Estimating the proportion of prescription opioids that is consumed by people who inject drugs in Australia

Introduction and aims: To estimate the contribution that people who inject drugs (PWID) make to population-level use of prescription opioids in Australia. Design and methods: Data on prescriptions of oxycodone, morphine and methadone tablets were obtained for New South Wales, Victoria, Tasmania, and Queensland, and time series analyses used to characterise the trends from 2002-2010. Estimates of the number of PWID were combined with data on their levels, frequency and typical doses of morphine, methadone tablet (only prescribed in Australia for pain) and oxycodone from 2004 to 2010. Estimated consumption per 1,000 PWID and per 1,000 persons 20-69 years were contrasted; and the proportion of total consumption accounted for by PWID estimated. Results: Morphine prescribing declined; oxycodone prescribing increased. PWID had far higher rates of prescription opioid consumption (DDDs per 1,000) than the general population. Tasmania had highest use of prescribed opioids. PWID contribution to morphine consumption in Tasmania increased to 28% (range 22-37%) in 2010; elsewhere, PWID contribution was lower (midpoints of 2-12%, 2010). Methadone tablet use was less elevated compared to the general population. With the exception of Tasmania, PWID were estimated to consume less than 5% of oxycodone. Discussion and conclusions: PWID use prescription opioids at high levels and can account for a significant proportion of consumption. Increased oxycodone prescribing in Australia has not been driven by PWID. Opioid substitution therapy and other effective treatments need to be more available and attractive to PWID.