JC Pharmacology Wk 7 Chapter 39

Risk Factors for Constipation

• Decreased levels of physical activity contribute to constipation.
• Female gender increases the risk of constipation.
• Nonwhite individuals are more prone to constipation.
• Advanced age is a risk factor for constipation.
• Low levels of education and income increase the likelihood of constipation.

Constipation Overview

• The cerebral cortex controls the defecation reflex, allowing defecation at appropriate times.
• Voluntary control can inhibit or contract the external anal sphincter to prevent defecation.
• If contraction of the external sphincter is maintained, the defecation reflex dissipates, and the urge to defecate will likely not return until more feces enter the rectum, potentially hours later.
• Frequent suppression of the defecation reflex can lead to its weakening and cause constipation.
• Constipation is a symptom, not a distinct disease.
• Characteristics of constipation include infrequent and painful passing of hard, dry stools.
• A traditional medical definition is three or fewer bowel movements per week.
• Rome III criteria is another method, utilizing a multisymptom checklist, to check for constipation.

Intervention

• Diet, exercise, and fluid intake are important in constipation prevention.
• Increase physical activity and exercise.
• Increase dietary fiber through vegetables, fruits, and cereal grains.
• Drink 6-10 glasses (8 ounces) of fluid daily, unless contraindicated.
• Establish a regular bowel elimination routine (e.g., bathroom immediately after breakfast).
• Understand the importance of diet, exercise, and fluid intake in promoting normal bowel function and preventing constipation.
• Assist patients with constipation and caregivers to increase activity and exercise and intake of dietary fiber (e.g., vegetables, fruits, cereal grains), and to maintain fluid intake.

Laxatives: Types and Actions

• Bulk-forming laxatives (psyllium) work by adding mass to the stool, which stimulates peristalsis and defecation.
  • They need to be taken with water to avoid obstruction.
  • Usually, bulk-forming drugs are most desirable for long-term use
• Lubricant laxatives (mineral oil) lubricate the stool and slow down water absorption from the fecal mass in the colon.
  • They may interfere with fat-soluble vitamin absorption.
  • Aspiration can result in lipid aspiration pneumonia.
• Surfactant laxatives (docusate calcium, docusate sodium) decrease the surface tension of stool.
  • Allows water and fat to penetrate, softening the stool for easier expulsion.
  • They have little true laxative effect.

Cathartics: Types and Actions

• Stimulant cathartics (bisacodyl) irritate the GI mucosa, pulling water into the intestinal lumen, and stimulate peristalsis.
  • They produce a watery stool increasing the risk of fluid, electrolyte, and acid-base imbalances.
  • Stimulant cathartics are the strongest and most abused laxatives.
• Saline cathartics (magnesium citrate, milk of magnesia) increase osmotic pressure in the intestinal lumen.
  • This causes water retention, which distends the bowel and stimulates peristalsis.
  • They produce a semifluid stool increasing the risk of fluid and electrolyte imbalances.

Indications for Use

• Relieving constipation in pregnant patients, older patients, children with megacolon, and patients receiving drugs that decrease intestinal motility (opioid analgesics, anticholinergics).
• Preventing straining during stool in those with coronary artery disease, hypertension, cerebrovascular disease, and hemorrhoids.
• Emptying the bowel for bowel surgery or diagnostics (colonoscopy, barium enema).
• Accelerating elimination of potentially toxic substances from the GI tract (orally ingested drugs or toxic compounds).
• Preventing absorption of intestinal ammonia in hepatic encephalopathy patients.
• Obtaining stool specimen through parasitologic examination.
• Accelerating excretion of parasites after anthelmintic drugs.
• Reducing cholesterol (psyllium products).

Adverse Effects

• Psyllium or any fiber product may cause severe flatulence (gas) and bloating.
  • Also, abdominal cramping and esophageal or bowel obstruction have all been reported.
• Bisacodyl common effects are abdominal pain and cramping, nausea, diarrhea, and weakness.

Additional Agents for Constipation

• Lactulose exerts an osmotic effect, drawing water into the intestinal lumen and stimulating peristalsis.
  • It also treats hepatic encephalopathy by decreasing the production of ammonia.
• Sorbitol is given with sodium polystyrene sulfonate (Kayexalate), for the treatment of hyperkalemia to aid in the expulsion of the potassium-resin complex.
• Lubiprostone helps treat chronic idiopathic constipation in adults.
  • It increases intestinal fluid secretion, stimulating motility and defecation.

Assessments

• Assess patients for current or potential constipation by monitoring signs and symptoms.
• Signs of constipation include:
  • Decreased number and frequency of stools.
  • Passage of dry, hard stools.
  • Abdominal distention and discomfort.
  • Flatulence (expulsion of gas through the rectum).
• Presence of risk factors:
  • Diet with minimal fiber (e.g., small amounts of fruits, vegetables, and whole-grain products).
  • Low fluid intake (e.g., less than 6 to 10 glasses [8 ounces each] daily).
  • Immobility or limited activity.
• Use of drugs that reduce intestinal function and motility (e.g., opioid analgesics, antacids containing aluminum or calcium, anticholinergics, calcium channel blockers, clozapine, diuretics, iron, phenothiazines, cholestyramine, colestipol, sucralfate, tricyclic antidepressants, vincristine).
• Overuse of antidiarrheal agents cause constipation. Conditions that may reduce intestinal function and motility (e.g., depression, eating disorders such as anorexia nervosa, hypothyroidism, hypercalcemia, multiple sclerosis, Parkinson disease, spinal lesions).
• Hemorrhoids, anal fissures, and conditions characterized by painful bowel elimination.
• Older adult or debilitated status.

Implementation and Monitoring

• Assist patients with constipation and caregivers to increasing activity and exercise.
• Increase intake of dietary fiber (e.g., vegetables, fruits, cereal grains).
• Maintain fluid intake
• Drink at least 6 to 10 glasses (8 ounces each) of fluid daily unless contraindicated.
• Establish and maintain a routine for bowel elimination (e.g., the bathroom immediately after breakfast).
• Understand and comply with drug therapy
• Monitor patient responses.
• Record the number, amount, and type of bowel movements.
• Make sure to record vital signs.
• Monitor for hypotension and weak pulse which may indicate deficient fluid volume.

Questions cover initial recommendations for constipation, the importance of water with bulk-forming laxatives, and the mechanism of stimulant cathartics. Also covered are surfactant laxatives and the adverse effects of mineral oil. Risks, long-term solutions, and the defecation reflex are also covered.