According to a recent study, commonly used inhaled corticosteroids (ICSs) for asthma can be detected in the blood for up to 8 hours, and thus are useful in measuring adherence levels of ICSs in severe asthma patients.

The key findings were as follows:

• Eight hours post inhalation, all patients using budesonide and beclomethasone dipropionate, and all but 1 using fluticasone propionate, had detectable serum drug levels.
• Low adherence by repeat prescription records (<80%) was identified in 43% of patients.
• Blood ICSs levels correlated negatively with exacerbation rate, and (for fluticasone propionate only) positively with Forced Expiratory Volume (FEV1 %) predicted.

Thus, commonly used ICSs can be used as a measure of adherence in severe asthma. In case of fluticasone propionate, higher exacerbation rates and poorer lung function were associated with lower blood ICSs levels.