Initiation of strong prescription opioids in Australia: cohort characteristics and factors associated with the type of opioid initiated.

Abstract

To describe the characteristics of Australians initiating strong opioids and examine the factors associated with the type of opioid initiated. Pharmaceutical Benefits Scheme dispensing records were extracted for a 10% sample of people who initiated a strong opioid treatment episode (buprenorphine, fentanyl, hydromorphone, morphine, oxycodone) between 29 September 2009 and 31 December 2013, as evidenced by the absence of a strong opioid dispensing for at least 90days. The cohort was restricted to people with complete medicines ascertainment. Socio-demographic characteristics, previous dispensing histories and index opioid use were examined. Multinomial logistic regression was used to calculate adjusted relative risk ratios (aRRRs) and 95% confidence intervals (CIs) to determine the factors associated with the type of opioid medicine initiated, relative to oxycodone. The cohort consisted of 125 335 people: 58.3% were female and 63.7% were aged ≥65years. The most commonly initiated strong opioid was oxycodone (72.8%), usually 5mg immediate-release tablets (76.1%). Compared to people aged 18-44years, those ≥85years were 14.18 times as likely (95% CI 12.67-15.87) to initiate morphine than oxycodone. Compared to people without a cancer treatment history, those with a cancer treatment history were 2.34 times as likely (95% CI 2.11-2.60) to initiate morphine than oxycodone. The most commonly initiated strong opioid was oxycodone, usually at lower strengths. Those who initiated oxycodone were more likely to be younger with no previous cancer treatment history. As these are high-risk characteristics for potential harms, a judicious approach when initiating strong opioids for this group is necessary.