Respiratory Disease - Inhalant Therapy

Photo of a horse wearing the Aeromask. A clinician is administering the aerosolized mediation via a spray.
Photo of a horse wearing the Aeromask. A clinician is administering the aerosolized mediation via a spray.

Chronic Obstructive Pulmonary Disease (COPD or "heaves") is a progressive inflammatory disease of the lower airways. It results from chronic inhalation of airborne dusts and molds commonly associated with hay and bedding. COPD is debilitating and widespread; studies have indicated that lower airway diseases like it are common causes for poor performance in athletic horses. The silver lining to this grim statistic is the advent of devices that allow medications to be administered via the inhalation route as opposed to the traditional oral and injectable methods. This is beneficial for a number of reasons, and the use of metered-dose inhalers (MDI) is quickly becoming the cornerstone of many effective treatment protocols.

Management of the horse’s environment is one of the most effective therapies for COPD, but the methods for improving the horse’s "breathable environment" (i.e. pasturing rather than stabling them and feeding pelleted diets rather than hay) often are not compatible with harsh Vermont winters and the slowing economy. Horses handle cold weather just fine, but we do not; most horse owners do not feel comfortable leaving their companions outside and exposed when the temperatures reach the freezing mark. Additionally, most pelleted feeds are more expensive than an equivalent amount of hay. Because of these practical limitations, medications often bear the burden of successful COPD treatment.

Corticosteroid and bronchodilator medications have long been recommended for the effective treatment of COPD. When used simultaneously, these drugs do an excellent job of reducing airway inflammation, decreasing mucus production, and counteracting small airway constriction. This triad of inflammation, mucus, and constriction is what leads to the signs of exercise intolerance, nasal discharge, cough, and respiratory distress in affected horses. Despite the benefits of these medications, administering them orally or via an injectable route can be limiting. They are often not absorbed well through the GI tract and therefore reach sub-optimal concentrations where it really matters – the lungs. More importantly, the long- term use of steroids can be associated with harmful systemic side effects even when the dose is tapered over time.

Delivery of these same medications through a MDI system is advantageous for a number of reasons. Corticosteroids lend themselves especially well to administration via an inhaled route. As is the case with many medications, corticosteroids must attach to receptor sites located on the surfaces of various internal body tissues in order to have a therapeutic effect. There are large numbers of these receptors located within the lungs. This means that the drug’s effect is much more potent when inhaled as compared to that which is obtained when it is injected or swallowed. Furthermore, inhaled medication rarely reaches threatening levels in the horse’s bloodstream with routine use. Subsequently, the chance for potentially harmful side effects is greatly reduced. This liberal safety margin makes possible the use of a wider variety of more potent medications as compared to those that are available for Injectable or oral use. Bronchodilators that are administered through a metered-dose inhaler similarly reach higher concentrations in the lower airways than they do when given orally. Additionally, in the case of some bronchodilator medications, a dramatic improvement in airway diameter can be noted within several minutes after successive puffs are administered. This is especially helpful in the instance where a horse is experiencing respiratory distress (similar to a human asthma attack) since administration of the same medication via an oral route may take several hours or days to have the same effect.

A practical benefit of inhalant therapy in horses is that it’s a procedure that owners can easily learn and perform themselves; the time commitment is negligible, and since most medications are available at human pharmacies, prescription refills are fast and convenient. The Equine Aeromask (Canadian Monaghan, London, Ontario, Canada) is the most widely used device used for delivery of inhaled medications. It has been available for several years and most horses tolerate it well. The device is a plastic mask that fits snugly over both nostrils and is held in place by an adjustable nylon strap that runs over the poll. There is a port at the "nose end" of the apparatus, into which an inhaler is inserted. The owner then administers two to six puffs of each medication as the horse inspires. The entire procedure only takes several minutes and is typically done twice daily. Manufacturers are in the process of improving the design of this device and a less cumbersome inhaler that is hand-held over only one nostril will soon be widely available. Studies have shown that this device may be capable of delivering up to a five times greater concentration of drug as compared to the Aeromask.

The concept of equine inhalant therapy for lower airway disease is now coming into its own. The medications that are available and the means by which we administer them mirror that of human medicine. Just as inhalers have become life saving devices for people with asthma, we are now able to greatly improve the quality of our horses’ lives in an increasingly safe and effective manner. If environmental management is limited or not adequate to achieve the desired effect alone, the use of inhalant therapy can be essential in helping your companion live a long, happy, productive life.

Administering aerosolized medication with one nostril inhaler.
Administering aerosolized medication with one nostril inhaler.

In the picture on the right a newer product is being used to administer the inhaled medication. The horses are usually more accepting of this one nostril administrator versus the aeromask pictured above. As you can see the horse's head can be held and the inhalant sprayed by the same person.

The concept of equine inhalant therapy for lower airway disease is now coming into its own. The medications that are available and the means by which we administer them mirror that of human medicine. Just as inhalers have become life saving devices for people with asthma, we are now able to greatly improve the quality of our horses’ lives in an increasingly safe and effective manner. If environmental management is limited or not adequate to achieve the desired effect alone, the use of inhalant therapy can be essential in helping your companion live a long, happy, productive life.

see article on Respiratory Disease - Exercise Intolerance.