Differential patterns of opioid use: defining persistent opioid use in a prescription database.

AIM: The aim of this study was to develop definitions to identify persons with clinically different patterns of persistent opioid use based on data from prescription databases.

METHODS: The study is based on data from the Norwegian Prescription Database using all dispensed opioid prescriptions during 2005-2008. Three definitions of persistent opioid use were developed using the following patient criteria: different levels of dispensed opioid amounts, number of prescriptions and the number of quarters out of the year in which prescriptions were dispensed. The three definitions each have some typical patient characteristics attached to them. The strict definition describes a typical patient using opioids to achieve a continuous serum concentration in the therapeutic range, the intermediate definition represents a typical patient using opioids daily but not around the clock and the wide definition describes a typical patient who uses opioids most of the days. To study whether the definitions accurately represent long-term use, the patient population was followed for 3 years, and the retention rate within each definition was measured.

RESULTS: The point prevalence of persistent opioid use in Norway (4,681,134 inhabitants) as defined by the strict, intermediate and wide definitions was 0.16% (n = 7663), 0.50% (n = 23,498) and 1.08% (n = 50,791), respectively, as of 31 December 2007. At the end of the 3-year study period, the retention within any of the definitions was 83%, 84% and 68% for patients who met the criteria of the strict, intermediate and wide definitions, respectively.

CONCLUSION: In the patient populations identified by the three definitions, a high rate of retention was observed, indicating that the proposed definitions can identify patients with long-term persistent use of opioids.