Cost saving of switching to equivalent inhalers and its effect on health outcomes

Background Switching inhalers to cheaper equivalent products is often advocated as a necessary cost saving measure, yet the impact on patient’s health and healthcare utilisation has not been measured. Methods We identified asthma and chronic obstructive pulmonary disease (COPD) patients from UK primary care electronic healthcare records between 2000 and 2016. A self-controlled case series was used to estimate incidence rate ratios (IRR); comparing outcome rates during the risk period, 3-months after the exposure (financially-motivated switch), and control periods (pre-switch, and post-risk period). Four outcomes were assessed: disease exacerbation, GP consultation, non-specific respiratory events and adverse-medication events. Medication possession ratio (MPR) was calculated to assess adherence. 2017 NHS indicative prices were used to estimate cost differences per equivalent dose. Results We identified a cohort of 569,901 asthma and 171,231 COPD regular inhaler users, 2% and 6% had been switched, respectively. Inhaler switches between a brand-to-generic inhaler, and all other switches (brand-to-brand, generic-to-generic, generic-to-brand), were associated with reduced exacerbations (brand-to-generic: IRR=0.75, 95% CI 0.64-0.88; all other: IRR=0.79, 95% CI 0.71-0.88). Gender, age, therapeutic class, inhaler device, and inhaler-technique checks did not significantly modify this association (p<0.05). The rate of consultations, respiratory-events and adverse-medication events did not change significantly (consultations: IRR=1.00, 95% CI 0.99-1.01; respiratory-events: IRR=0.96, 95% CI 0.95-0.97; adverse-medication-events: IRR=1.05, 95% CI 0.96-1.15). Adherence significantly increased post-switch (median MPR: pre-switch=54%, post-switch=62%; p