What are the first-line and adjunct therapies for equine asthma and recurrent airway obstruction?

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Environmental modification is the cornerstone of equine asthma management and must accompany all pharmacologic therapy — corticosteroids and bronchodilators alone are insufficient without reduction or elimination of triggering airborne antigens. 458 Clinical signs resolve within 3–4 weeks of appropriate environmental changes alone. 5 For acute exacerbation with labored breathing at rest, rescue bronchodilation is the immediate first priority. Inhaled albuterol (salbutamol) produces a 61.1% decrease in transpulmonary pressure and has a duration of action of 60 minutes. 12 Inhaled levalbuterol achieves an equivalent magnitude of bronchodilation (59.9% decrease in transpulmonary pressure) with a duration of action of 120 minutes, but this remains too short for use as a maintenance bronchodilator; both agents are therefore limited to rescue or diagnostic use. 12 Corticosteroids are the most effective anti-inflammatory drugs for severe equine asthma. Among systemic agents, dexamethasone is the most potent in comparative studies; triamcinolone, isoflupredone, and prednisolone are also efficacious. 1 Systemic corticosteroids are associated with adrenal suppression, decreased immune function, and possible laminitis with prolonged use, and clinical signs relapse soon after cessation in the absence of environmental intervention. 1 For this reason, systemic corticosteroids are typically administered for days to weeks only. 1 Inhaled corticosteroids are the preferred long-term anti-inflammatory strategy, providing equivalent efficacy to systemic dexamethasone at appropriate doses with a more favorable safety profile. Inhaled fluticasone and beclomethasone at appropriate doses produce equivalent effects on severe equine asthma as intravenous dexamethasone, though inhaled corticosteroids take longer to achieve the desired effect. 10 Inhaled budesonide, delivered via a Respimat-based equine device, improves lung function to a similar magnitude as systemic dexamethasone at higher d