Background: Little is known about adherence to inhaled medication in COPD and the impact on mortality and morbidity.
Methods: We used data on drug adherence from a randomised, double-blind trial comparing inhaled salmeterol 50μg+fluticasone propionate 500μg bid with placebo and each drug individually in 6112 patients with moderate-severe COPD over 3 years in the TORCH study. All-cause mortality and exacerbations leading to hospital admission were primary and secondary endpoints. The study of adherence was not specified a priori as an ancillary study.
Results: Of the 4880 patients (79.8%) with good adherence defined as >80% use of study medication, 11.3% died in contrast to 26.4% among the 1232 patients (20.2%) with poor adherence. The annual rates of hospitalisation for exacerbations were 0.15 and 0.27, respectively. The association between adherence and mortality remained unchanged and statistically significant after adjusting for other factors related to prognosis with a hazard ratio 0.40 (95% confidence interval 0.35 -0.46), p<0.001). The association was even stronger when analysing on-treatment deaths only. Similarly, the association between adherence and hospitalisation remained unchanged and significant in a multivariate analysis, rate ratio 0.58 (95% confidence interval 0.44-0.73, p<0.001). The association between increased adherence and improved mortality and reduction in hospitalisation was independent of study treatment. The effect of treatment was more pronounced in patients with good adherence than in those with poor adherence.
Conclusion: Adherence to inhaled medication is significantly associated with reduced risk of death and hospitalisation due to exacerbations in COPD. Further research is needed to understand these strong associations.