AAEP Convention 2005: Chronic Salbutamol Treatment for Inflammatory Airway Disease

"Anywhere between 25-92% of stabled horses have some form of airway inflammation," said Melissa R. Mazan, DVM, of Tufts University's Cummings School of Veterinary Medicine, at the 2005 American Association of Equine Practitioners Convention in Seattle, Wash. "The overarching goal of treatment is to improve or maintain quality of life and athletic potential."

For that reason, Mazan and her colleagues recently examined chronic use of inhaled salbutamol (generic name albuterol), a frequently used drug for inflammatory airway disease (IAD), and found that it was helpful to horses. They also showed that, at least over the study time of 10 days, the horses did not develop a tolerance to the drug as a former study had suggested.

Mazan examined seven athletic horses with moderate airway hyper-responsiveness to histamine (researchers could induce airway reactivity reliably) and their reactions to 10 days of aerosolized salbutamol, a beta-2 adrenergic (B2-AR) agonist, given twice daily. B2-ARs exert their effects on smooth muscle by binding to and stimulating a cellular receptor called the beta-2 receptor. The beta-2 receptor, when bound and activated, relaxes the smooth muscles in the airways, causing them to dilate.

A 2001 study on horses with heaves showed that twice-daily chronic albuterol use led to tolerance of the bronchodilator effects of the drug. Therefore, Mazan and others thought that chronic use of B2-ARs would desensitize  horses with the milder disease, IAD, and salbutamol would become ineffective as a rescue drug if the horse were to have a bronchoconstrictive event.

To measure airway response, Mazan used a non-invasive open plethysmography system developed at Tufts by Andy Hoffman, DVM, DVSc, Dipl. ACVIM. This system involves the horse wearing bands at the rib and at the abdomen to measure the movement of each area as the horse breathes. This allows researchers to quantify and compare the amounts of air the horse inhales, that which reaches the lungs, and the expiratory airflow at the nostril. "When an animal has bronchoconstriction, there is a blocked movement of air," she explained. "There's too much resistance to the flow (of air). When the horse breathes out, there is a larger change at the rib cage than at the nose."

The researchers were surprised to find that salbutamol maintained its bronchoprotective effect--the horses weren't desensitized to the drug. "This may be because of the high turnover of B2-ARs on smooth airway muscle, or it may also reflect a strong innate bronchoprotective effect in the airways of the horse," Mazan said. In asthmatic humans, B2-ARs work very well over time, but can fail during acute severe asthma attacks, so Mazan said it's important to avoid extrapolating data from horses with moderate IAD (such as the horses in the current study) to horses with severe heaves.

About the Author

Stephanie L. Church, Editor-in-Chief

Stephanie L. Church, Editor-in-Chief, received a B.A. in Journalism and Equestrian Studies from Averett College in Danville, Virginia. A Pony Club and 4-H graduate, her background is in eventing, and she is schooling her recently retired Thoroughbred racehorse, Happy, toward a career in that discipline. She also enjoys traveling, photography, cycling, and cooking in her free time.

Stay on top of the most recent Horse Health news with FREE weekly newsletters from TheHorse.com. Learn More

Free Newsletters

Sign up for the latest in:

From our partners