Residual contamination in nebulization medication cups after corticosteroid administration: an in vitro assessment with implications for equine doping control.

BACKGROUND: Nebulization is increasingly used to administer respiratory medications in horses. However, the potential for residual contamination in medication cups after administering regulated substances raises concerns about inadvertent doping. OBJECTIVES: To evaluate whether medication cups used for nebulization of corticosteroids can subsequently be used for administration of non-regulated substances without detectable carryover. STUDY DESIGN: In vitro experimental study. METHODS: Three corticosteroids (budesonide, dexamethasone, fluticasone propionate) were nebulized using Flexineb™ medication cups. Following drug nebulization, saline was nebulized through the same cup both before and after the manufacturer's recommended cleaning procedure. Each experiment was performed in triplicate using independent medication cups. Samples were collected from the initial drug formulations and from the nebulized drug and impacted saline fluid collected before and after cleaning. Drug concentrations were quantified using validated analytical methods. RESULTS: Corticosteroids were detected in all saline samples nebulized after corticosteroid administration, both before and after cleaning. Cleaning reduced mean residual corticosteroid concentrations in impacted saline fluid by >99.9% for budesonide, 95.5% for dexamethasone, and 91.4% for fluticasone propionate. All post-cleaning samples remained detectable, above the limit of quantification. MAIN LIMITATIONS: In vitro study with no assessment of inhaled dose, systemic absorption, or biological matrices; recovered volume not measured; limited number of formulations, cleaning protocols, and medication cup materials. CONCLUSIONS: Routine cleaning markedly reduced but did not eliminate corticosteroid carryover from medication cups. The interchangeable use of medication cups after corticosteroid nebulization may pose a contamination risk. The use of separate cups for corticosteroids and non-regulated substances should be considered.