“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