To what extent do data from pharmaceutical claims under-estimate opioid analgesic utilisation in Australia?

Although pharmaceutical claims are an essential data source for pharmacoepidemiological studies, these data potentially under-estimate opioid utilisation. Therefore, this study aimed to quantify the extent to which pharmaceutical claims from Australia's national medicines subsidy programs (Pharmaceutical Benefits Scheme [PBS] and Repatriation Schedule of Pharmaceutical Benefits [RPBS]) under-estimate prescription-only and total national opioid utilisation across time and for different opioids. A secondary aim was to examine the impact of the 2012 policy change to record all PBS/RPBS dispensed medicines, irrespective of government subsidy, on the degree of under-estimation.

Aggregated data on Australian opioid utilisation were obtained for the 2010 to 2014 calendar years, including all single ingredient and combination opioid analgesic preparations available on prescription or over-the-counter (OTC). Total opioid utilisation (oral morphine equivalent kilogrammes) was quantified using sales data from IMS Health and compared with pharmaceutical claims data from the PBS/RPBS.

PBS/RPBS claims data did not account for 12.4% of prescription-only opioid utilisation in 2014 and 19.1% in 2010, and 18.4% to 25.4% of total opioid use when accounting for OTC preparations. Between 2010 and 2014, 5.6% to 5.3% of buprenorphine, 8.1% to 6.3% fentanyl, 17.7% to 10.7% oxycodone, 18.4% to 11.0% tramadol, 38.4% to 21.0% hydromorphone, and 28.6% to 21.0% of prescription-only codeine utilisation were not accounted for in PBS/RPBS claims.

Despite increased capture of less expensive (under co-payment) opioid items since 2012, PBS/RPBS claims still under-estimate opioid use in Australia, with varying degrees across opioids. The estimates generated in this study allow us to better understand the degree of under-estimation and account for these in research using Australia's national pharmaceutical claims data.