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Rebuttal from Dr. O'Byrne

St. Joseph's Hospital and McMaster University, Hamilton, Ontario, Canada

Inhaled corticosteroids are effective in mild persistent asthma. All studies which have studied mild asthma agree on this. Dr. Boushey does not dispute this fact in three of the four domains, where improvement could be measured. Lung function is improved, as measured by prebronchodilator FEV₁ in all studies. This is the most appropriate measure of lung function in this population, as the postbronchodilator measurement provides little room for improvement. Symptoms are also improved, as are markers of airway inflammation.

The only important domain where the IMPACT study differs from the others is in the frequency of exacerbations. The reasons for this are that, in contrast to OPTIMA and START, asthma exacerbations were not a primary variable in IMPACT and the study was not designed to examine this outcome. Second, the rate of exacerbations in IMPACT was much lower than in the other studies. This may be due to the fact that all patients received an intensive therapy with prednisone and high-dose budesonide and zafirlukast for 10 to 14 days before being allocated to blinded treatment (not a treatment approach that many physicians would consider for patients with mild persistent asthma). It is plausible that this had an important effect in reducing exacerbation rates, even for the duration of the study. This was done because the study question originally asked was related to the decline in lung function over time, and not the effects of regular treatment with low-dose ICS on asthma exacerbations. Thus, the IMPACT study can make no useful statement with regards to the effects of regular ICS treatment on asthma exacerbations, which is likely the main reason that they would be recommended in this population with near-normal lung function and relatively infrequent symptoms.

The economic argument made by Dr. Boushey is likely correct, if low-dose inhaled budesonide does not have a major impact on reducing exacerbations in mild persistent asthma. As this conclusion of the IMPACT trial is implausible (given that every other study that has examined the effect of ICS on asthma exacerbations has shown a clinically important effect) and likely wrong, the economic argument does not hold up, as asthma exacerbations have an enormous economic burden attached to them.

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