title: Provocative dose of methacholine causing a 20% drop in FEV1 should be used to interpret methacholine challenge tests with modern nebulizers.
abstract: BACKGROUND
  The American Thoracic Society guidelines (1999) for methacholine challenge tests (MCTs) using the 2-minute tidal breathing protocol were developed for the now-obsolete English-Wright (EW) nebulizer. In addition, the guideline recommendation to use the provocative concentration of methacholine causing a 20% drop in FEV1 (PC20) rather than the provocative dose of methacholine causing a 20% drop in FEV1 (PD20) for determining the level of bronchial hyperresponsiveness has been challenged.
  
  
  OBJECTIVE
  To determine if cumulative dose or concentration of methacholine delivered to the airways is the determinant for airway responsiveness and to validate use of the AeroEclipse* II BAN (Aero; Trudell Medical International, London, ON, Canada) nebulizer compared with use of the reference standard EW nebulizer.
  
  
  METHODS
  Subjects with asthma (10-18 yr old) participated in randomized, controlled cross-over experiments comparing four MCT protocols using standard methacholine concentrations, but varying: (1) methacholine starting concentration (testing for cumulative effect); (2) nebulizer (EW versus Aero); and (3) inhalation time. PD20 was calculated using nebulizer output rate, inhalation time, and preceding doses delivered. ANOVA analyses were used to compare geometric means of PC20 and PD20 between protocols.
  
  
  RESULTS
  A total of 32 subjects (17 male) participated. PC20 differed when starting concentration varied (0.46 vs. 0.80 mg/ml; P<0.0001), whereas PD20 did not (0.06 vs. 0.08 mg). PC20 differed with the EW versus the Aero nebulzer with 30-second inhalation (1.19 vs. 0.43 mg/ml; P=0.0006) and the EW versus the Aero nebulizer with 20-second inhalation (1.91 vs. 0.89 mg/ml; P=0.0027), whereas PD20 did not (0.07 vs. 0.06 mg and 0.11 vs. 0.09 mg, respectively).
  
  
  CONCLUSIONS
  In MCTs, the cumulative dose (PD20), not the PC20, determines bronchial responsiveness. Modern nebulizers may be used for the test if clinical interpretation is based on PD20. Clinical trial registered with www.clinicaltrials.gov (NCT01288482).
authors.affiliation: 1 Division of Respiratory Medicine, and.
authors.forename: Sharon D
authors.initials: SD
authors.lastname: Dell
authors.forename: Sundeep S
authors.initials: SS
authors.lastname: Bola
authors.forename: Richard G
authors.initials: RG
authors.lastname: Foty
authors.forename: Laura C
authors.initials: LC
authors.lastname: Marshall
authors.forename: Kathleen A
authors.initials: KA
authors.lastname: Nelligan
authors.forename: Allan L
authors.initials: AL
authors.lastname: Coates
mesh_terms: D000280:Administration, Inhalation; D000293:Adolescent; D001249:Asthma / Q000175:diagnosis* / Q000503:physiopathology; D016535:Bronchial Hyperreactivity / Q000175:diagnosis* / Q000503:physiopathology; D001985:Bronchial Provocation Tests; D016085:Bronchoconstrictor Agents / Q000008:administration & dosage; D002648:Child; D002675:Child, Preschool; D018592:Cross-Over Studies; D004305:Dose-Response Relationship, Drug; D005260:Female; D005500:Follow-Up Studies; D005541:Forced Expiratory Volume / Q000187:drug effects*; D006801:Humans; D008297:Male; D016210:Methacholine Chloride / Q000008:administration & dosage*; D009330:Nebulizers and Vaporizers
chemical_list: D016085:Bronchoconstrictor Agents; D016210:Methacholine Chloride
keywords: asthma; bronchial hyperreactivity; diagnosis; methacholine; nebulizers