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Dose versus concentration of methacholine.
D E Drotar1, B E Davis, D W Cockcroft
1Department of Medicine, Royal University Hospital, Saskatoon, Canada.
Summary
The dose of methacholine, not its concentration, is the main driver of bronchial response during airway hyperresponsiveness testing. This finding clarifies the methacholine challenge test
Area of Science:
- Pulmonary Medicine
- Respiratory Physiology
Background:
- The methacholine challenge test is standard for diagnosing airway hyperresponsiveness.
- Debate exists regarding whether methacholine's airway effects stem from concentration or dose.
Purpose of the Study:
- To ascertain if airway response in methacholine challenge tests is dose- or concentration-dependent.
Main Methods:
- Ten mild asthma patients underwent two methacholine challenge tests with varying inhalation durations (30 seconds vs. 2 minutes).
- Tests were randomized and conducted within a week, ensuring comparable daily conditions.
Main Results:
- The geometric mean PC20 (provocative concentration causing 20% fall in FEV1) was significantly higher with 30-second inhalations (5.7 mg/mL) versus 2-minute inhalations (1.1 mg/mL).
- Statistical analysis showed no significant difference when comparing the 2-minute PC20 multiplied by 4 to the 30-second PC20, supporting dose-dependency.
Conclusions:
- Methacholine's bronchial effect is primarily determined by the administered dose, not solely its concentration.
- This clarifies the mechanism underlying airway hyperresponsiveness detected via methacholine challenge testing.