Nebulized Dexamethasone for Severe Equine Asthma: Yay or Nay?

The key to controlling equine asthma is allergen avoidance, though modern management practices can make this goal difficult. From time to time, owners of asthmatic horses must administer medications to bring relief to their horses. Veterinarians suggest that dexamethasone, an anti-inflammatory steroid, given as a nasal mist should benefit severely asthmatic horses, yet recent research yielded conflicting data.

Current treatment recommendations for asthma include dosing with dexamethasone or a similar anti-inflammatory steroid systemically, either orally, intramuscularly, or intravenously.

“Adverse effects associated with systemic administration of steroids include immunosuppression, laminitis, and dampening of the hypothalamic-pituitary adrenal axis, an influential neuroendocrine body system that controls a horse’s reaction to stress,” explained Kathleen Crandell, Ph.D., a nutritionist for Kentucky Equine Research.

Though standard treatments for asthma leave much to be desired in terms of efficacy, according to Crandell, alternate or adjunct therapies are constantly being trialed. One adjunct therapy recommended by veterinarians for asthmatic horses is nutritional supplementation with a high-quality source of omega-3 fatty acids, such as EO-3 from Kentucky Equine Research.

Administering steroids using a nebulizer serves as an alternate way to deliver medication. Nebulization turns a liquid medication into a fine mist, delivering the drug directly to the lungs during normal respiration. Nebulization may be a more efficient mode of drug delivery, potentially with fewer side effects than systemic administration. The method has been effective in humans with asthma.

For this study, researchers recruited 12 horses previously diagnosed with severe asthma. The horses were separated into two groups. Six were given 5 mg of dexamethasone with a commercially available nebulizer, and six received 5 mg of dexamethasone by oral administration. Lung function and serum cortisol, a measure of hypothalamic-pituitary adrenal axis function, were measured after a week of treatment.

Researchers found that, unlike oral dosing, nebulized dexamethasone proved an ineffective therapy for severe asthma. An undesirable suppression of the hypothalamic-pituitary adrenal axis was observed with both nebulized and oral treatments.

“The researchers suggested that higher doses or increased frequency might prove beneficial but, based on the available data, administering nebulized dexamethasone does not appear beneficial,” Crandell summarized.

Managing asthma in horses often requires a multipronged approach. In addition to any medications prescribed by a veterinarian for acute respiratory distress, everyday tactics for these horses may include soaking hay to reduce respirable particles, allowing ample time in turnout, and supplementing with a high-quality source of omega-3 fatty acids.

*de Wasseige, S., K. Picotte, and J. Lavoie. 2021. Nebulized dexamethasone sodium phosphate in the treatment of horses with severe asthma. Journal of Veterinary Internal Medicine 35(3):1604-1611.