Page 470 - Small Animal Internal Medicine, 6th Edition

442 PART III Digestive System Disorders

Glucocorticoids are often beneficial in cats with inflam- 6 mg/m is administered daily for up to three weeks, and
2
matory bowel disease (IBD), but they may worsen intes- then the dose is reduced. A reasonable starting dose in cats
VetBooks.ir tinal disease in some dogs and cats. Iatrogenic Cushing is 1 mg twice weekly for cats weighing less than 3.2 kg and
syndrome primarily occurs in dogs but can develop in cats
2 mg twice weekly for cats weighing more than that. Benefi-
that are grossly overdosed. It is important to have a diag-
seen, the dose should then be decreased very slowly over the
nosis before using high-dose prednisolone therapy because cial effects may not be seen for 4 to 5 weeks. If a response is
some diseases that mimic steroid-responsive lymphocytic next 2 to 3 months. The animal should be monitored for
colitis (e.g., histoplasmosis) are absolute contraindications myelosuppression.
to glucocorticoid therapy. Although more common in Azathioprine (Imuran) is used only in dogs (50 mg/m
2
the southeastern United States and the Ohio River Valley, PO, daily or every other day), never cats. For smaller dogs a
histoplasmosis has been diagnosed in patients residing in 50-mg azathioprine tablet is typically crushed and suspended
nonendemic areas. in a liquid (e.g., 15 mL of a vitamin supplement) to allow
Retention enemas of glucocorticoids or 5-aminosalicylic more accurate dosing. The suspension must be mixed well
acid are rarely indicated in animals with severe distal colitis before each dosing. Every-other-day dosing is much safer
unresponsive to other medications. The dose is estimated but takes much longer (i.e., 2-5 weeks) than every-day dosing
from the human dose. These enemas place large doses of an to see clinical effects. Side effects in dogs may include hepatic
antiinflammatory agent directly on the affected area while disease, pancreatitis, and bone marrow suppression.
minimizing systemic effects. Contraindications to their use
are the same as those for systemic administration of the
active ingredient of the enema. ANTIBACTERIAL DRUGS
Immunosuppressive therapy (e.g., cyclosporine, chloram-
bucil, azathioprine) is indicated in animals with severe IBD In dogs and cats with gastrointestinal problems, antibiotics
that is unresponsive to glucocorticoid, dietary, antimicrobial, are primarily indicated if aspiration pneumonia, fever,
and cobalamin therapy. It is also used in animals with severe a leukogram suggestive of sepsis, severe neutropenia,
disease in which it is in the animal’s best interest to use antibiotic-responsive enteropathy (sometimes also called
aggressive immunosuppressive therapy initially. These drugs “dysbiosis”), clostridial colitis, or symptomatic Helicobacter
should be used only in patients with a definitive diagnosis. gastritis is being treated. Animals with an acute abdomen
Immunosuppressive therapy can be more efficacious than may reasonably be treated with antibiotics while the nature
glucocorticoid therapy alone and allows glucocorticoids to of the disease is being defined. Colitis can be a reasonable
be given at lower doses and for shorter periods, thereby indication for amoxicillin (22 mg/kg PO q12h) or tylosin
decreasing their adverse effects. However, the possibility (10-20 mg/kg PO per day) if clostridial colitis is strongly
of adverse effects from these drugs usually limits their use suspected, but most animals with acute gastroenterocolitis
to animals with severe disease. The reader is referred to of unknown cause (including those with acute hemorrhagic
Chapter 72 for additional information on immunosuppres- diarrheal syndrome—previously called hemorrhagic gastro-
sive therapy. enteritis) do not benefit from antibiotic therapy. Routine use
Cyclosporine (Atopica) is a potent immunosuppressive of antimicrobials in animals with alimentary tract disorders
drug sometimes used in dogs with IBD, lymphangiectasia, is discouraged unless the patient is at high risk for infection
and perianal fistulas. The dose is 3 to 6 mg/kg PO every 12 or is being treated for a specific disorder responsive to
hours, but erratic bioavailability requires therapeutic drug antibiotics.
monitoring in nonresponding patients, usually after 8 to 10 Nonabsorbable aminoglycosides (e.g., neomycin) are
days of therapy. There is considerable variation in the bio- generally not indicated unless an infection known to be sen-
availability of different preparations of cyclosporine. It may sitive to the drug (e.g., campylobacteriosis) is strongly sus-
be administered intravenously in vomiting patients, but then pected. Metronidazole (10-15 mg/kg PO q24h) has been
the initial dose should probably be decreased by 50%. commonly used for a variety of gastrointestinal diseases,
Because of its considerable expense, it is sometimes admin- most of which were probably inappropriate. Metronidazole
istered with low doses of ketoconazole (3-5 mg/kg PO q12h), is sometimes successful for suspected ARE, and some dogs
which inhibits metabolism of cyclosporine and in turn and cats diagnosed with IBD respond better to metronida-
allows the use of lower doses at less expense to the client. zole than to glucocorticoids supporting the hypothesis that
Animals receiving too much cyclosporine usually first show the “IBD” was probably ARE. Adverse effects are uncommon
hyporexia, which can be confusing when dealing with but may include salivation (because of its taste), vomiting,
patients with gastrointestinal disease that are hyporexic to central nervous system abnormalities (e.g., central vestibular
begin with. signs), and perhaps neutropenia. These adverse effects
Oral chlorambucil is an alkylating agent used in dogs with usually resolve after withdrawing the drug. Cats sometimes
severe alimentary tract inflammation and sometimes lym- accept oral suspensions better than the 250-mg tablets,
phangiectasia, and in cats with severe IBD. It is typically which must be cut and have an unpleasant taste. Metronida-
administered with glucocorticoids initially. Chlorambucil zole is potentially carcinogenic in some species, but there is
has fewer adverse effects than azathioprine. In dogs, 4 to no evidence of risk in dogs and cats.