Time intervals (3' or 5') between dose steps can influence methacholine challenge test.

Bronchial hyperresponsiveness (BHR) is a common feature in the majority of asthmatic subjects and methacholine is the most frequently used agent for the test. The influence of 3 or 5 min time intervals between doses steps in a double methacholine challenge test (MCH-3′ or MCH-5′) was investigated. Using the MCH-3′ challenge, 52 intermittent asthmatics were classified as having moderate (BHR-M; 18 subjects), mild (BHR-m; 19 subjects), or bordeline (BHR-B; 15 subjects) BHR. The cumulative dose and the PD20FEV1 were higher for MCH-5′ compared with MCH-3′ in BHR-m (p < 0.05) and BHR-B (p < 0.05) but not in the BHR-M group. Also the dose response slopes, FEV1% decline/cumulative methacholine dose, calculated for the two challenge tests were statistically different only in BHR-m (p < 0.05) and BHR-B (p < 0.01). At MCH-5′, there were 16 subjects with BHR-M, 18 with BHR-m, 12 with BHR-B and 6 subjects with normal reactivity. Results may suggest that in the group of BHR-m and BHR-B subjects, at MCH-5′ compared with MCH-3′, the cumulative effect of the administered drug, quickly metabolized by cholinesterase, is not complete, thus leading to an incorrect estimation of bronchial hyperresponsiveness degree. It is hoped that time interval between doses be standardized to ensure maximum comparability within and between subjects in challenge tests.