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Hospital Universitario Dr Peset, Valencia, Spain
Correspondence to: Luis Prieto, MD, PhD, Seccion de Alergologia, Hospital Universitario Dr Peset, C/ Gaspar Aguilar 90, 46017 Valencia, Spain; e-mail: prieto_jes{at}gva.es
To the Editor:
We would like to thank Dr. Proietti and colleagues for their interest and stimulating comments on our article.1 We certainly agree with them that an alternative analysis utilizing a cut-off point of three doubling concentrations decrease in the provocative concentration causing a 20% fall in FEV1 (PC20) with adenosine 5'-monophosphate (AMP) 2 weeks after halving the dose of inhaled corticosteroids (ICS) would provide different results. However, only one of our patients showed a decrease in PC20 of three or more doubling concentrations 2 weeks after the dose of ICS was halved.
Dr Proietti states that, "by arbitrarily setting the cut-off values for PC20 AMP at baseline too high (400 mg/mL), there is the chance of including very mild asthmatic patients who are unlikely to develop exacerbations." We regret that our description of patient characteristics has led to misunderstanding. Our study examined the utility of the determination of airway responsiveness to AMP and exhaled nitric oxide levels as markers for safely reducing the dose of ICS. Thus, we selected patients with stable asthma in good control with ICS, but not subjects with mild asthma. Although asthma control is often used to define asthma severity, this assumption is incorrect.2 A significant proportion of patients included in our study had moderate-to-severe asthma, but were well controlled with ICS at medium-to-high doses (beclomethasone, 500 to 1,000 µg or equivalent daily).
Finally, Proietti et al state that it could have been of critical importance to include methacholine provocation in the protocol. In a previous study,3 we have shown that the detection of a plateau on the concentration-response curve to methacholine, but not the PC20 value, may be used as a marker for safely reducing the corticosteroid dose. However, it is clear that further studies are needed to clarify the potential value of the determination of the response to both methacholine and AMP as a means to identifying those asthmatic patients whose conditions will or will not deteriorate when the dose of ICS is reduced.
References
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