Page 473 - Small Animal Internal Medicine, 6th Edition

CHAPTER 28 General Therapeutic Principles 445

Retention enemas are given so that the material adminis- hyperkalemia), especially in cats and small dogs; but any
tered stays in the colon until it exerts its desired effects (e.g., animal that cannot quickly evacuate the enema is at risk.
VetBooks.ir antiinflammatory retention enemas in animals with IBD, to augment defecation in animals that are not obstructed.
Cathartics and laxatives (Table 28.8) should be used only
water in obstipated animals). Obstipated animals may
require frequent administrations of modest volumes of water
part of lower bowel cleansing before colonoscopy or colonic
(e.g., 20-200 mL, depending on the animal’s size) so that the They are not routinely indicated in small animals except as
water stays in the colon and gradually softens the feces. The surgery.
clinician should avoid overdistending the colon or adminis- Irritative laxatives (e.g., bisacodyl) stimulate defecation
tering drugs that may be absorbed and produce undesirable rather than soften feces. They are often used before colono-
effects. Suspected or pending colonic rupture is a contrain- scopic procedures and in animals that are reluctant to defe-
dication to the use of enemas, but this can be difficult to cate because of an altered environment. They are probably
predict. Animals that have undergone neurosurgery (e.g., inappropriate for long-term use because people who use
hemilaminectomy) and are receiving glucocorticoids, espe- them chronically develop dependence and other colonic
cially dexamethasone, may be at increased risk for colonic problems. A glycerin suppository or a lubricated matchstick
perforation. Animals with colonic tumors and those that is often an effective substitute for an irritative laxative. These
have recently undergone colonic surgery or biopsy should objects are carefully placed in the rectum to stimulate
not receive enemas unless there is an overriding reason. defecation.
Cleansing enemas are designed to remove fecal material. Bulk and osmotic laxatives include a variety of prepara-
They involve repeated administration of relatively large tions: various fibers (especially soluble ones), magnesium
volumes of warm water. In dogs the water is administered by sulfate, lactulose, and, in milk-intolerant animals, ice cream
gravity flow from a bucket or bag held above the animal. The or milk. They promote fecal retention of water and are indi-
enema tube is gently advanced as far as it will easily go into cated in animals that have overly hard stools not caused by
the colon (hopefully to the flexure between the descending ingestion of foreign objects. Fiber is a bulking agent that is
and transverse colon). Between 50 and 100 mL is tolerated incorporated into food and can be used indefinitely. Com-
by most small dogs, 200 to 500 mL by medium-size dogs, mercial diets relatively high in fiber may be used, or existing
and 1 to 2 L by large dogs. Care should be taken to avoid diets may be supplemented with fiber (see p. 434). It is
overdistending or perforating the colon. Enemas are usually important to supply adequate amounts of water so that the
administered to cats with a soft canine male urinary catheter additional fiber does not cause harder-than-normal stools.
and a 50-mL syringe. Cats typically vomit if rapid fluid Too much fiber may cause excessive stool or inappetence
administration causes colonic distention. A suspected or resulting from decreased palatability (a danger for fat cats at
pending colonic perforation is a contraindication to a cleans- risk for hepatic lipidosis). Fiber should not be given to
ing enema. animals with a partial or complete alimentary tract obstruc-
Hypertonic enemas are potentially dangerous and should tion, because impaction may occur.
not be used unless there is a clear-cut and imperative reason Lactulose (Cephulac) was designed to control signs of
to do so. They can cause massive, fatal fluid and electrolyte hepatic encephalopathy, but it is also an effective osmotic
shifts (i.e., hyperphosphatemia, hypocalcemia, hypokalemia, laxative. It is a disaccharide that is split by colonic bacteria

TABLE 28.8
Selected Laxatives, Cathartics, Stool-Softening Agents, and Bulking Agents

DRUG DOSAGE (PO) COMMENTS

Bisacodyl (Dulcolax) 5 mg (small dogs and cats) Do not break tablets.
10-15 mg (larger dogs)
Coarse wheat bran 1-3 tbsp/454 g of food
Canned pumpkin pie filling 1-3 tbsp/day (cats only) Principally for cats.
Dioctyl sodium sulfosuccinate (Colace) 10-200 mg q8-12h (dogs only) Be sure animal is not dehydrated
10-25 mg q12-24h (cats only) when treating.
Lactulose (Cephulac) 1 mL/4.5 kg q8-12h, then adjust dose as Can cause severe osmotic
needed (dogs only) diarrhea.
5 mL q8-12h, then adjust dose as needed
(cats only)
Psyllium (Metamucil) 1-2 tsp/454 g of food Be sure animal has enough water,
or constipation may develop.
PO, Orally.