Page 360 - Small Animal Internal Medicine, 6th Edition

332 PART II Respiratory System Disorders

BRONCHODILATORS
Cats that require relatively large quantities of glucocorticoids
VetBooks.ir to control clinical signs, that react unfavorably to glucocor-
ticoid therapy, or that suffer from periodic exacerbations of
signs can benefit from bronchodilator therapy. Recom-
mended doses of these drugs are listed in Box 21.4.
This author prefers to use theophylline because it is inex-
pensive and often is effective with once-daily administration;
moreover, the plasma concentrations can be easily measured
for monitoring of difficult cases. Additional properties of
theophylline, potential drug interactions, and adverse effects
are described in the previous section on canine chronic
bronchitis.
The pharmacokinetics of theophylline products are differ-
ent in cats than in dogs, resulting in different dosages (see
FIG 21.4
Administering drugs by metered dose inhaler (MDI) to a cat. Box 21.4). Variability in sustained plasma concentrations in
The mask and chamber apparatus is the Aerokat (Trudell both species has been found for different manufacturers of
Medical International, London, Ontario, Canada). theophylline products, and long-acting products are not cur-
rently available. If beneficial effects are not seen, if the patient
is predisposed to adverse effects, or if adverse effects occur,
plasma theophylline concentrations should be measured.
the cat’s face, with the mouth and nose covered completely, Therapeutic peak concentrations, based on data from human
and is held in place while the cat takes 7 to 10 breaths, subjects, are 10 to 20 µg/mL. Plasma for determination of
inhaling the drug into its airways. Excellent videotaped these concentrations should be collected immediately before
examples of clients treating their cats are readily available by the next scheduled dose.
web search. Sympathomimetic drugs can also be effective bronchodi-
The following treatment schedule has been recommended lators. Terbutaline is selective for β2-adrenergic receptors,
(Padrid, 2000): cats with mild daily symptoms should receive lessening its cardiac effects. Potential adverse effects include
220 µg of fluticasone propionate by MDI twice daily and nervousness, tremors, hypotension, and tachycardia. It can
albuterol by MDI as needed. The maximal effect of flutica- be administered subcutaneously for the treatment of respira-
sone is not expected until after 7 to 10 days of treatment. tory emergencies; it can also be administered orally. Note
Cats with moderate daily symptoms should receive treat- that the recommended oral dose for cats (one eighth to one
ments with MDI as described for mild symptoms; in addi- fourth of a 2.5-mg tablet; see Box 21.4) is lower than the
tion, prednisolone is administered orally for 10 days (1 mg/ commonly cited dose of 1.25 mg/cat. The subcutaneous dose
kg q12h for 5 days, then q24h for 5 days). For cats with severe is lower still: 0.01 mg/kg, repeated once in 5 to 10 minutes
symptoms, dexamethasone is administered once (0.5-1 mg/ if necessary.
kg, intravenously), albuterol is administered by MDI every Bronchodilators can be administered to cats by MDI for
30 minutes for up to 4 hours, and oxygen is administered. the immediate treatment of acute respiratory distress (asthma
Once stabilized, these cats are prescribed 220 µg of flutica- attack). Cats with idiopathic bronchitis are routinely pre-
sone propionate by MDI every 12 hours and albuterol by scribed an albuterol MDI, a spacer, and a mask (see the
MDI every 6 hours as needed. Oral prednisolone is admin- section on glucocorticoids for details) to be kept at home for
istered as needed. emergencies.
Studies using cats with experimentally induced allergic
bronchitis have demonstrated beneficial effects with a lower OTHER POTENTIAL TREATMENTS
dosage of 44 µg/puff (Cohn et al., 2010). This form of bron- A therapeutic trial with an antibiotic effective against Myco-
chitis may be less complicated than that seen in clinical plasma is considered because of the difficulty in document-
patients, so I prefer to begin treatment with higher concen- ing infection with this organism. Doxycycline (5 mg/kg
trations and then taper to the least effective dose. Fluticasone orally q12h or 10 mg/kg q24h) is administered for 14 days
is also available at 110 µg/puff, which is a reasonable com- as a therapeutic trial. For cats that are difficult to medi-
promise for clinically stable cats. cate, azithromycin (5-10 mg/kg orally q12h for 1 day, then
Disturbing findings were reported from a study by every 3 days) can be tried. If a Mycoplasma is isolated from
Cocayne et al. (2011), indicating that 7 of 10 cats with natu- airway specimens or if a therapeutic response is seen, pro-
rally occurring bronchitis that had resolution of clinical signs longed treatment for months may be required to eliminate
during treatment with oral prednisolone had detectable infection. Further study is needed. Remember that admin-
airway inflammation based on BAL cytology. The long-term istration of doxycycline should always be followed by a
clinical significance of the persistent inflammation is not yet bolus of water to minimize the incidence of esophageal
known, but this matter deserves further study. stricture. In addition to antibacterial effects, evidence is