Diplomate American College of Veterinary Internal Medicine
Nashville Veterinary Specialists – Clarksville
In small animal practice, we treat patients with chronic airway disease on a daily basis. In the dog, this includes chronic bronchitis, chronic rhinitis, pulmonary infiltrates with eosinophils, collapsing trachea, and chronic obstructive pulmonary disease (often the end- stage of chronic bronchitis). In the cat, we most commonly treat asthma, bronchitis, and chronic rhinitis. Common features of all of these conditions are inflammatory cell infiltrates and increased airway secretions, with varying degrees of eosinophilia, bronchial constriction, structural alterations and secondary bacterial infections. These diseases require life-long management with the goal of controlling clinical signs and slowing disease progression.
A large handful of systemic medications are available to treat these diseases, but are associated with differing degrees of side effects. Systemic corticosteroids are typically quite effective in controlling inflammation, and thus the clinical signs in most of these conditions. Unfortunately, corticosteroids are also associated with polydipsia, polyuria, polyphagia, weight gain (which exacerbates respiratory conditions), ligamentous weakness, muscular weakness, muscle mass loss, and ironically, notable alterations in breathing patterns in many dogs. In cats, insulin resistance and drug-induced diabetes mellitus is a risk of systemic corticosteroids. Systemic bronchodilators are problematic for the side effects of tachycardia, hypertension, and excitability. When these same classes of drugs are used locally, (i.e. when they are inhaled), there are minimal to no systemic side effects, and therapy is delivered directly to the site where it is needed the most. This presentation will review the most common inhaled medications and how to use these tools for long term therapy.
Inhaled corticosteroids are indicated any time chronic corticosteroid therapy is needed for airway disease, from nose to alveolus. This is especially true if the pet is known to be sensitive to systemic steroids, has diabetes mellitus, Cushing’s disease, pancreatitis, or for use in patients on other systemic immune suppressive therapy such as chemotherapy. Inhaled bronchodilators are useful in patients that are hypertensive or that become excitable on oral bronchodilators.
Inhaled medications are NOT expected to be helpful in the early stages of disease, because airway obstruction with mucus is common initially, and an inhaled medication cannot penetrate past that mucus. Inhaled medications are also not accepted by all pets. For example, brachycephalic breeds may be difficult to fit to a face mask, and some animals panic when the mask is placed across their muzzle. Therefore, control is typically achieved with oral medications, and control is maintained with inhaled medications where possible. Typically, there is a 2-4 week period of weaning off of oral medications while the inhaled medication begun (typically corticosteroids).
Inhaled medications can be administered via nebulization, or via a metered-dose inhaler. Nebulization allows administration of tiny droplets of medication that penetrate as far as the alveoli. A wide range of medications can be nebulized, including antibiotics (most often aminoglycosides), corticosteroids, bronchodilators, mucolytics, and often just saline. The disadvantage of nebulization is primarily the time it takes to give the medication and the dispersal of excess medication into the surrounding air (which is then inhaled by the caretaker). Nebulization usually takes 5-10 minutes. One way to make nebulization easier is to place the patient in a small carrier that has approx. 80 % of the openings covered by plastic wrap, with the nebulizer placed in front of the patient’s face.
Metered-dose inhalers are a more precise way to administer inhaled medications. The design of these inhalers has changed in recent years, such that the propellant changed from chlorofluorocarbon to hydrofluorocoarbon, or more commonly breath-actuated inhalers. The newer “discus” and turbohaler styles are not suitable for use in animals, as they typically deliver a powder, not a solution. The inhalers that are usually used for our patients are those that are used for pediatric or debilitated human patients.
Since we cannot ask our patients to properly use a metered dose inhaler (“puffer”), we must use an adapter, consisting of a hollow tube spacing chamber which holds the actuated dose of medication, and a face mask to deliver the dose to the pet. The mask must fit over the nostrils and the mouth, and the pet must inhale several times to receive the dose of medication. There are several companies that sell these devices, or even a pediatric administration set may be used on a small pet. The chamber/ mask apparatus from Aerodawg/ Aerokat (Trudell medical supply) has a one-way valve between the chamber and mask, which allows the pet owner to actually watch to be sure that the pet is inhaling the medicine.
The majority of pets can be taught to tolerate the inconvenience of receiving the inhaled medication with the help of the owner remaining calm and direct, and giving a treat afterwards. Reluctant cats can be bundled in a towel, and owners of reluctant dogs have to be reminded that most dogs are trainable. It is best in some cases to simply get the pet used to having something against the front of its face, such as an empty toilet paper tube, and reward the pet for remaining still when that is applied, then move on to the mask alone, and then the full apparatus next. We have helped elderly clients and owners of fractious cats learn the best way to give the medication. The websites also offer videos and written instructions (www.aerokat.com, www.aerodawg.com). Another very helpful support website is www.FritztheBrave.com; it has extensive links to support groups, tips on administration of medications, and useful suggestions.