The primary signs of chronic bronchial disease include cough and wheeze, and these signs are frequently the result of some
degree of airway smooth muscle contraction. In clinical practice, it usually is difficult to distinguish between chronic bronchitis
and asthma in coughing cats. It is tempting to treat coughing cats with suspected bronchial disease by using only bronchodilators
to relax the airway smooth muscle contraction. Although this is a central method of treatment when acute signs develop, it
is critically important to understand that asthmatic and bronchitic airways show evidence of chronic ongoing inflammation
whether the cat is symptomatic or not. Therefore, treatment strategies are most successful if they are directed toward decreasing
the underlying inflammatory component of the disease in addition to addressing the acute clinical signs of cough, wheeze and
increased respiratory effort.
The most effective long-term treatment of chronic non-infectious bronchial disease is systemically administered corticosteroids.
This class of drugs is most likely to suppress airway inflammation, a process orchestrated by a network of proteins (cytokines)
that act on circulating and structural airway cells. An important effect of steroids is to inhibit the synthesis of genes
for cytokines that are important in generating airway inflammation.
The side effects of systemic steroid medications given for long periods are undesirable. Fortunately, inhaled steroids have
become available that do not cause systemic side effects, and this therapeutic approach has greatly enhanced our ability to
treat cats with bronchial disease.
Treatment of bronchitic or asthmatic cats begins with signs that occur more than once weekly (without medication) and includes
prednisolone, 1 to 2 mg/kg orally every 12 hours for five to seven days.
At this point, the majority of newly diagnosed cats have greatly diminished signs. The dose of steroids is then tapered slowly,
over at least two to three months. This approach is much more effective than giving low doses of prednisone for short periods
and in response to acute flare-ups.
Cats with signs that occur less than once weekly (without medication) generally are not considered to have chronic active
inflammatory airways. These cats may be safely treated with bronchodilators when needed.
Some cats are effectively and safely managed by administration of low-dose, alternative-day corticosteroids. However, most
cats with chronic bronchial disease continue to wheeze/cough when treated in this conservative manner. For cats with a good
response to higher doses of consistently administered systemic corticosteroids, inhaled corticosteroid therapy should be encouraged
as an alternative to reduce adverse effects.
The most commonly used inhaled corticosteroid is fluticasone propionate, a synthetic corticosteroid with an 18-fold higher
affinity for the corticosteroid receptor when compared to dexamethasone. Binding of the steroid to this receptor results in
a new molecular complex that leads to up or down regulation of the gene and its products. Fluticasone, like other corticosteroids,
acts to inhibit mast cells, eosinophils, lymphocytes, neutrophils and macrophages involved in the generation and exacerbation
of allergic airway inflammation by transcriptional regulation of these target genes. Preformed and newly secreted mediators
including histamine, eicosanoids, leukotrienes and multiple cytokines are inhibited as well.
Fluticasone is a large molecule and acts topically within the airway mucosa. Because there is delayed absorption across mucosal
epithelium, there is minimal oral systemic bioavailability. Plasma levels do not predict therapeutic effects. This explains
the lack of systemic side effects. Optimal clinical effects, therefore, may not occur for one to two weeks.
The drug usually comes in three strengths: 44 mcg, 110 mcg and 220 mcg per actuation. The 44-mcg dosing twice daily does not
consistently result in acceptable clinical responses. For cats with mild to moderate disease, 110 mcg given twice daily frequently
results in clinical responses equivalent to that achieved by administration of 5 mg oral doses of prednisone given BID. Cats
with more serious disease may require 220 mcg inhaled BID. Administration of fluticasone more than twice daily has not resulted
in clinical benefit.