Efficacy of oral prednisolone and dexamethasone in horses with recurrent airway obstruction in the presence of continuous antigen exposure

P>Reasons for performing study: Orally administered prednisolone and dexamethasone are used commonly in the treatment of recurrent airway obstruction (RAO) in horses. However, the efficacy of prednisolone in improving pulmonary function during continuous antigen exposure has not been evaluated critically and there is little evidence supporting the efficacy of low-dose oral dexamethasone in the same conditions. Hypothesis: Oral prednisolone and dexamethasone improve pulmonary function in RAO under conditions of continuous antigen exposure, and dexamethasone is more effective than prednisolone at commonly used dosages. Methods: Using a randomised crossover design, prednisolone (2 mg/kg bwt) and dexamethasone (0.05 mg/kg bwt) were administered per os, s.i.d. for 7 days, to 7 horses during clinical exacerbation of the disease. Maximal difference in transpulmonary pressure (Delta P-L), lung resistance (R-L) and elastance (E-L) were measured before and after 3 and 7 days of treatment. Results: Prednisolone and dexamethasone improved pulmonary function significantly. However, the improvement was of greater magnitude after 3 and 7 days of treatment with dexamethasone compared to prednisolone. Also, after 7 days of treatment with dexamethasone, Delta P-L and R-L were not different from values obtained when horses were on pasture, while all 3 pulmonary function parameters remained different from pasture values after prednisolone treatment. Conclusions: Both corticosteroids improve pulmonary function, in spite of continuous antigen exposure. However, oral dexamethasone at 0.05 mg/kg bwt is more effective than prednisolone at 2 mg/kg bwt in the treatment of RAO. Potential relevance: Prednisolone was shown, for the first time, to our knowledge, to improve the pulmonary function of horses with RAO in the presence of continuous antigen exposure. This study also demonstrates the efficacy of low-dose oral dexamethasone in reversing airway obstruction in these conditions.