Page 355 - Small Animal Internal Medicine, 6th Edition

CHAPTER 21 Disorders of the Trachea and Bronchi 327

achieved by maintaining systemic hydration. Therefore also improve mucociliary clearance, decrease fatigue of
diuretic therapy is not recommended in these patients. For respiratory muscles, and inhibit the release of mast cell
VetBooks.ir severely affected dogs, placing the animal in a steamy bath- mediators of inflammation. The potential beneficial effects
of theophylline beyond bronchodilation may be of particular
room or in a room with a vaporizer daily may provide symp-
tomatic relief, although the moisture does not penetrate very
(i.e., likely to bronchospasm) as those of cats and people.
deeply into the airways. Nebulization of saline will allow importance in dogs because their airways are not as reactive
moisture to go more deeply into the lungs. This technique is However, theophylline alone is rarely sufficient to control the
discussed further in the section on bacterial pneumonia in clinical signs of chronic bronchitis except in mild cases
Chapter 22. Another advantage associated with theophylline is that
Patients that are overweight and/or unfit may benefit plasma concentrations of drug can be easily measured by
from weight loss (see Chapter 51) and exercise. Exercise commercial diagnostic laboratories. A disadvantage of the-
should be tailored to the dog’s current fitness level and degree ophylline is that other drugs, such as fluoroquinolones, can
of pulmonary dysfunction to keep from causing excessive delay its clearance, causing signs of theophylline toxicity if
respiratory efforts or even death. Observing the dog during the dosage is not reduced by one third to one half, or the
specific exercise, such as a short walk, while in the client’s dosage interval doubled. Potential adverse effects include
presence may be necessary to make initial recommenda- gastrointestinal signs, cardiac arrhythmias, nervousness, and
tions. Instructing clients in measurement of respiratory rate, seizures. Serious adverse effects are extremely rare at thera-
observation of mucous membrane color, and signs of peutic concentrations.
increased respiratory effort will improve their ability to Variability in sustained plasma concentrations has been
assess the dog’s status during exercise. noted for different theophylline products. At the time of this
writing, only immediate-acting products are commercially
DRUG THERAPIES available. If beneficial effects are not seen at the initial dosage
Medications to control clinical signs include bronchodila- selected, if the patient is predisposed to adverse effects, or if
tors, glucocorticoids, and cough suppressants. adverse effects occur, plasma theophylline concentrations
Theophylline, a methylxanthine bronchodilator, has been should be measured. Therapeutic peak concentration for
used for years for the treatment of chronic bronchitis in bronchodilation, based on data from people, ranges from 10
people and dogs (Box 21.4). This drug became unpopular to 20 µg/mL, whereas antiinflammatory effects may occur at
with physicians when newer bronchodilators with fewer side 5 to 10 µg/mL (Barnes, 2003). To confirm that plasma con-
effects became available. However, research in people sug- centrations are being maintained in this range, blood is col-
gests that theophylline is effective in treating the underlying lected immediately before the next scheduled dose.
inflammation of chronic bronchitis, even at concentrations Sympathomimetic drugs are preferred by some clinicians
below those resulting in bronchodilation (hence, reducing as bronchodilators (see Box 21.4). Terbutaline and albuterol
side effects), and that the antiinflammatory effects may be are selective for β2-adrenergic receptors, lessening their
synergistic with those of glucocorticoids. Theophylline may cardiac effects. Potential adverse effects include nervousness,
tremors, hypotension, and tachycardia. Clinical use of bron-
chodilators delivered by MDI, such as albuterol and ipratro-
pium (a parasympatholytic), has not been investigated for
BOX 21.4 dogs with chronic bronchitis.
Glucocorticoids are generally the most effective treatment
Common Bronchodilators for Use in Cats and Dogs
for controlling the signs of chronic bronchitis and may slow
Methylxanthines the development of permanent airway damage by decreasing
Aminophylline inflammation. They may be particularly helpful in dogs with
Cat: 5 mg/kg PO q12h eosinophilic airway inflammation. Potential negative effects
Dog: 11 mg/kg PO q8h include increased susceptibility to infection in dogs already
Theophylline base (immediate release) impaired by decreased airway clearance; a tendency toward
Cat: 4 mg/kg PO q12h obesity, hepatomegaly, and muscle weakness that may
Dog: 9 mg/kg PO q8h adversely affect ventilation; and pulmonary thromboembo-
lism. Therefore short-acting products are used, the dose is
Sympathomimetics tapered to the lowest effective one, and the drug is discon-
Terbutaline tinued if no beneficial effect is seen.
Cat: 8 − of 2.5 mg tablet/cat PO q12h; or Prednisone is initially given at a dose of 0.5 to 1 mg/kg
1
1
4
0.01 mg/kg SC; can repeat once
Dog: 1.25-5 mg/dog PO q8-12h orally q12h, with a positive response expected within 1 week.
Albuterol The initial dosage is continued until the cough has resolved
Cat and dog: 20-50 µg/kg PO q8-12h (0.02- or its intensity and frequency have reached a plateau. The
0.05 mg/kg), beginning with lower dose subsequent taper should be slow, until the least effective dose
is reached (ideally 0.5 mg/kg orally q48h or less of predni-
PO, By mouth; SC, subcutaneously. sone). Dogs with highly motivated owners, and dogs that