Constipation management

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Constipation Management

Bristol Stool Form Scale

Types 1-2 indicate constipation. The goal of treatment is stools resembling Types 3-4.

Definition & Pathophysiology

Patients define constipation not just as decreased frequency, but also as difficulty initiating defecation, passage of firm or small-volume feces, or a sensation of incomplete evacuation. Up to 60% of patients presenting with constipation actually have normal colonic transit - they either have IBS or define constipation in non-frequency terms. In the remainder, the problem is either:

Delayed colonic transit - defect in colonic motility
Outlet disorder - dysfunction of the rectoanal neuromuscular apparatus
Goodman & Gilman's Pharmacological Basis of Therapeutics, p. 1728

Secondary / Reversible Causes to Exclude

Low dietary fiber intake
Medications: opioids, anticholinergics, CCBs, iron supplements, antacids (calcium/aluminum)
Hormonal: hypothyroidism, hyperparathyroidism, diabetes
Neurogenic: Parkinson's, spinal cord lesions, Hirschsprung's disease
Systemic illness: scleroderma, amyloidosis

Step 1: Non-Pharmacologic Measures (First-Line)

Most guidelines recommend these as primary measures:

Dietary fiber: 20-35 g/day - fruits, vegetables, whole grains
Adequate fluid intake
Physical activity
Bowel habit training: regular toilet time, positive reinforcement (especially in children)
Review and reduce constipating medications where possible
Goodman & Gilman's, p. 1732-1734

Step 2: Pharmacologic Management

A. Osmotic Laxatives (First-Line)

Current evidence supports osmotic or stimulant laxatives as first treatment strategies in functional and chronic constipation.

Agent	Mechanism	Dose / Notes
Polyethylene glycol (PEG/Macrogol)	Non-absorbable polymer; retains water osmotically	17 g in 8 oz water/juice daily; first-line for both disimpaction and maintenance
Lactulose	Synthetic disaccharide; hydrolyzed by colonic bacteria to short-chain fatty acids, draws water osmotically	15-30 mL at night; effects in 24-48 h; best alternative if PEG unavailable
Sorbitol	Similar to lactulose; equally efficacious	15-30 mL of 70% solution
Magnesium citrate / Mg hydroxide	Osmotic + stimulates CCK release	4 mL/kg/day; use with caution in renal insufficiency or cardiac disease
Sodium phosphate	Osmotic enema	Avoid in children <2 yrs; risk of acute nephropathy

Harriet Lane Handbook, 23rd ed., p. 423 | Goodman & Gilman's, p. 1843-1844

B. Stimulant (Irritant) Laxatives

Recommended when patients do not respond to osmotic laxatives. They act directly on enterocytes, enteric neurons, and smooth muscle to promote water/electrolyte accumulation and stimulate motility.

Agent	Notes
Bisacodyl (diphenylmethane)	Oral, suppository, or enema. Marketed as enteric-coated tablets (avoid with antacids/milk - premature dissolution). 1-2 suppositories/day
Senna (anthraquinone)	Oral. Frequently used; 2 tbsp at bedtime for opioid-induced constipation prevention
Ricinoleic acid (castor oil)	Anthraquinone derivative; rarely used in modern practice

Use at lowest effective dose for the shortest period necessary. Chronic overuse can cause electrolyte loss, secondary aldosteronism, steatorrhea, protein-losing enteropathy, and osteomalacia.

Goodman & Gilman's, p. 1855-1858

C. Stool Softeners / Emollients

Agent	Mechanism	Notes
Docusate sodium (100 mg twice daily)	Anionic surfactant; lowers stool surface tension, allows aqueous/fatty mixing	Well tolerated but marginal efficacy in chronic constipation; not first-line
Mineral oil	Softens/lubricates stool; interferes with water reabsorption	Risk: impairs fat-soluble vitamin absorption, lipid pneumonitis if aspirated, foreign-body reactions. Avoid in infants and at bedtime

Goodman & Gilman's, p. 1850-1852

D. Bulk-Forming Agents

Agent	Notes
Psyllium, methylcellulose, polycarbophil	Increase stool bulk and water content. Require adequate fluid intake to avoid obstruction. Useful adjuncts but generally not first-line for established constipation

Note: Bulk-forming laxatives should be avoided in chronic intestinal pseudo-obstruction (CIPO) as they increase the load on an already dysmotile colon. - Yamada's Gastroenterology, 7th ed.

E. Secretagogues (for Refractory/Chronic Constipation)

Agent	Mechanism	Use
Lubiprostone	Activates ClC-2 chloride channels in intestinal epithelium; increases fluid secretion	Chronic idiopathic constipation; opioid-induced constipation unresponsive to standard laxatives
Linaclotide / Plecanatide	Guanylate cyclase-C agonists; stimulate intestinal secretion and transit	Chronic idiopathic constipation and IBS-C

F. Prokinetics

Agent	Use
Prucalopride (5-HT4 agonist)	Chronic constipation refractory to laxatives; particularly useful in chronic intestinal pseudo-obstruction

Opioid-Induced Constipation (OIC)

Nearly all patients on opioids develop constipation. Prevention is the preferred strategy - do not wait for constipation to develop.

First-line prevention:

Bulk-forming agents: psyllium 1 tbsp daily
Osmotic laxatives: PEG 1 tbsp daily
Stimulant laxatives: senna 2 tbsp at bedtime

Refractory OIC:

Methylnaltrexone (peripherally restricted mu-opioid antagonist) - reverses OIC without affecting central analgesia; causes laxation within 24 h in placebo-controlled trials
Naloxegol - similar peripherally limited opioid antagonist
Lubiprostone
Harrison's Principles of Internal Medicine, 22nd ed., p. 465 | Goodman & Gilman's, p. 497

Special Populations

Pediatric (Harriet Lane Handbook, 23rd ed.)

Disimpaction:

Oral/NG: PEG - 1 to 1.5 g/kg/day for 3 days (>3 years); or magnesium citrate
Rectal: Saline or mineral oil enemas
Infants (<1 year): Glycerin suppositories; 2-4 oz of 100% prune or pear juice. PEG used off-label. Avoid mineral oil, stimulant laxatives, phosphate enemas

Maintenance therapy (3-12 months):

Daily PEG (first-line)
Lactulose as second-line
Stimulant laxatives and stool softeners as adjuncts
Evidence does not support probiotics
Dietary: increased fruits, vegetables, whole grains, fluids (limit cow's milk)
Behavioral: regular toilet schedule with positive reinforcement; mental health referral if encopresis is a concern
Discontinue therapy gradually only after return of regular bowel movements with good evacuation

Geriatric

Osmotic laxatives (PEG, lactulose, sorbitol) are safe and effective
Avoid sodium phosphate enemas (electrolyte/renal risk)
Review polypharmacy as the primary driver

Renal Impairment

Avoid magnesium-containing preparations (Mg toxicity)
Avoid sodium phosphate (acute nephropathy)
PEG is safe

Home Cleanout Protocol (Harriet Lane, Box 12.1)

Take a stimulant laxative (bisacodyl or senna) with 8 oz liquid per dosing instructions
Drink PEG mixed with water or clear non-carbonated liquid - full amount over 2 hours
1-2 hours after finishing PEG, expect passage of formed/thick brown stool progressing to thinner, clearer stool

Red Flags Warranting Investigation

Constipation with any of these warrants further workup (colonoscopy, imaging, anorectal manometry):

Rectal bleeding / haematochezia
Weight loss, anorexia
Iron-deficiency anemia
New onset in patients >50 years
Family history of colorectal cancer
Failure to respond to 4-6 weeks of laxatives
Suspected outlet disorder (prolonged straining, incomplete evacuation, need for manual maneuvers)

Sources: Goodman & Gilman's Pharmacological Basis of Therapeutics, 14th ed. | Harriet Lane Handbook, 23rd ed. (Johns Hopkins) | Harrison's Principles of Internal Medicine, 22nd ed. (2025)

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