Metered dose inhalers now popular in treating feline asthma
Feline asthma is defined as a chronic inflammatory disease of the lower airways that results in cough, wheeze and exercise intolerance.
Feline asthma appears to be clinically similar to human asthma. In humans, treatment with inhaled medications administered via metered dose inhalers is routine. These metered dose inhalers (MDIs) are often used in combination with a device referred to as a "spacer" which allows medication to be dispersed into a chamber before inhalation. Spacers used in combination with small masks make it possible to administer inhaled medications to infants and very small children.
The use of MDIs in combination with spacers and face masks is now gaining popularity in the treatment of feline asthma.
The diagnosis of feline asthma should be based on the presence of several criteria including a history of chronic cough or history of sudden onset of labored breathing that improves with administration of oxygen, bronchodilators and/or glucocorticoids; radiographic findings consistent with bronchial wall thickening; and airway cytology characterized by a predominance of eosinophils and absence of evidence of infection and parasitism.
In a recent article in Veterinary Clinics of North America, Dr. Philip Padrid has suggested a classification scheme for cats diagnosed with feline asthma (Padrid, P. Feline Asthma: Diagnosis and Treatment. In Vet Clin North Am Small Anim Pract 30: 1279 1293, 2000). This scheme may be used to guide medical therapy:
· Mild asthma. Signs are mild and do not affect the cat's quality of life. Appetite and activity is normal between episodes.
· Moderate asthma. Signs are intermittent but frequency or duration of signs are such that the patient's quality of life (appetite, activity and/or sleep) is affected.
· Severe asthma. Signs are persistent and evident even at rest.
It has been established in humans that asthma is characterized by chronic inflammation of the airways even in the absence of clinical signs.
For this reason, bronchodilators are seldom used as the sole therapy for human asthma. While bronchodilators may control clinical signs, airway inflammation persists and there is the potential for this chronic inflammation to result in irreversible airway damage. A research abstract presented at the 2001 ACVIM Forum (Norris, CR. Cytokine profiles in peripheral blood mononuclear cells and bronchoalveolar lavage cells in cats with experimental feline asthma) documented the increase in inflammatory mediators associated with experimental allergic airway disease in the cat.
As in human asthma, it would therefore seem important that treatment not only control the clinical signs but also minimize airway inflammation.
In the past, oral corticosteroids and bronchodilators have been the recommended therapy for feline asthma but, while oral medication can accomplish the desired therapeutic goals, there can be unwanted systemic side effects.
In humans, systemic side effects are minimized and therapeutic efficacy maximized by using inhaled medications. Padrid has suggested that these inhaled medications can also be efficaciously delivered to feline patients.
In his article, Padrid suggests using a spacer device with a small animal anesthesia mask attached to the end.
In my practice, I have had good results using a small OptiChamber face mask with the Optichamber spacer. I recommend that the client acclimate their cat to the apparatus before they begin to administer medication by attaching the mask to the chamber and placing the mask over the pet's face for short periods of time. Once the pet can tolerate the face mask for seven to 10 breaths, medication can be administered through the chamber.
In order not to startle the cat, I recommend that the inhaler and Optichamber, apparatus be held away from the patient and the inhaler depressed to release medication into the chamber. The face mask should be immediately positioned over the cat's nose and the cat allowed to take seven to 10 breaths.
According to Padrid, therapy for asthma in the cat should be based on the previously described classification scheme. If the patient's clinical signs are mild, two puffs of Fluticasone propionate (Flovent,) 110 µg twice daily are recommended. Albuterol 90 mg (Ventolin, Proventil) may be used as needed but will not likely be required long-term. If the patient's clinical signs are moderate, oral prednisone at a dose of 1 mg/kg twice daily for five days and then daily for five days should be prescribed along with 220 µg Flovent, twice daily. Again, Albuterol should be used as needed.
If the patient's clinical signs are severe, treatment should initially include a parenteral glucocorticoid such as dexamethasone combined with Albuterol 90 mg administered every 30 minutes until the clinical signs abate or a total of eight doses is reached. Once stable, medical therapy should be the same as for those patients with moderate signs with the exception of administering Albuterol four times daily or as needed.
The use of inhaled medications appears to be a reasonable approach to the treatment of feline asthma.
It can be inferred from what is known about asthma in humans that this approach minimizes systemic side effects while achieving desired therapeutic results.
Unfortunately, studies that look critically at the effects of inhaled medication in the cat are lacking. However, in my experience and the experience of others using these medications, clinical response is often good.