Assistant Professor, Equine Internal Medicine Texas A&M University College of Veterinary Medicine & Biomedical Sciences College Station, Texas, United States
Background: Compounded fluticasone suspensions are routinely nebulized in horses to manage equine asthma because of limitations with inhaler formulations. Clinical recommendations often promote empirical dilution and nebulizer selection to enhance delivery. However, dilution can fundamentally alter particle size distribution (PSD), nebulizer efficiency, and pulmonary drug deposition. Suspensions can also behave unpredictably in nebulizers. To date, compounded fluticasone has not been systematically evaluated across equine nebulizers, and the effects of dilution remain undefined. Hypothesis/
Objectives: To characterize aerosol PSD, flow rate, and bulk aerosol output of fluticasone suspension nebulized undiluted or diluted 1:1 with saline. Animals:No animals used. Methods: Compounded fluticasone propionate suspension (1 mg/mL) was nebulized at stock concentration and after 1:1 dilution with 0.9% NaCl using six equine nebulizers (three jet, three vibrating mesh); each condition was tested in triplicate. Aerosol PSD was measured by laser diffraction using a closed inhalation cell. Flow rate was determined gravimetrically. Each condition was tested in triplicate. Effects of device, dilution, and device–drug interactions were analyzed using linear mixed effects models (p < 0.05). Results: PSD parameters, flow rate, and bulk aerosol output differed significantly among nebulizers and between concentrations (p < 0.01). Dilution increased flow rate relative to undiluted suspensions (p < 0.01) but produced larger median particle sizes (p < 0.001). Conclusions and Clinical Importance: Nebulizer selection and empirical dilution substantially influence aerosol characteristics of compounded fluticasone. These findings challenge assumptions of device interchangeability and support development of evidence-based nebulization protocols for horses.
