Choosing Corticosteroids for RAO: Systemic or Inhaled?

Inhaled corticosteroids appear more appropriate to use on horses with mild RAO than those with severe disease because they take longer to provide relief.

Photo: Mathilde Leclere, DVM, PhD, Dipl. ACVIM

While there's no definitive cure for recurrent airway obstruction (RAO, commonly known as heaves), veterinarians are well-versed in managing the condition. Many will add a corticosteroid—either systemic or inhaled—to an affected horse's therapeutic regimen, but which type is the better choice?

Imogen Johns, BVSc, Dipl. ACVIM, MRCVS, a senior lecturer in equine medicine at the Royal Veterinary College, in Hertfordshire, U.K., sought to answer that question at the 2014 British Equine Veterinary Association Congress, held Sept. 10-13 in Birmingham, U.K.

Recurrent airway obstruction is an inflammatory lower airway disease similar to asthma in humans. Affected horses' airways are so obstructed by inflammation, mucus, and bronchial muscle contraction (bronchospasm) that the animal has difficulty breathing—even at rest. The condition is often caused by inhaled particles or irritants that end up in the horse's lungs, triggering airway inflammation.

Johns said RAO therapy is multifaceted and should involve:

  • Minimizing the horse's allergen exposure (keeping the horse in a low-allergen or allergen-free setting and providing low-dust or -allergen feeds, among other steps);
  • Treating bronchospasm (with a bronchodilator, such as clenbuterol); and  
  • Treating airway inflammation.

Veterinarians can choose between treating the airway inflammation systemically with an oral or injectable corticosteroid or locally with an inhaled product. Systemic options include dexamethasone (which can be administered orally, intravenously, or intramuscularly), prednisolone (administered orally), and triamcinolone (administered intramuscularly).

Inhaled options include beclomethasone and fluticasone, Johns said, and three different inhalers: the Equihaler, the Aerohippus, and the Aeromask (which, she said, is no longer commercially available). She also noted that the amount of medication the horse receives with each use varies by device, and the inhalers' propellant changes between drugs, which can alter the drug's deposition in the horse's lungs.

So which is better—systemic or inhaled corticosteroids? It seems to depend on the horse and the severity of his condition.

Johns reviewed published research on the topic with the veterinary attendees, drawing conclusions from each study she presented. Ultimately, based on the research, she concluded that:

  • There is less "good" evidence supporting the use of inhaled versus systemic corticosteroids;
  • Systemic corticosteroids—specifically dexamethasone—appear most appropriate for horses with severe disease because they elicit the quickest improvement; and
  • Inhaled corticosteroids are more appropriate to use on horses with mild disease because they appear to take longer to provide the horse relief.

Johns cautioned that none of the studies she described evaluated the corticosteroids' effects when coupled with a bronchodilator—as is commonly done in practice—and stressed that minimizing the horse's allergen exposure is a crucial management practice to ensuring the best outcome.

Still, she said, veterinarians should feel comfortable applying this information to horses in their practices.

About the Author

Erica Larson, News Editor

Erica Larson, news editor, holds a degree in journalism with an external specialty in equine science from Michigan State University in East Lansing. A Massachusetts native, she grew up in the saddle and has dabbled in a variety of disciplines including foxhunting, saddle seat, and mounted games. Currently, Erica competes in eventing with her OTTB, Dorado.

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