Development of a methacholine challenge method to minimize methacholine waste

Area of Science:

• Pulmonary Medicine
• Respiratory Physiology
• Pharmacology

Background:

• Standard methacholine challenge protocols use 3 mL of solution, leading to significant drug waste.
• The conventional method involves a 2-minute tidal breathing technique with doubling concentrations.
• Optimizing methacholine challenge protocols is crucial for reducing costs and environmental impact.

Purpose of the Study:

• To develop and evaluate a modified methacholine challenge method that minimizes drug waste.
• To compare the efficacy and accuracy of the new method against the standard protocol.
• To assess the impact of reduced volume and altered concentration steps on provocative concentration results.

Main Methods:

• Twelve mild, well-controlled asthma patients participated in three randomized methacholine challenges.
• Methods included: standard 3 mL/2-min inhalation, 1.5 mL/1-min inhalation with quadrupling concentrations, and 1.5 mL/30-120s inhalations with eightfold concentration steps.
• Provocative concentration causing a 20% fall in FEV1 (PC(20)) was calculated for each method.

Main Results:

• No significant differences were observed in the geometric mean PC(20) values across the three methods (p = 0.47).
• The quadrupling concentration method using 1.5 mL was found to be less prone to error.
• Modified protocols successfully reduced methacholine waste by approximately two-thirds.

Conclusions:

• Methacholine waste can be significantly reduced by decreasing the inhaled volume to 1.5 mL.
• Utilizing quadrupling concentration steps, or sequential 1-min and 2-min inhalations, maintains diagnostic accuracy.
• These modified methacholine challenge methods offer a more efficient and potentially cost-effective alternative.