Dose versus concentration of methacholine.

BACKGROUND

The methacholine challenge test is a common investigation used to identify airway hyperresponsiveness. There has been recent debate as to whether the airway effect is due to the concentration or the dose of methacholine.

OBJECTIVE

To determine whether the airway response during a methacholine challenge test is due to the concentration or the dose of methacholine.

METHODS

Ten subjects with stable, mild asthma were enrolled in this study. Two methacholine challenge tests, one with 30-second inhalations of methacholine and the other with two minute inhalations of methacholine, were performed on each subject in a random order on 2 days within a 1-week period at approximately the same time each day.

RESULTS

The geometric mean 2-minute PC20 was 1.1 mg/mL and the geometric mean 30-second PC20 was 5.7 mg/mL, 5.2-fold greater than the mean 2-minute PC20. The paired t-test comparison of the 2-minute PC20 multiplied by 4 and the 30-second PC20 revealed no significant difference (P > .2).

CONCLUSIONS

The dose of methacholine is primarily responsible for the degree of bronchial response rather than the concentration.