Asthma is often difficult to control and it is likely that not all patients are optimally treated.

This study aimed to explore asthma control in adults receiving fixed dose combination (FDC) therapy. Control of asthma was assessed using the mannitol challenge test as a monitoring tool to see if this would give additional information compared to the asthma control test (ACT). The study was an open-label, prospective study on 98 adults prescribed with FDC therapies for at least three months.

74 patients considered that their asthma was well controlled. However, 60 patients had a positive mannitol challenge test (PD15 < 635 mg), and when those with a positive response to the short-acting β₂-agonist (≥15%) after the mannitol challenge test were included, this increased to 64 patients (65%). Exploratory analysis determined that the spirometry parameters; FEV₁/FVC and FEV₁% of predicted, were statistically significant predictors of a positive mannitol challenge test. Co-morbid conditions such as concomitant upper airway involvement or eczema did not predict mannitol reactivity.

Although most patients rated their asthma as well controlled, many provided a positive mannitol challenge test, suggesting the presence of underlying inflammation, despite treatment with fixed dose combination therapy.

This study indicates that many asthma patients on fixed dose combination therapy may not be optimally treated.