Effects of a β₂-agonist on airway hyperreactivity in subjects with cervical spinal cord injury

Study Objective: Aerosolized ipratropium bromide or orally administered baclofen or oxybutynin chloride (Ditropan) block methacholine-associated airway hyperreactivity in subjects with chronic cervical spinal cord injury (SCI), whereas these agents do not inhibit airway hyperreactivity associated with the inhalation of histamine. The present study was performed to determine whether pretreatment with a β₂-agonist attenuates airway hyperresponsiveness in these subjects. Participants: Subjects with chronic cervical SCI previously demonstrating airway hyperreactivity were challenged with methacholine (n = 9) or histamine (n = 16) alone and, on a separate day, 25 min following inhalation of nebulized metaproterenol sulfate. Results: Inhalation of the β₂-agonist was associated with an increase in provocative concentration causing a 20% decrease in FEV₁ (PC₂₀) values (geometric mean) from 1.01 ± 2.76 to 20.54 ± 6.24 mg/mL for methacholine and from 2.29 ± 2.26 to 19.82 ± 5.93 mg/mL for histamine. No correlation was found between specific PC₂₀ values for individual subjects and percentage improvement in FEV₁ (liter) following inhalation of metaproterenol sulfate and between PC₂₀ values and baseline FEV₁ percent. Conclusion: These data, combined with findings that patients with chronic high cervical SCI experience increased breathlessness following exposure to exogenous agents, suggest that long-term prophylactic β₂-agonist therapy may reduce respiratory symptoms associated with airway hyperreactivity in these patients.