The feasibility of airways hyperresponsiveness as an inclusion criterion for studies on childhood asthma

The feasibility of moderately severe airway hyperresponsiveness (AH) was examined as an inclusion criterion for clinical trials in asthmatic children. During the baseline period of a long-term clinical trial in asthmatic children, maintenance therapy with fluticasone (200 mug(.)day(-1)) was stopped for a maximum of 8 weeks and methacholine challenges were performed at 2-week intervals or earlier if the patients' condition deteriorated. Patients were eligible to continue the study if the provocative dose of methacholine causing a 20% fall in forced expired volume in one second (FEV1) (PD20) was <80 mug. Fifty-one per cent of the children did not develop a PD20 <80 mug after withdrawal of fluticasone. Patients with or without a PD20 <80 mug did not differ in duration of asthma, duration of treatment, or peak flow variation. Patients with a PD20 <80 mug had higher levels of total and specific immunoglobulin-E, and lower levels of FEV1 and mean maximal expiratory flow than patients with a PD20 greater than or equal to 80 mug. Forty-four per cent of the patients with a PD20 greater than or equal to 80 mug did not have any symptoms during the wash-out period and 39% of these patients remained free from symptoms during one year followup. The results of this study suggest that recruiting asthmatic children for clinical trials may be difficult if airways hyperresponsiveness is used as the sole inclusion criterion.