Endocrine and immunologic effects of inhaled fluticasone propionate in healthy dogs

Background: Inhaled glucocorticoids reduce airway inflammation while minimizing systemic effects in several species. Hypothesis: Inhaled fluticasone suppresses the hypothalamic-pituitary-adrenal axis (HPAA), modifies immune function, and induces clinical signs to a lesser extent than PO-administered prednisone in dogs. Animals: Seven healthy adult pet dogs. Methods: Dogs were randomized to 1 of 3 treatment groups in a crossover design: fluticasone propionate (220 mu g actuation of a metered dose inhaler delivered via a spacer and mask, q12h), placebo (spacer and mask alone, q12h), or prednisone (1 mg/kg PO q24h). Each treatment was administered for 3 weeks followed by a 4-week washout. Appetite, attitude, and water consumption were recorded during the last week of each treatment period. Urine cortisol : creatinine ratios, ACTH stimulation tests, white blood cell counts, lymphocyte phenotype, and serum IgM and IgA concentrations were recorded at each baseline and after the last day of each treatment. Clinical observations were expressed descriptively. Friedman's test was applied to all data comparisons. Pairwise comparisons were made with a mixed model analysis when data were normally distributed, whereas signed rank tests were used otherwise (significance P-value <.01). Results: Appetite and water consumption increased during prednisone treatment. Peak serum cortisol concentrations post-ACTH were significantly decreased in prednisone- and fluticasone-treated dogs compared with placebo (prednisone > fluticasone). Serum IgM concentrations were significantly decreased in dogs treated with prednisone. Conclusions and Clinical Importance: As used, fluticasone suppresses the HPAA to a lesser extent than prednisone and may avert systemic signs associated with PO-administered glucocorticoids in dogs.