Effect of Dexamethasone and Fluticasone on Airway Hyperresponsiveness in Horses With Inflammatory Airway Disease

Background: Airway hyperresponsiveness (AWHR), expressed as hypersensitivity (PC75RL) or hyperreactivity (slope of the histamine dose-response curve), is a feature of inflammatory airway disease (IAD) or mild equine asthma in horses. Glucocorticoids are used empirically to treat IAD. Objectives: To determine whether dexamethasone (DEX) (0.05 mg/kg IM q24h) and inhaled fluticasone (FLUT) (3,000 mu g q12h) administered by inhalation are effective in decreasing AWHR, lung inflammation, and clinical signs in horses with IAD. Methods: A randomized crossover study design was used. Eight horses with IAD were assigned to a treatment group with either DEX or FLUT. Measured outcomes included lung mechanics during bronchoprovocative challenges, bronchoalveolar lavage fluid (BALF) cytology, and scoring of clinical signs during exercise. Results: Dexamethasone and FLUT abolished the increase in R-L by 75% at any histamine bronchoprovocative dose in all horses after the first week of treatment. However, after 2 weeks of FLUT treatment, 1 horse redeveloped hypersensitivity. There was a significant decrease in the number of lymphocytes after treatment with both DEX and FLUT (P =.039 for both) but no significant differences in other BALF cell types or total cell counts (P > .05). There was no difference in the scoring of the clinical signs during each treatment and washout period (P > .05). Conclusions and Clinical Importance: Both DEX and FLUT treatments significantly inhibit airway hypersensitivity and hyperreactivity in horses with IAD. There are no significant effects on the clinical signs or the number of inflammatory cells (except lymphocytes) in BALF. The treatments have no residual effect 3 weeks after discontinuation.