Laxative Agents

Chapter 50 Laxative Agents

Definition of Constipation

Constipation is an important pathophysiologic condition of both cats and dogs, but primarily of the cat. Constipation is defined as difficult, painful, or reduced defecation over a period of time ranging from days to weeks or months.1 Physical examination findings depend on the severity and pathogenesis of constipation. Dehydration, weight loss, abdominal pain, and mild to moderate mesenteric lymphadenopathy are common findings in cats with idiopathic constipation. It is important to consider an extensive list of differential diagnoses in an individual animal, but it should be kept in mind that most cases are idiopathic, orthopedic, or neurologic in origin (see Chapters 10 and 58).2 Left untreated or poorly monitored, constipation may progress to obstipation (permanent loss of function) and megacolon (permanent loss of form and function).3

Established Laxative Agents

Laxatives promote evacuation of the bowel through stimulation of fluid and electrolyte transport or increases in propulsive motility. Established laxative agents are characterized as bulk-forming, emollient, lubricant, hyperosmotic, or stimulant laxatives, according to their mechanism of action (Table 50-1).3 Newer laxative agents are more specific in their mechanism(s) of action, and include chloride channel activation, guanylate cyclase activation, µ-opioid receptor antagonism, 5-HT4 serotonergic receptor agonism, and neurotrophin-3 activation.57

Table 50-1 Classification, Examples, and Doses of Established and Newer Laxative Agents

Drug Classification and Example Dose
Rectal Suppositories  
Dioctyl sodium sulfosuccinate 1 to 2 pediatric suppositories
Glycerin 1 to 2 pediatric suppositories
Bisacodyl 1 to 2 pediatric suppositories
Warm tap water 5 to 10 mL/kg
Warm isotonic saline 5 to 10 mL/kg
Dioctyl sodium sulfosuccinate 5 to 10 ml/cat
Dioctyl calcium sulfosuccinate 250 mg (12 mL) given per rectum
Mineral oil 5 to 10 mL/cat
Lactulose 5 to 10 mL/cat
Established Laxative Agents
Bulk Laxatives  
Psyllium 1 to 4 tsp mixed with food, every 24 or 12 hours
Canned pumpkin 1 to 4 tsp mixed with food, q24h
Coarse wheat bran 1 to 4 tsp mixed with food, q24h
Emollient Laxatives  
Dioctyl sodium sulfosuccinate 50 mg PO, q24h
Dioctyl calcium sulfosuccinate 50 mg PO, q12 or 24h as needed
Lubricant Laxatives  
Mineral oil 10 to 25 mL PO, q24h
Petrolatum 1 to 5 mL PO, q24h
Hyperosmotic Laxatives  
Lactulose 1 mL per 4.5 kg PO
Polyethylene glycol 25 mL/kg PO q24h as needed
Stimulant Laxatives  
Bisacodyl 5 mg PO q24h
Newer Laxative Agents  
Chloride Channel Activators  
Lubiprostone Safe and effective doses not yet established
Guanylate Cyclase Activators
Linaclotide Safe and effective doses not yet established
µ-Opioid Antagonists  
Methylnaltrexone 0.15 mg/kg SQ q24 to 48h
Alvimopan Safe and effective doses not yet established
Serotonergic 5-HT4 Agonists
Prucalopride 0.01 to 0.2 mg/kg PO q8 to 12h as needed
Neurotrophin-3 Safe and effective doses not yet established

Bulk-Forming Laxatives

Most bulk-forming laxatives are dietary fiber supplements of poorly digestible polysaccharides and celluloses derived principally from cereal grains, wheat bran, and psyllium. Some constipated cats will respond to supplementation of the diet with one of these products, but many require adjunctive therapy (e.g., other types of laxatives or colonic prokinetic agents). Dietary fiber is preferable because it is well tolerated, more effective, and more physiologic than other laxatives. Fiber is classified as a bulk-forming laxative, although it has many other properties. The beneficial effects of fiber in constipation include increased fecal water content, decreased intestinal transit time, and increased frequency of defecation.8,9 Short-chain fatty acids derived from fiber fermentation in the gut have been shown to directly stimulate colonic motility.8,9 Fiber supplemented diets are available commercially, or the pet owner may wish to add psyllium (1 to 4 tsp per meal), wheat bran (1 to 2 tbsp per meal), or pumpkin (1 to 4 tbsp per meal) to canned cat food. To maximize the therapeutic effect, cats should be well hydrated before commencing fiber supplementation. Fiber supplementation is most beneficial in mildly constipated cats, prior to the development of obstipation and megacolon. In obstipated and megacolon cats, fiber may in fact be detrimental. Low-residue diets may be more beneficial in obstipated and megacolonic cats.

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Jul 10, 2016 | Posted by in INTERNAL MEDICINE | Comments Off on Laxative Agents
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