Page 469 - Small Animal Internal Medicine, 6th Edition

CHAPTER 28 General Therapeutic Principles 441

management of gastroparesis (in which it is usually more the dog is unknown but suggested to be 10-40 mg/kg SC
effective than metoclopramide) and small intestinal ileus. It q12-24h.
VetBooks.ir has rarely been reported to be beneficial in dogs with mega- used in dogs with colonic inflammation. This drug is gener-
Salicylazosulfapyridine (sulfasalazine [Azulfidine]) is
esophagus (perhaps because the dogs had gastroesophageal
reflux). Cisapride is no longer available from human phar-
It is a combination of sulfapyridine and 5-aminosalicylic acid.
macies but is generally available from veterinary pharmacies. ally not beneficial in animals with small intestinal problems.
It is typically available only as an oral preparation, but can Colonic bacteria split the molecule, and 5-aminosalicylic
be formulated for parenteral use. It has few significant acid (probably the active moiety) is subsequently “depos-
adverse effects, although intoxication with large doses may ited” on diseased colonic mucosa. Dogs generally receive
cause diarrhea, muscular tremors, ataxia, fever, aggression, 50 to 60 mg/kg divided into three doses daily, but not to
and other central nervous system signs. It should not be used exceed 3 g daily. Sulfasalazine given orally may be effective at
concurrently with drugs that are hepatic P450 inhibitors or lower-than-expected doses if used in combination with glu-
that inhibit P-glycoprotein. Erythromycin stimulates motilin cocorticoids. Anecdotally, 15 to 20 mg/kg/day, sometimes
receptors and enhances gastric motility at doses less than divided into twice-daily doses, is often tolerated by cats,
required for antibacterial activity (i.e., 0.5-1 mg/kg). It may but they must be closely observed for salicylate intoxication
also increase intestinal motility. Nizatidine and ranitidine are (i.e., lethargy, anorexia, vomiting, hyperthermia, tachypnea).
H 2 receptor antagonists that have some gastric prokinetic Some cats that vomit or become hyporexic may tolerate the
effects at routinely administered doses. Bethanechol (Ure- medication if it is given in enteric-coated tablets. Many dogs
choline) is an acetylcholine analog that stimulates intestinal with colitis respond to therapy in 3 to 5 days. However, the
motility and secretion. It produces strong contractions that drug may have to be given for 2 weeks before one decides
can cause pain or injure the animal; hence, it is infrequently that it is ineffective. If signs of colitis resolve, the dose should
used except for increasing urinary bladder contractions. be gradually reduced. If the patient cannot be weaned off the
Obstruction of an outflow area can be a contraindication to drug entirely, the lowest effective dose should be used and
the use of prokinetic drugs because vigorous contractions the animal monitored regularly for drug-induced adverse
against such a lesion may cause pain or perforation. Obstruc- effects (especially those resulting from the sulfa moiety). Sul-
tion of the urinary outflow tract is also a contraindication to fasalazine may cause transient or permanent keratoconjunc-
the use of bethanechol. tivitis sicca. Other possible complications include cutaneous
Pyridostigmine (Mestinon) inhibits acetylcholinesterase vasculitis, arthritis, bone marrow suppression, diarrhea, and
and is used to treat myasthenia gravis. It is preferred over any other problem reported with sulfa drugs or NSAIDs.
physostigmine and neostigmine. It is used for the treatment Olsalazine and mesalamine contain or are metabolized to
of acquired megaesophagus due to localized myasthenia. It 5-aminosalicylic acid but do not have the sulfa, which is
must be used cautiously because overdose may cause toxic- responsible for most of sulfasalazine’s adverse effects. In
ity accompanied by signs of parasympathetic overload (e.g., people they are as effective as sulfasalazine but safer. Olsala-
vomiting, miosis, diarrhea). zine and mesalamine have been used effectively in dogs.
They are given in a dose generally about half that of sulfasala-
zine. Keratoconjunctivitis sicca has also developed in dogs
ANTIINFLAMMATORY AND receiving mesalamine.
ANTISECRETORY DRUGS Glucocorticoids are potentially indicated in animals with
chronic alimentary tract inflammation (e.g., moderate to
Intestinal antiinflammatory or antisecretory drugs (or both) marked inflammatory bowel diseases) that is unresponsive
are indicated for lessening fluid losses due to diarrhea or for to well-designed elimination diets and/or antimicrobial
controlling intestinal inflammation that is unresponsive to therapy. Prednisolone is preferred over prednisone. Rela-
dietary or antibacterial therapy. tively high doses (i.e., prednisolone, 2.2 mg/kg/day PO) are
Bismuth subsalicylate (Pepto-Bismol, Kaopectate) is often used initially, and the dose is tapered to find the lowest
effective in many dogs with acute enteritis (see Table 28.6), effective dose. Dexamethasone is sometimes effective when
probably because of the antiprostaglandin activity of the prednisolone is not, but dexamethasone is much more
salicylate moiety. Its main disadvantages are that the salicy- ulcerogenic than prednisolone. If oral administration is a
late is absorbed (warranting cautious use in cats or dogs problem in a cat, long-lasting steroid injections (e.g., methyl-
receiving nephrotoxic drugs), it turns stools black (mimick- prednisolone acetate) may be tried. Methylprednisolone
ing melena), and it must be administered orally (many appears to be a more effective antiinflammatory than pred-
animals dislike its taste). Bismuth is bactericidal for certain nisolone, requiring only 80% of the dose used when admin-
organisms (e.g., Helicobacter spp.). istering prednisolone. Budesonide (Entocort) is a steroid
Octreotide (Sandostatin) is a synthetic analog of soma- that is largely eliminated from the body by first-pass metabo-
tostatin that inhibits alimentary tract motility and secretion lism in the liver, thus diminishing (but not totally eliminat-
of gastrointestinal hormones and fluids. It has had limited ing) systemic steroid side effects. It is primarily indicated in
use in dogs and cats but might be helpful in selected animals patients who are known to respond to prednisolone but
with intractable diarrhea or lymphangiectasia. The dose in cannot tolerate that steroid’s side effects.