Abstract
BACKGROUND: A study reported low systemic availability of injectable dexamethasone nebulized to healthy horses using the Flexineb mask. When used in horses with severe asthma and a different nebulizer, lack of efficacy and cortisol suppression were observed. HYPOTHESIS: Nebulized dexamethasone is as effective as PO administration for the treatment of severe asthma in horses. ANIMALS: Twelve horses with severe asthma from a research herd. METHODS: Randomized clinical trial. Horses were divided into 2 groups and received 5 mg of dexamethasone sodium phosphate by nebulization using a Flexineb mask (NE, n = 6) or PO (OR, n = 6) q24h for 7 days. Lung function and serum cortisol concentrations were evaluated at baseline, after 4 days of treatment (D4) and 1 day after the last treatment (D8). Data were analyzed using linear mixed models with Benjamini-Hochberg adjustments. RESULTS: Lung resistance significantly improved at D4 (mean decrease ± SD, -1.5 ± 0.45 cm H₂O/L/s; 95% confidence interval [CI], -2; -0.6) and D8 (-1.4 ± 0.45 cm H₂O/L/s; 95% CI, -2.4; -0.5) compared to baseline in the OR group only (P = .004 and .01, respectively). Serum cortisol concentration was significantly decreased at D4 and D8 for both groups (maximum decrease, -1.2 ± 0.3 μg/dL; 95% CI, -1.9; -0.6 at D4 for NE group and -2.2 ± 0.3 μg/dL; 95% CI, -2.8; -1.6 at D8 for OR group; P < .001). CONCLUSIONS AND CLINICAL IMPORTANCE: Oral, but not nebulized dexamethasone is an effective therapy for horses with severe asthma and both treatment modalities inhibit the hypothalamic-pituitary-adrenal axis.