Nebulisation of dexamethasone sodium phosphate for the treatment of severe asthmatic horses

Inhaled corticosteroids are effective in the treatment of equine asthma. A recent study reported that nebulisation of injectable dexamethasone had low systemic bioavailability in healthy horses and could represent a cost-effective therapy for equine inflammatory lung diseases.

To determine the effects of dexamethasone nebulisation on lung function in severe asthmatic horses. It was hypothesised that dexamethasone administered by nebulisation would be more effective than the same dose administered orally.

Randomised blinded experimental study in severe asthmatic horses.

Twelve severe asthmatic horses in clinical exacerbation were randomly assigned to treatment with 5 mg of dexamethasone sodium phosphate by nebulisation (n = 6) or by oral administration (n = 6), once daily for 7 days. Lung function was evaluated at baseline, after four treatment days (D4) and 24 h after the last dose (D8). The presence of residual bronchospasm was assessed on D8 with N-butylscopolammonium bromide administration (0.3 mg/kg i.v.). A respiratory clinical score was performed daily. Serum cortisol concentration was measured at baseline, D4 and D8.

The pulmonary elastance was unchanged in both groups while pulmonary resistance was significantly improved in the oral group on D8 (mean reduction in 1 cm H₂ O/L/s [CI: 0.34-1.65, P = 0.003]). All horses had residual bronchospasm at the end of the study. There was a group difference in the respiratory clinical score as it was significantly reduced in the oral group, from D5 to D8. Serum cortisol concentration decreased in all subjects.

Low number of horses and lack of placebo group.

Considering the lack of improvement of lung function and the hypothalamic-pituitary-adrenal axis suppression, the results of this study do not support aerosolisation of an injectable form of dexamethasone for the treatment of severe equine asthma at the dose and with the nebuliser evaluated.