What is the best approach to manage a patient presenting with constipation?

Management of Constipation

Start with polyethylene glycol (PEG) 17g dissolved in 8 ounces of liquid once daily as your first-line pharmacological treatment, combined with lifestyle modifications including at least 1.5 liters of fluid daily and regular physical activity. 1, 2

Initial Assessment

Before initiating treatment, evaluate for:

• Alarm symptoms: rectal bleeding, unintentional weight loss, fever, vomiting, or severe abdominal distension that would require further workup 3, 4
• Medication review: discontinue or substitute constipating medications (opioids, anticholinergics, calcium channel blockers, iron supplements) before extensive evaluation 2
• Secondary causes: hypothyroidism, hypercalcemia, diabetes mellitus, neurologic disorders, or mechanical obstruction 1, 5
• Defecation patterns: stool frequency, consistency (using Bristol Stool Scale), straining, sensation of incomplete evacuation, and anorectal blockage 1

First-Line Lifestyle Modifications

Implement these measures alongside pharmacological therapy:

• Fluid intake: ensure at least 1.5 liters of water daily, increased during exercise, hot weather, or illness 2
• Toileting habits: establish regular attempts at defecation 30 minutes after meals to utilize the gastrocolic reflex 2
• Physical activity: encourage regular moderate exercise as tolerated 1, 2
• Fiber supplementation: gradually increase to 14g per 1,000 kcal intake per day (approximately 20-25g daily), titrating slowly over several days to minimize bloating and abdominal discomfort 1, 6

Common pitfall: Fiber alone is often insufficient for chronic constipation and should not delay pharmacological treatment. 7

Pharmacological Treatment Algorithm

Step 1: Polyethylene Glycol (First-Line)

PEG 17g dissolved in 8 ounces of liquid once daily is the gold standard with the strongest evidence base. 1, 2

• Efficacy: increases complete spontaneous bowel movements by approximately 2.9 per week compared to placebo 2
• Mechanism: osmotic laxative that traps water in the intestine 1
• Titration: adjust dose based on symptom response and side effects; no clear maximum dose 1
• Duration: response has been shown to be durable over 6 months 1
• Side effects: bloating, abdominal discomfort, and cramping 1
• When to stop: discontinue if rectal bleeding occurs, nausea/bloating/cramping worsens, diarrhea develops, or no response after 1 week 4

Step 2: Alternative Osmotic Laxatives (If PEG Ineffective)

If PEG fails after adequate trial:

• Lactulose 15g daily: osmotic laxative, only agent studied in pregnancy; bloating and flatulence may be limiting 1, 2
• Magnesium oxide 400-500mg daily: use with caution in renal insufficiency and pregnancy; prior studies used 1,000-1,500mg daily 1
• Milk of magnesia: alternative osmotic option 2

Step 3: Stimulant Laxatives (Add-On or Alternative)

Consider when osmotic laxatives are insufficient:

• Bisacodyl or sodium picosulfate: cost less than $5 monthly 1
• Senna: alternative stimulant option 1
• Use pattern: can be used regularly or PRN; reserve for breakthrough symptoms if preferred 7

Common pitfall: Avoid bulk laxatives (psyllium) in non-ambulatory patients with low fluid intake due to increased risk of mechanical obstruction. 1

Special Populations

Opioid-Induced Constipation

All patients receiving opioid analgesics should be prescribed a concomitant laxative unless contraindicated by pre-existing diarrhea. 1, 2

• First-line: osmotic (PEG) or stimulant laxatives (senna, bisacodyl) 1
• Avoid: bulk laxatives such as psyllium 1
• Consider: combination opioid/naloxone medications to reduce OIC risk 1
• Refractory cases: peripherally acting μ-opioid receptor antagonists (PAMORAs) such as methylnaltrexone or naldemedine 1, 5

Elderly Patients

• Preferred agent: PEG 17g daily due to efficacy and good safety profile 1, 2
• Avoid: liquid paraffin in bed-bound patients or those with swallowing disorders (risk of aspiration lipoid pneumonia) 1, 2
• Caution with: magnesium-containing laxatives due to risk of hypermagnesemia, especially with renal impairment 1
• Monitor: chronic kidney/heart failure patients on diuretics or cardiac glycosides for dehydration and electrolyte imbalances 1

When to Perform Anorectal Testing

Obtain anorectal manometry and balloon expulsion test in patients who do not respond to over-the-counter laxatives after adequate trial (typically 4-8 weeks). 8

This identifies defecatory disorders (dyssynergic defecation/pelvic floor dysfunction), which occur in approximately 40% of patients with chronic constipation. 7

• Treatment for defecatory disorders: pelvic floor retraining by biofeedback therapy rather than escalating laxatives 2
• Efficacy: biofeedback improves symptoms in more than 70% of patients with defecatory disorders 2

Colonic Transit Assessment

If symptoms persist despite adequate laxative therapy and normal anorectal testing:

• Colonic transit study: identifies slow-transit constipation 8
• Management: normal transit and slow-transit constipation can be safely managed with long-term laxative use 2
• Surgical consideration: total colectomy with ileorectal anastomosis only after well-documented slow-transit constipation and failure of aggressive, prolonged trial of laxatives, fiber, and prokinetic agents 2

Rectal Impaction Management

When digital rectal examination identifies full rectum or fecal impaction:

• First-line: suppositories (bisacodyl, glycerin) or enemas 1
• Technique: digital fragmentation and extraction if needed, followed by maintenance bowel regimen 1
• Contraindications to enemas: neutropenia, thrombocytopenia, paralytic ileus, intestinal obstruction, recent colorectal/gynecological surgery, recent anal/rectal trauma, severe colitis, toxic megacolon, undiagnosed abdominal pain, or recent pelvic radiotherapy 1

Red Flags Requiring Further Evaluation

Stop laxative therapy and investigate if:

• Constipation persists beyond 7 days of treatment 3
• Rectal bleeding occurs 3, 4
• Complete failure to have bowel movement 3
• Worsening nausea, bloating, cramping, or abdominal pain 4
• Development of diarrhea (may indicate overflow incontinence from impaction) 4