Bronchodilators are frequently used to attenuate
airway obstruction in equine heaves (or recurrent
airway obstruction). This study evaluated the selective (M(3) and M(1))
muscarinic antagonist revatropate, which offers potential advantages over non-specific
antimuscarinic agents such as
ipratropium. Protocol 1 assessed the response to inhaled
revatropate (1, 2 and 7 mg) using a blinded, negative (inhaled saline) and positive (inhaled
ipratropium bromide; 0.3, 0.7 and 2mg) controlled, dose escalation study, with six heaves horses. The lowest doses of
revatropate and
ipratropium induced a rapid (within 1h) and significant improvement in airway function. The highest doses of both drugs had no significant effect on gastrointestinal sound score or iris function, but resulted in tacky mucous membranes and reduced gastrointestinal sound score in some horses. In Protocol 2, a cross-over design comparing the duration of action of inhaled
revatropate (1mg),
ipratropium (0.3mg) and saline, some indices of airway function were improved for between 5 and 6h after
revatropate administration, and for between 6 and 24h after
ipratropium administration. Inhaled
revatropate and
ipratropium had similar effects on airway function, with no significant difference between their efficacies. Importantly, however, only
revatropate significantly improved clinical scores of breathing effort, improving combined clinical score at the 1h time point and abdominal score at the 1-3h time points. No significant adverse events were observed in Protocol 2, although some horses had reduced gastrointestinal sound scores. Inhaled
revatropate is therefore a safe and effective
bronchodilator for treating
airway obstruction in heaves.