Efficacy of oral and intravenous dexamethasone in horses with recurrent airway obstruction.
Authors: Cornelisse C J, Robinson N E, Berney C E A, Kobe C A, Boruta D T, Derksen F J
Journal: Equine veterinary journal
Summary
# Recurrent airway obstruction (RAO) is a common and costly condition in horses, yet clinicians have lacked clear guidance on dexamethasone dosing schedules and administration routes to optimise therapeutic outcomes. Cornelisse and colleagues conducted two carefully controlled crossover trials comparing intravenous and oral dexamethasone delivery in RAO-affected horses, measuring pulmonary function over extended periods to determine onset, peak effect and duration of action. Intravenous dexamethasone (0.1 mg/kg) produced significant improvement within 2 hours and peak effect by 4–6 hours, whilst oral administration at 0.164 mg/kg achieved effectiveness within 6 hours with maximal response at 24 hours—though this benefit was substantially reduced when horses were fed concurrently, indicating poor gastrointestinal absorption with food present. Both routes maintained statistically significant improvements for at least 30 hours compared to saline controls, with oral dosing tending toward longer duration despite slower onset. For practitioners, these findings indicate that oral dexamethasone solution administered to fasted horses offers comparable efficacy to intravenous treatment with potentially extended therapeutic windows, presenting a practical and cost-effective alternative for RAO management when rapid response is not required; however, careful attention to fasting protocols is essential to ensure adequate bioavailability and clinical benefit.
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Practical Takeaways
- •IV dexamethasone works rapidly (within 2 hours) for acute RAO cases; oral dosing to fasted horses provides equivalent long-term effect with potentially longer duration, offering a practical alternative for stable management
- •Always fast horses before administering oral dexamethasone solution—feeding reduces drug absorption by half, requiring dose adjustment and potentially compromising treatment efficacy
- •A single dexamethasone treatment provides therapeutic benefit for approximately 30 hours; plan dosing intervals and treatment protocols accordingly for RAO management
Key Findings
- •Intravenous dexamethasone (0.1 mg/kg) caused significant lung function improvement within 2 hours with peak effect at 4-6 hours in RAO-affected horses
- •Oral dexamethasone (0.164 mg/kg) given to fasted horses was effective within 6 hours with peak effect at 24 hours and comparable efficacy to IV administration
- •All dexamethasone treatments showed statistically significant duration of effect for 30 hours compared to saline, with oral administration tending toward longer duration
- •Fasting prior to oral dexamethasone administration improved bioavailability; feeding decreased bioavailability by approximately 50% (0.164 mg/kg fed ≈ 0.082 mg/kg fasted)