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Clinical Investigations: PULMONARY FUNCTION TEST |

Lack of Tachyphylaxis to Methacholine at 24 h*

Donald W. Cockcroft, BSc, MD, FCCP; Beth E. Davis, BSc
Author and Funding Information

Department of Medicine, Division of Respirology, Critical Care, and Sleep Medicine, University of Saskatchewan, Royal University Hospital, Saskatoon, SK, Canada.

Correspondence to: Donald W. Cockcroft, BSc, MD, FCCP, Royal University Hospital, Division of Respirology, Critical Care and Sleep Medicine, 103 Hospital Dr, Ellis Hall, Fifth Floor, Saskatoon, SK, S7N 0W8 Canada; e-mail: cockcroft@sask.usask.ca



Chest. 2005;128(3):1248-1251. doi:10.1378/chest.128.3.1248
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Objective: To examine for tachyphylaxis to methacholine at 24 h and to use these data to assess the repeatability of the provocative concentration of a substance causing a 20% fall in FEV1 (PC20) for methacholine and to obtain statistical power calculations.

Design: Retrospective review of four double-blind, placebo-controlled studies with two methacholine PC20 values measured at 24-h intervals.

Setting: Tertiary university hospital bronchoprovocation laboratory.

Patients: Thirty-two subjects with mild-to-moderate well-controlled asthma.

Interventions: The placebo arms of the four studies were examined.

Measurements: Methacholine PC20 (using 2-min tidal breathing method) initial determination and repeat testing at 24 h.

Results: The geometric mean PC20 values were 1.57 mg/mL (95% confidence interval [CI], 1.0 to 2.4 mg/mL) and 1.62 mg/mL (95% CI, 1.0 to 2.6 mg/mL NSD; p = 0.64). The mean absolute difference between the two measurements was < 0.4 doubling concentrations, and 31 of 32 measurements had both values within one doubling concentration. These data provide a statistical power of 92% for 10 subjects to show a one-half concentration ΔPC20 and a mean power of 99 ± 1% to show a one-concentration ΔPC20.

Conclusions: There is no evidence for methacholine tachyphylaxis at 24 h in subjects with asthma. At 24 h, the average repeatability was well within a one-half concentration change, and individually 31 of 32 measurements (97%) were within one doubling concentration.

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