Chapter 65: Laxatives

Question 1

Laxatives

Answer 1

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

Question 2

Laxative effect

Answer 2

Production of soft, formed stool over 1 or more days

Relatively mild

Question 3

Catharsis

Answer 3

Prompt, fluid evacuation of the bowel

Fast and intense

Question 4

Function of the Colon

Answer 4

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)

Question 5

Dietary Fiber

Answer 5

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

Question 6

Constipation

Answer 6

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

Question 7

Indications for Laxative Use

Answer 7

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

Question 8

Contraindications to Laxative Use

Answer 8

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

Question 9

Classification of Laxatives

Answer 9

Bulk-forming laxatives
Psyllium [Metamucil]

Surfactant laxatives
Docusate sodium [Colace]

Stimulant laxatives
Bisacodyl [Dulcolax]

35-Osmotic laxatives
Milk of magnesia (MOM)

Question 10

Classification of Laxatives: Therapeutic Effect

Answer 10

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

Question 11

Bulk-Forming Laxatives

Answer 11

Metamucil

Citrucel

Fibercon

Question 12

Surfactant Laxatives

Answer 12

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

Question 13

Stimulant Laxatives

Answer 13

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

Question 14

Osmotic Laxatives

Answer 14

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

Question 15

Lubiprostone

Answer 15

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

Question 16

Mineral oil

Answer 16

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

Question 17

Glycerin suppository

Answer 17

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

Question 18

Bowel-Cleansing Products for Colonoscopy

Answer 18

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

Question 19

Polyethylene Glycol—Electrolyte Solutions

Answer 19

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

Question 20

Sodium Phosphate Products

Answer 20

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

Question 21

Combination Product

Answer 21

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

Question 22

Laxative Abuse

Answer 22

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