Do Bronchodilators Help Horses With Equine Asthma?
In horses with equine asthma, veterinarians often recommend administering bronchodilators to relieve constriction of the bronchi (the airways into the lungs) caused by muscle contraction or spasm. Such medications include inhaled long-acting bronchodilators such as antimuscarinic agents and b2-adrenoceptor agonists (e.g., albuterol).

Despite the widespread recommendation and use of these medications, one group of Italian researchers recently highlighted the dearth of data showing that bronchodilators improve lung function to ameliorate clinical signs of asthma.

“Robust evidence demonstrates that bronchodilators significantly improve the respiratory mechanics in horses with severe asthma,” said Luigino Calzetta, PhD, from the Unit of Respiratory Medicine in the University of Rome Tor Vergata’s Department of Experimental Medicine. “But whether or not simply improving the airway obstruction actually improves lung function and helps horses ‘breathe easier’ remains unclear.”

To more comprehensively determine bronchodilators’ role in treating equine asthma, Calzetta and colleagues retrospectively reviewed and extracted data from previously published research. In total they identified 33 asthmatic horses in five studies published between 2000 and 2008.

In their study, Calzetta and his team assessed various measures of lung function, including pulmonary resistance—the ratio of driving pressure to the rate of air flow, as measured using a forced oscillation technique or a pneumotachograph. They combined these variables with clinical scoring systems to assess horses’ clinical improvement (e.g., less coughing, normal respiratory rate and effort) following treatment with bronchodilators.

The team aimed to use pulmonary resistance and the clinical scoring system to identify the “minimal important” difference in lung function that leads to a “meaningful improvement in clinical signs.”

Based on their analyses, bronchodilators can result in an improvement of ≥1 cm H2O/liter/second in pulmonary resistance—a change that increases lung function enough to result in significant improvement in clinical signs.

Calzetta said this means bronchodilators can, indeed, improve lung function rather than simply dilating constricted bronchioles.

The study, “Clinical efficacy of bronchodilators in equine asthma: Looking for minimal important difference,” will be published in an upcoming edition of Equine Veterinary Journal. The abstract is available on PubMed.