Page 356 - Small Animal Internal Medicine, 6th Edition

328 PART II Respiratory System Disorders

require relatively high dosages of prednisone, have unaccept- may confer an additional benefit of mild antiinflammatory
able adverse effects, or have conditions for which glucocor- properties. The ability of doxycycline to reach therapeutic
VetBooks.ir ticoids are relatively contraindicated (e.g., diabetes mellitus) concentration within the airways is questionable because in
the dog it is highly protein bound, but the presence of inflam-
may benefit from local treatment with metered dose inhalers
(MDIs). This route of administration is discussed in greater
the drug. It is preferable to reserve fluoroquinolones for cases
detail later in this chapter, in the section on feline matory cells may increase locally available concentrations of
bronchitis. of serious infection.
Cough suppressants are used cautiously because cough is If an antibiotic is effective, a positive response is generally
an important mechanism for clearing airway secretions. In seen within 1 week. Treatment is then continued for at least
some dogs, however, the cough is incessant and exhausting, 1 week beyond the time when the clinical signs stabilize
or ineffective, because of marked tracheobronchomalacia. because complete resolution is unlikely in these animals.
Cough suppressants can provide significant relief for such Antibiotic treatment usually is necessary for 3 to 4 weeks.
animals and may even facilitate ventilation and decrease Even longer treatment may be necessary in some cases, par-
anxiety. Although the doses given in Table 21.1 are the ones ticularly if bronchiectasis or overt pneumonia is present. The
that provide prolonged effectiveness, less frequent adminis- use of antibiotics for the treatment of respiratory tract infec-
tration (i.e., only during times of the day when coughing is tion is also discussed in the section on CIRDC in this chapter
most severe) may preserve some beneficial effect of cough. and in the section on bacterial pneumonia in Chapter 22.
For dogs with severe cough, hydrocodone may provide the Tracheobronchomalacia is discussed later in this chapter,
greatest relief. and pulmonary hypertension is discussed in Chapter 22.
Maropitant may be considered as a cough suppressant in
dogs that cannot tolerate even low dosages of narcotic anti- Prognosis
tussives. Although there was no benefit in reducing airway Canine chronic bronchitis cannot be completely cured. The
inflammation, Grobman and Reinero (2016) reported a prognosis for the control of signs and for a satisfactory
decrease in cough as described by owners of dogs with bron- quality of life in animals is good if owners are conscientious
chitis. Maximal effect may not be seen before 1 to 2 weeks about performing the medical management aspects of care
of treatment. and are willing to adjust treatment over time and treat sec-
ondary problems as they occur.
MANAGEMENT OF COMPLICATIONS
Antibiotics are often prescribed for dogs with chronic bron-
chitis. If possible, confirmation of infection and antibiotic FELINE BRONCHITIS (IDIOPATHIC)
sensitivity information should be obtained by culture of an
airway specimen (e.g., tracheal wash fluid). Because cough in Etiology
dogs with chronic bronchitis often waxes and wanes in sever- Cats with respiratory disease of many origins present with
ity, it is difficult to make a diagnosis of infection on the basis signs of bronchitis or asthma. Cat airways are much more
of the patient’s response to therapy. Furthermore, organ- reactive and prone to bronchoconstriction than those of
isms involved in bronchial infections generally originate dogs. The common presenting signs of bronchitis (i.e., cough,
from the oropharynx. They are frequently gram-negative wheezing, and/or respiratory distress) can occur in cats with
with unpredictable antibiotic sensitivity patterns. The role diseases as varied as lung parasites, heartworm disease, aller-
of Mycoplasma organisms in canine chronic bronchitis is gic bronchitis, bacterial or viral bronchitis, toxoplasmosis,
not well understood. They may be an incidental finding, or idiopathic pulmonary fibrosis, carcinoma, and aspiration
they may be pathogenic. Ideally, antibiotic selection is based pneumonia (Table 21.2). Veterinarians often assume that cats
on results of culture. Antibiotics that are generally effec- with presenting signs of bronchitis or asthma have idiopathic
tive against Mycoplasma include doxycycline, azithromycin, disease because in most cats an underlying cause cannot be
chloramphenicol, and fluoroquinolones. found. However, as with canine chronic bronchitis, a diag-
In addition to the susceptibility of identified organisms, nosis of idiopathic feline bronchitis can be made only by
the ability of candidate antibiotics to penetrate the airway ruling out other active disease. Care should be taken when
secretions to the site of infection should be considered when using the terms feline bronchitis or feline asthma to distin-
selecting an antibiotic. Antibiotics that are likely to reach guish between a presentation consistent with bronchitis in
concentrations effective against susceptible organisms a broad sense and a clinical diagnosis of idiopathic disease.
include fluoroquinolones, azithromycin, chloramphenicol, Cats with idiopathic bronchitis often have some degree of
and possibly amoxicillin with clavulanate. β-Lactam antibi- airway eosinophilia, typical of an allergic reaction. This
otics do not generally reach therapeutic concentrations in author prefers to reserve the diagnosis of allergic bronchitis
airway secretions of healthy (not inflamed) subjects. If used for patients who respond dramatically to the elimination of
for bronchial infection, the high end of the dosage range a suspected allergen (see the section on allergic bronchitis
should be used. later in this chapter).
Doxycycline is often recommended because Mycoplasma A wide variety of pathologic processes can affect indi-
and many Bordetella isolates are susceptible to this drug. It vidual cats with idiopathic bronchitis. Clinically, the range in