Prescribed therapy for asthma: therapeutic ratios and outcomes

Background: Inhaled corticosteroids (ICS) are the cornerstone of asthma therapy. The ICS-to-total-asthma-medication ratios, calculated from claims data, indicate potentially risky disease management in asthma. Our aim was to assess the utility of ICS-to-total-asthma-medication ratios from primary care electronic medical records (EMRs) in detecting patients at risk of asthma exacerbation, as approached by prescription of oral corticosteroids and/or antibiotics. Methods: Retrospective cohort studies were identified, using the Health Improvement Network general practice database (THIN, United Kingdom) and the Cegedim Longitudinal Patient Data (France). We selected asthma patients aged 16-40 years, with >= 4 prescriptions for asthma medications in 2007 and >= 1 prescription in 2008. For each country, three groups were defined according to ratio value in 2008: 0% (non-ICS users), <50% (low-ICS-ratio group) and >= 50% (high-ICS-ratio group). Outcomes were marker of asthma exacerbations: systemic corticosteroids and antibiotics. They were compared between groups in each country. Results: Among 38,637 British and 4,587 French patients, higher numbers of prescriptions per patient of systemic corticosteroids, antibiotics and total asthma medications were observed in the low-ICS-ratio groups compared to other groups (p < 0.0001 for each outcome in both countries). Likewise, low-ICS-ratio patients had more medical contacts (p < 0.0001 in both countries), suggesting poorly controlled asthma. ICS-treated patients had lower risks of receiving systemic corticosteroids in 2008 in the high-ICS-ratio group, compared to the low-ICS-ratio group: RR = 0.54, 95%CI = [0.50-0.57] and RR = 0.78, 95%CI = [0.67-0.91] in the UK and France, respectively. Conclusions: Patients with high ICS-to-total-asthma-medication ratios presented fewer asthma-related outcomes. The low ICS-to-total-asthma-medication ratio calculated with EMRs data reflects insufficient prescribing of ICS relative to all asthma medications, which may lead to deteriorated asthma control.