Duration of opioid use and association with socioeconomic status, daily dose and formulation: a two-decade population study in Queensland, Australia.

Background There is an association between the duration of prescription opioids use and an increased risk of serious harm, often unintentional. Objective (1) Describe the trends in duration of prescription opioids dispensing and, (2) determine the risk of long-term use (≥4 months) based on patients' socioeconomic status, daily dose in oral daily morphine milligram equivalent, and opioid formulation. Setting Residents of Queensland (2,827,727), Australia from the age 18 years and who were dispensed pharmaceutical opioids from 1 January 1997 to 31 December 2018. Method Retrospective, longitudinal population-based analysis using data obtained from the Monitoring of Drugs of Dependence system of the Monitored Medicines Unit of Queensland Health. Main outcome measure Contribution of socioeconomic status, and daily dose and opioid formulation (modified-release or immediate-release) to the risk of long-term opioid use. Results There was little difference between the number of patients dispensed opioids for ≥4 months and ≤3 months between 1997 and 2011. Thereafter, the number for those using opioids long-term increased. The highest risk of having opioids dispensed for ≥4 months were for patients in the lowest level of socioeconomic status (adjusted odds ratio 1.36; 95% CI, 1.34, 1.38), compared to people in the highest socioeconomic status areas, followed by the low-socioeconomic status areas, mid-socioeconomic status areas, and high-socioeconomic status areas respectively. The risk of being dispensed prescription opioids for ≥4 months significantly increased as the dose increased: adjusted odds ratio 1.73; 95% CI, 1.71, 1.75, adjusted odds ratio 1.89; 95% CI, 1.87, 1.92, and adjusted odds ratio 3.63; 95% CI, 3.58, 3.69 for the ≥20 to <50 oral daily morphine milligram equivalent, ≥50 to <100 oral daily morphine milligram equivalent and ≥100 oral daily morphine milligram equivalent dose categories, respectively. Conclusion Higher doses and living in a low socioeconomic status areas were associated with increased risk of long-term dispensing of opioid prescriptions.