Initial opioid prescription characteristics and risk of opioid misuse, poisoning and dependence: retrospective cohort study.

OBJECTIVE: To identify individual and initial prescription-related factors associated with an increased risk for opioid-related misuse, poisoning and dependence (MPD) in patients with non-cancer pain. METHODS: Cohort study linking several databases covering 5 million inhabitants of the region of Valencia, Spain, including all adults initiating prescription opioids in the period 2012-2018. To ascertain the association between the characteristics of the initial prescription choice and the risk of opioid MPD, we used shared frailty Cox regression models. We additionally considered death as a competing risk in sensitivity analyses. RESULTS: 958 019 patients initiated opioid prescription from 2012 to 2018, of which 0.13% experienced MPD. Most patients were prescribed tramadol as initial opioid (76.7%) followed by codeine (16.3%), long-acting opioids (6.7%), short-acting opioids (0.2%) and ultrafast opioids (0.1%). Initiation with ultrafast (HR 7.2; 95% CI 4.1 to 12.6), short-acting (HR 4.8; 95% CI 2.3 to 10.2) and long-acting opioids (HR 1.5; 95% CI 1.2 to 1.9) were associated with a higher risk of MPD when compared with tramadol. Initial prescriptions covering 4-7 days (HR 1.3; 95% CI 1.0 to 1.8), 8-14 days (HR 1.4; 95% CI 1.0 to 1.9), 15-30 days (HR 1.7; 95% CI 1.2 to 2.3) and more than one a month (HR 1.8; 95% CI 1.3 to 2.5) were associated with more MPD risk than initial prescriptions for 1-3 days. Treatments with >120 daily morphine milligram equivalents (MME) increased MPD risk (vs <50 MME, HR 1.6; 95% CI 1.1 to 2.2). Main individual factors associated with increased risk of MPD risk were male sex (HR 2.4; 95% CI 2.1 to 2.7), younger age (when compared with patients aged 18-44 years, patients aged 45-64 years, HR 0.4; 95% CI 0.4 to 0.5; patients aged 65-74 years, HR 0.4; 95% CI 0.3 to 0.5 and patients aged 75 years old and over, HR 0.7; 95% CI 0.6 to 0.8), lack of economic resources (2.1; 95% CI 1.8 to 2.5) and registered misuse of alcohol (2.9; 95% CI 2.4 to 3.5). Sensitivity analyses yielded overall comparable results. CONCLUSIONS: Our study identifies riskier patterns of opioid prescription initiation for non-cancer indications, as well as patient subgroups with higher risk of misuse, poisoning and dependence.