What are the treatment options for functional constipation?

Treatment of Functional Constipation

Start with a stimulant laxative (senna or bisacodyl 10-15 mg, 2-3 times daily) as first-line therapy, aiming for one non-forced bowel movement every 1-2 days. 1

Pre-Treatment Assessment

Before initiating any laxative therapy, you must rule out:

• Fecal impaction (perform digital rectal exam) 2, 1
• Bowel obstruction (consider plain abdominal radiograph if clinically indicated) 2, 3
• Metabolic causes: hypercalcemia, hypokalemia, hypothyroidism, diabetes mellitus 2, 1, 3

Stepwise Treatment Algorithm

First-Line: Stimulant Laxative Monotherapy

• Senna or bisacodyl 10-15 mg, 2-3 times daily 2, 1
• Do NOT add stool softeners like docusate—evidence shows no additional benefit when combined with stimulant laxatives 1
• Discontinue any non-essential constipating medications 3

Lifestyle Modifications (Adjunctive, Not Primary)

• Increase fluid intake (at least 2 liters daily if adding fiber) 1, 3, 4
• Increase physical activity within patient's limits, even bed-to-chair mobility 2, 3
• Dietary fiber (20-25g daily) ONLY if adequate fluid intake and physical activity are present 1, 3, 5
• Avoid supplemental medicinal fiber (psyllium/Metamucil) for medication-induced constipation—it is ineffective 1

Common Pitfall: Fiber without adequate hydration worsens constipation and causes bloating. 1, 5

Second-Line: Add Osmotic or Additional Stimulant Laxative

If constipation persists after 1-2 weeks, add ONE of the following:

• Polyethylene glycol (PEG) 2, 1, 3
• Lactulose 2, 1, 3
• Magnesium hydroxide or magnesium citrate 2, 1, 3
• Rectal bisacodyl (twice daily) 2, 1

Note: PEG is preferred in elderly patients (17g/day is safe and effective). 3

Third-Line: Prokinetic Agent for Gastroparesis

If gastroparesis is suspected (relevant for patients on GLP-1 agonists like Mounjaro, which slow gastric emptying):

• Metoclopramide 10-20 mg, 2-3 times daily 2, 1

Fourth-Line: Secretagogues

For persistent constipation unresponsive to standard laxatives:

• Linaclotide 72-145 mcg daily 1, 6
• Lubiprostone 1
• Plecanatide 1

Linaclotide increases complete spontaneous bowel movements (CSBMs) by 1.3 per week compared to placebo in adults, with improvements maintained throughout 12 weeks of treatment. 6

Fifth-Line: Opioid-Induced Constipation (Refractory Cases)

For opioid-induced constipation that has not responded to standard laxative therapy:

• Methylnaltrexone 0.15 mg/kg subcutaneously every other day (maximum once daily) 2, 1, 3

This peripherally acting opioid antagonist relieves constipation while maintaining pain control. 2

Management of Fecal Impaction

If impaction is present:

• Glycerine suppositories 2
• Manual disimpaction (digital fragmentation and extraction) 3
• Follow with implementation of a bowel regimen to prevent recurrence 3

Special Considerations

Defecation Disorders (50% of chronic constipation cases):

• Symptoms alone cannot distinguish defecation disorders from other constipation types 7
• Requires anorectal manometry with balloon expulsion testing 8, 7
• Biofeedback therapy is the specific treatment for paradoxical anal contraction or pelvic floor dyssynergia 7

Elderly/Bedridden Patients:

• Avoid liquid paraffin due to aspiration risk and lipoid pneumonia 3
• Monitor for dehydration and electrolyte imbalances if on diuretics or cardiac glycosides 3

Key Clinical Pitfalls to Avoid

1. Do not rely on fiber supplements alone—they are ineffective for medication-induced constipation without adequate hydration 1, 5
2. Do not add stool softeners to stimulant laxatives—no additional benefit 1
3. Reassess for impaction or obstruction if constipation persists despite treatment 1
4. Do not expect daily bowel movements—the goal is one non-forced bowel movement every 1-2 days 2, 1