Impact of the COVID-19 Pandemic on Adherence to Most Costly Chronic Disease Medications in British Columbia, Canada: A Population-Based Interrupted Time Series Analysis

Nevena Rebić,1,2 Eric C Sayre,3 Michael R Law,4,5 Jacquelyn J Cragg,1 Lori A Brotto,6 Mary A De Vera1,2 1Faculty of Pharmaceutical Sciences, University of British Columbia, Vancouver, BC, Canada; 2Centre for Health Evaluation and Outcome Sciences, Vancouver, BC, Canada; 3British Columbia Centre on Substance Use, Vancouver, BC, Canada; 4School of Population and Public Health, University of British Columbia, Vancouver, BC, Canada; 5Centre for Health Services and Policy Research, University of British Columbia, Vancouver, BC, Canada; 6Department of Obstetrics and Gynaecology, University of British Columbia, Vancouver, BC, CanadaCorrespondence: Mary A De Vera, University of British Columbia Faculty of Pharmaceutical Sciences, 2405 Wesbrook Mall, Vancouver, BC, V6T 1Z3, Canada, Tel +604-827-2138, Fax +604-827-2382, Email [email protected]: To address limited population-level data on prescription medication taking during COVID-19, we assessed the impact of the pandemic on adherence to the costliest drug classes prescribed for chronic diseases in British Columbia (BC).Patients and Methods: Of the 100 top drug classes contributing to total drug spending in 2020, we categorized those prescribed for chronic diseases into 26 drug groups; specifically, drugs for psychiatric and neurologic, cardiac and respiratory, hormone-related, and immune and musculoskeletal conditions. Using administrative health data on all dispensed medications, we quantified adherence by monthly proportion of days covered (PDC) and performed interrupted time-series analysis (ITS) to estimate changes in PDC trends 1-year before and after the implementation of pandemic mitigation measures.Results: We included 3,906,377 adults with ≥ 1 prescription to ≥ 1 included drug groups. The most common prescriptions among our study population were for antidepressants (45.0%), drugs for obstructive airway diseases (41.6%), renin-angiotensin system agents (30.5%), diuretics (28.2%), and lipid modifying agents (24.8%). ITS models for 22 of 26 drug groups showed statistically significant changes in monthly PDC trends, with the greatest change occurring among parenteral immunosuppressants, injectable insulins and analogues, and renin-angiotensin system agents.Conclusion: Findings suggest that the pandemic did not substantially impact adherence to commonly used medications; however, adherence was found to be suboptimal across all drug groups regardless of the impact of COVID-19. Medication adherence remains a critical therapeutic challenge requiring our attention irrespective of major healthcare system stressors such as COVID-19.Keywords: medication adherence, chronic conditions, interrupted-times series analysis, COVID-19, administrative health data