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.