Medication Use Trajectories in Chronic Pain: Comparing Risk-Based and Count-Based Approaches Using Linked Prescription Claims Data

IntroductionIn the context of chronic pain, no study has yet compared risk-based and count-based approaches for modelling medication use trajectories. Risk-based approach reflects the potential burden of medication-related adverse effects, whereas count-based approach reflects treatment burden and regimen complexity. Comparing these complementary measures may identify different patient profiles depending on the clinical or research objective. ObjectivesThis study aimed to compare a composite medication risk score, the Medication Quantification Scale 4.0 (MQS-4.0), with medication count in examining medication use trajectories among individuals with chronic pain. MethodsWe conducted a cohort study using data from the TorSaDE Cohort, which links five cycles of Statistics Canada's Canadian Community Health Survey (2007-2016 cross-sectional questionnaires) and Québec provincial health administrative databases (1996-2016 longitudinal data). We selected 8,760 adults with chronic pain who were covered by public prescription drug insurance. Pain-related medications used in the two-year period following survey completion were operationalised as monthly risk scores and monthly medication count. Growth Mixture Modelling was applied to each of these measures to identify groups with similar patterns over time (trajectories). ResultsBoth the MQS-4.0 risk score and the medication count were effective in forming trajectory groups that were statistically robust (based on entropy and Bayesian information criterion) and clinically meaningful. However, the MQS-4.0 risk score approach was more discriminative, identifying differences between trajectory groups in terms of sociodemographic characteristics, pain profiles, health status, and healthcare utilisation. Individuals with the highest pain-related medication count did not necessarily have the highest MQS-4.0 risk scores, and some individuals using fewer medications were found to be at high risk. ConclusionsOur findings suggest that a risk-based approach such as the MQS-4.0 may provide complementary information to a count-based approach for subgroup analyses, particularly when using health administrative databases to study pain-related medication use in individuals living with chronic pain.