Opioid use frequency in early axial spondyloarthritis in Finland - a pharmacoepidemic register study.

Objectives: To evaluate opioid use among incident axial spondyloarthritis (axSpA) patients compared to general population.

Methods: From the national register, we identified all adult patients with axSpA (ICD-10 codes M45-46), who between 2010 and 2014 (index date, ID) were for the first time granted special reimbursement for any disease-modifying antirheumatic drugs (DMARDs). Three matched population controls were identified for each patient. Drug purchases were evaluated between 2009-2015, and opioid use was analyzed for one year before and after the ID. The Defined Daily Dose (DDD) was used as a tool to assess the opioid consumption before and after the biological (b) DMARD initiation.

Results: We identified 3577 axSpA patients and 10,573 controls. Of these patients, 97.2% started a conventional synthetic (cs) DMARD during a year after ID and 23.4% switched later to a self-injected bDMARD between the ID and 31 Dec 2015 (median follow-up 3.4 years). Opioids were purchased at least once by 29.8% and 21.7% of the patients in the years before and after the ID, respectively, compared to 8.1% and 7.8% of the controls. The proportion of opioid-using patients was greatest during the last quarter before the ID [relative risk (RR) 4.72 (95% CI 4.14 to 5.39)] compared to controls, and it remained higher [RR 2.84 (2.59 to 3.11)] also after the start of csDMARDs. DDD of opioid consumption decreased from 7.7 to 1.6/1000 inhabitants after bDMARD initiation.

Conclusion: Considerably more axSpA patients than population controls used opioids. The opioid consumption by dose decreased clearly after bDMARD initiation.