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Chapter 79

Chapter 79. Laxatives. Laxatives. Used to ease or stimulate defecation Soften the stool Increase stool volume Hasten fecal passage through the intestine Facilitate evacuation from the rectum Misuse comes from misconceptions of what constitutes normal bowel function.

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Chapter 79

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  1. Chapter 79 Laxatives

  2. Laxatives • Used to ease or stimulate defecation • Soften the stool • Increase stool volume • Hasten fecal passage through the intestine • Facilitate evacuation from the rectum • Misuse comes from misconceptions of what constitutes normal bowel function

  3. Laxative Effect vs. Catharsis • Laxative effect • Production of soft, formed stool over a period of 1 or more days • Relatively mild • Catharsis • Prompt, fluid evacuation of the bowel • Fast and intense

  4. Function of the Colon • Absorbs water and electrolytes • Absorption of nutrients is minimal • 1500 mL of fluid enters colon each day • 90% of fluid is absorbed • Delayed transport through colon causes excessive fluid absorption and hard stool • Frequency of bowel elimination varies widely (2–3 times/day to 2 times/wk)

  5. Dietary Fiber • Proper function of bowel is highly dependent on dietary fiber (bran is best source) • Absorbs water: softens feces and increases size • Can be digested by colonic bacteria whose growth increases fecal mass • Low-fiber diet: frequent cause of constipation

  6. Constipation • One of the most common GI disorders • People seek medical help for constipation in the United States at least 2.5 million times a year • Hundreds of millions of dollars a year spent on laxatives • Constipation may be defined as • Hard stools, infrequent stools, excessive straining, prolonged effort, sense of incomplete evacuation, unsuccessful defecation

  7. Indications for Laxative Use • Obtaining fresh stool sample • Before treatment/procedure preparation • Expelling dead parasites after treatment • Constipation (multiple causes, including pregnancy and opioid use) • Preventing fecal impaction in bedridden patients • Removing poisons

  8. Contraindications of Laxative Use • Individuals experiencing abdominal pain, nausea, cramps, or other symptoms of appendicitis, regional enteritis, diverticulitis, and ulcerative colitis • Acute surgical abdomen • Fecal impaction or bowel obstruction • Habitual use • Use with caution in pregnancy and lactation

  9. Classification of Laxatives • Bulk-forming laxatives • Psyllium (Metamucil) • Surfactant laxatives • Docusate sodium (Colace) • Stimulant laxatives • Bisacodyl (Dulcolax) • Osmotic laxatives • Milk of magnesia (MOM)

  10. Bulk-Forming Laxatives • Function similarly to dietary fiber: swell with water to form a gel to soften fecal mass and increase mass • Preferred treatment for temporary treatment of constipation • Used for diverticulosis and irritable bowel syndrome • Adverse effects are minimal • Esophageal obstruction

  11. Surfactant Laxatives • Two effects on bowel • Stimulate intestinal motility • Increase quantities of water and electrolytes in the intestinal lumen • Widely used and abused • Legitimately used for opioid-induced constipation and for constipation from slow intestinal transit

  12. Osmotic Laxatives • Laxative salts (magnesium and sodium) • Poorly absorbed salts that draw water into intestinal lumen; fecal mass softens and swells, wall stretches, and peristalsis is stimulated • Low doses: results in 6–12 hours • High doses: results in 2–6 hours

  13. Osmotic Laxatives • Adverse effects • Dehydration: substantial water loss • Renal decline: toxicity • Sodium retention: exacerbated heart failure, hypertension, edema

  14. Other Laxatives • Lubiprostone • Selective chloride channel activators • Glycerin suppository • Mineral oil

  15. Bowel-Cleansing Products for Colonoscopy • Allow for good visualization of the bowel • Two kinds of bowel cleansers • Both equally effective • Sodium phosphate • Hypertonic with body fluids • Can cause dehydration and electrolyte disturbance • Possibility of renal damage • Polyethylene glycol (PEG) plus electrolytes (ELS) • Isotonic with body fluids • Requires ingestion of large volume of bad-tasting liquid

  16. Laxative Abuse • Causes • Misconception that bowel movements must occur daily • Can perpetuate their own use • Bowel replenishment after evacuation can be 2–5 days; often mistaken for constipation • Consequences • Diminished defecatory reflexes, leading to further reliance on laxatives • Electrolyte imbalance, dehydration, and colitis

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