6.3 [95% confidence intervals (CI)=5.9-6.8] per 100 PYO. Discontinuation was significantly higher among respondents who reported last injecting pharmaceutical opioids [adjusted hazard ratio (aHR)=1.75, 95% CI=1.41-2.17, P<0.001], being prescribed buprenorphine (aHR=1.44, 95% CI=1.18-1.76, P=0.001) or buprenorphine-naloxone (aHR=1.68, 95% CI=1.20-2.34, P=0.002), daily or more frequent injection (aHR=1.51, 95% CI=1.23-1.85, P<0.001), recent public injecting (aHR= 1.37, 95% CI=1.17-1.60, P<0.001), incarceration in the previous 12months (aHR= 1.31, 95% CI=1.05-1.64, P=0.017), recent receptive syringe or injection equipment sharing (aHR =1.28, 95% CI=1.10-1.48, P=0.001) and male sex (aHR=1.27, 95% CI=1.09-1.47, P=0.002). People who inject drugs attending needle-syringe programmes in Australia appear to be significantly more likely to discontinue opioid agonist treatment if they were prescribed buprenorphine or buprenorphine-naloxone compared with methadone, are male or report injection risk behaviours and recent incarceration.