Impact of income-based public drug coverage deductibles on adherence to asthma medications

Background: Cost-related nonadherence to medications can be a barrier to asthma management. Objective: To quantify the impact of public drug plan deductibles on adherence to asthma medications. Methods: We used a quasi-experimental regression discontinuity analysis to determine whether thresholds in deductibles for public drug coverage, determined on the basis of annual household income, decreased medication use among lower-income children and adults with asthma in British Columbia from 2013 to 2018. Using dispensed medication records, we evaluated deductible thresholds at annual household incomes of $15,000 (a deductible increase from 0% to 2% of annual household income), and $30,000 (a deductible increase from 2% to 3% annual household income). We evaluated medication costs, use, the ratio of inhaled corticosteroids containing controller medications to total medications, excessive use of short-acting beta-agonists, and the proportion of days covered by controller therapies. All costs are reported in 2020 Canadian dollars. Results: Overall, 88,935 individuals contributed 443,847 person-years of follow-up (57% of female sex, mean age 31 years). Public drug subsidy decreased by -$41.74 (95% CI, -$28.34 to -$55.13) at the $15,000-deductible threshold, a 28% reduction, and patient costs increased by $48.45 (95% CI, $35.37-$61.53). The $30,000 deductible threshold did not affect public drug costs (P =.31), but patient costs increased by $27.65 (95% CI, $15.22-$40.09), which is an 11% increase. Asthma-related medication use, inhaled corticosteroids to total medication ratio, excessive use of short-acting beta-agonists, and proportion of days covered by controller therapies were not impacted by deductible thresholds. Conclusion: Income-based deductibles reduced public drug costs with no effect on asthma-related medication use, adherence to controller therapies, or excessive reliever therapy use in lower-income individuals with asthma. (c) 2023 American College of Allergy, Asthma & Immunology. Published by Elsevier Inc. All rights reserved.