Chapter 65: Laxatives Flashcards
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
Factor of how often an individual BM and what the consistency of the stool
Normal BM can be 2-3x/day to 1-2x/week
Laxative effect
Production of soft, formed stool over 1 or more days
Relatively mild
Catharsis
Prompt, fluid evacuation of the bowel
Fast and intense
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 (from 2 to 3 times/day to 2 times/wk)
Dietary Fiber
Proper bowel function is highly dependent on dietary fiber (bran is the best source)
Benefits of fiber
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
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 are spent on laxatives
Constipation may be defined as:
Hard stools, infrequent stools, excessive straining, prolonged effort, sense of incomplete evacuation, unsuccessful defecation
Indications for Laxative Use
Obtain fresh stool sample
Empty bowel before treatment or procedure
Expel dead parasites after treatment
Modify effluent from ileostomy or colostomy
Constipation (multiple causes, including pregnancy and opioid use)
Prevent fecal impaction in bedridden patients
Remove poisons
Contraindications to Laxative Use
Abdominal pain, nausea, cramps, or other symptoms of appendicitis, regional enteritis, diverticulitis, or ulcerative colitis
Acute surgical abdomen
Fecal impaction or bowel obstruction
Habitual use
Use with caution in pregnancy and lactation
Classification of Laxatives
Bulk-forming laxatives
Psyllium [Metamucil]
Surfactant laxatives
Docusate sodium [Colace]
Stimulant laxatives
Bisacodyl [Dulcolax]
35-Osmotic laxatives
Milk of magnesia (MOM)
Classification of Laxatives: Therapeutic Effect
Group I: Act rapidly (within 2 to 6 hr) and give stool a watery consistency; useful for preparing bowel for diagnostic procedures or surgery
Group II: Intermediate latency (6 to 12 hr); produce a semifluid stool
Group III: Most frequently abused by the general public; act slowly (1 to 3 days) to produce a soft, formed stool; uses include treating chronic constipation and preventing straining at stool
Bulk-Forming Laxatives
Metamucil
Citrucel
Fibercon
Surfactant Laxatives
Produce a soft stool several days after onset of treatment
Alter stool consistency by lowering surface tension, which facilitates penetration of water into feces
May also act on intestinal wall to (1) inhibit fluid absorption and (2) stimulate secretion of water and electrolytes into intestinal lumen; in this respect, surfactants resemble stimulant laxatives
Colace
Stimulant Laxatives
Ducolax, senna
Two effects on bowel:
Stimulate intestinal motility
Increase amounts of water and electrolytes in intestinal lumen
Widely used and abused
Legitimately used for opioid-induced constipation and for constipation from slow intestinal transit
Osmotic Laxatives
Laxative salts (sodium phosphate, magnesium hydroxide)
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 to 12 hours
High doses: Results in 2 to 6 hours
MOM, miralax, lactulose
Adverse effects
Dehydration: Substantial water loss
Acute renal failure
Sodium retention: Exacerbated heart failure, hypertension, edema
Lubiprostone
Selective chloride channel activator
By activating (opening) chloride channels in epithelial cells lining the intestine, lubiprostone (1) promotes secretion of chloride-rich fluid into the intestine and (2) enhances motility in the small intestine and colon
The result is spontaneous evacuation of a semisoft stool, usually within 24 hours
Mineral oil
Mineral oil: Mixture of indigestible and poorly absorbed hydrocarbons. Laxative action is produced by lubrication. Mineral oil is especially useful when administered by enema to treat fecal impaction
Adverse effects: Lipid pneumonia, anal leakage, and deposition of mineral oil in the liver
Glycerin suppository
Osmotic agent that softens and lubricates hardened, impacted feces
May also stimulate rectal contraction
Evacuation occurs about 30 minutes after suppository insertion
Useful for reestablishing normal bowel function after termination of chronic laxative use
Bowel-Cleansing Products for Colonoscopy
Allow for good visualization of the bowel
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
Combination of sodium picosulfate, magnesium oxide, and citric acid
Polyethylene Glycol—Electrolyte Solutions
CoLyte, GoLYTELY
Volume administered is huge, typically 4 L. Patients must ingest 250 to 300 mL every 10 minutes for 2 to 3 hours. With HalfLytely and MoviPrep, the volume is cut in half
Most common adverse effects are nausea, bloating, and abdominal discomfort
Sodium Phosphate Products
Osmotic laxatives that draw water into intestinal lumen, which softens and swells fecal mass, which stretches intestinal wall to stimulate peristalsis
Adverse effects: Nausea, bloating, abdominal discomfort; risk of dehydration, electrolyte disturbances, and kidney damage
Hyperphosphatemia, which can cause acute, reversible renal damage and possibly chronic, irreversible renal damage
Combination Product
Magnesium oxide/anhydrous citric acid/sodium picosulfate [Prepopik] has been approved for preparation for colonoscopy in adults
Adverse effects: Possible electrolyte and fluid imbalances, renal impairment, seizures, and arrhythmia secondary to electrolyte abnormalities. Caution must be used in patients with reduced renal function. The most common adverse reactions are nausea, headache, and vomiting
Laxative Abuse
Causes
Misconception that bowel movements must occur daily
Can perpetuate their own use
Bowel replenishment after evacuation can take 2 to 5 days; often mistaken for constipation
Consequences
Diminished defecatory reflexes, leading to further reliance on laxatives
Electrolyte imbalance, dehydration, colitis
