Pulmonary function and adrenal gland suppression with incremental doses of aerosolized beclomethasone dipropionate in horses with recurrent airway obstruction

Objective - To evaluate clinical response, pulmonary function, and adrenal gland response to incremental doses of beclomethasone dipropionate in horses with recurrent airway obstruction. Design - Crossover trial. Animals - 8 horses with recurrent airway obstruction. Procedure - Horses randomly assigned to 4 groups were treated twice daily via aerosol administration of placebo or 500, 1,000, or 1,500 μg of beclomethasone dipropionate in a crossover design with a 10-day minimum washout period. Subjective assessment of airway obstruction, serum cortisol concentration, and maximum change in pleural pressure during tidal breathing (ΔPpl(max)) were determined daily prior to morning drug administration, and ΔPpl(max) was reevaluated 15 minutes after morning drug administration. Pulmonary resistance and dynamic compliance were determined at baseline and approximately 12 hours after the final treatment. Results - An immediate treatment effect was not identified. Within 24 hours, ΔPpl(max) and airway obstruction were lower in horses receiving beclomethasone. Onset and magnitude of response was similar among the 3 beclomethasone dose regimens. Pulmonary resistance was improved only after administration of all 3 doses of beclomethasone, whereas dynamic compliance was improved after administration of 1,000 μg and 1,500 μg of beclomethasone. Reduction in serum cortisol concentration occurred with all 3 beclomethasone dose regimens; however, the magnitude of adrenal gland suppression was greater in horses receiving 1,000 or 1,500 μg of beclomethasone. Conclusions and Clinical Relevance - Low-dose (500 μg) beclomethasone administration caused similar improvement in pulmonary function, compared with high-dose beclomethasone (1,000 and 1,500 μg), with the exception of dynamic compliance, and caused less suppression of endogenous cortisol production.