Characteristics of patients with asthma overprescribed short- acting beta- agonist (SABA) reliever inhalers stratified by blood eosinophil count in North East London: a cross- sectional observational study

Background: Overprescription of short-acting beta-agonist (SABA) inhalers and blood eosinophil count have strong associations with exacerbation risk in asthma. However, in the authors' recent publication only a minority of patients overprescribed SABA (>= 6 inhalers in 12 months) were eosinophilic (>= 0.3 x 10(9) cells/l).Aim: To compare the characteristics of eosinophilic and non-eosinophilic patients with asthma overprescribed SABA inhalers, and identify latent classes using clinical variables available in primary care.Design & setting: Cross-sectional analysis of patients with asthma in North East London, England, using primary care electronic health record data.Method: Unadjusted and adjusted multi-variate regression models and latent class analysis.Results: Eosinophilia was significantly less likely in female patients (P = 0.004), those with multiple mental health comorbidities (P<0.001), and those with SABA on repeat prescription (P<0.001). Latent class analysis identified the following three classes of patients overprescribed SABA: class 1, which represents classical uncontrolled asthma (oral steroids required for exacerbations, step 2-3 asthma medications, high probability of being eosinophilic); class 2, which represents mild asthma (low exacerbation frequency, low asthma medication step, low probability of being eosinophilic); and class 3, which represents difficult asthma (high exacerbation frequency despite high-strength preventer inhalers, low probability of being eosinophilic). The mild asthma class was the largest.Conclusion: Many patients being overprescribed SABA were non-eosinophilic with a low exacerbation frequency, suggesting disproportionately high SABA prescription compared with other asthma control markers. Potential reasons for high SABA prescription in these patients included repeat prescription (being dispensed but not taken) and use of SABA for non-asthma breathlessness (for example, breathing pattern disorders with anxiety). Further research is needed into management of SABA overuse in patients without other markers of uncontrolled asthma.