Injection of medications used in opioid substitution treatment in Australia after the introduction of a mixed partial agonist-antagonist formulation

Abstract

Objectives: To examine the levels and predictors of injection of buprenorphine-naloxone (BNX)--a combination of a partial opioid agonist and an opioid antagonist for treating opioid dependence--which was specifically developed to limit injecting. Comparison was made with injecting of two other opioid substitution treatment medications, methadone and buprenorphine (BPN); severe harms have been documented after injection of the latter.

Design and participants: Injecting was studied in regular injecting drug users ("IDUs") and current opioid substitution treatment clients ("clients"). Regular IDUs are interviewed annually in each Australian capital city (about 900 per year) and data for 2003-2007 were used; 399 clients were interviewed in 2007. Data on injection of opioid substitution treatment medications between 2003 and 2007 were adjusted for availability of medications (from national sales data for methadone, BPN and BNX). Predictors of injecting were analysed by multiple regression analyses.

Setting: Capital cities of all Australian states and territories.

Main outcome measure: Injection of opioid substitution treatment medications among individuals both in and out of treatment.

Results: In the year after its introduction in Australia, BNX was injected less frequently and by fewer regular IDUs and clients compared with BPN, particularly when differences in the availability of medications were taken into account. Some individuals did nonetheless regularly inject BNX. Injection of methadone, BPN and BNX was more likely to occur among those injecting other pharmaceutical opioids.

Conclusions: A partial opioid agonist-antagonist combination appears to be less commonly and less frequently injected by clients in treatment and IDUs who are not. Further studies are needed to evaluate longer-term trends in use and harms.