What is the recommended treatment for an adult with severe constipation characterized by fewer than three spontaneous bowel movements per week, hard stools, and a sense of incomplete evacuation?

Treatment for Severe Constipation

Start with polyethylene glycol (PEG) 17 grams once daily as first-line therapy, and if this fails after 1-2 weeks, proceed to anorectal testing (manometry and balloon expulsion) to identify a defecatory disorder before escalating to prescription agents. 1

Initial Therapeutic Approach

First-Line Laxative Therapy

• PEG is the recommended first-line osmotic laxative with strong evidence showing it increases complete spontaneous bowel movements (CSBMs) by 2.9 per week compared to placebo, with moderate certainty of evidence. 1
• Dose PEG at 17 grams (one packet) dissolved in 8 ounces of liquid once daily; response is typically seen within the first week and maintained over 6 months. 1
• Stimulant laxatives (bisacodyl or sodium picosulfate 10 mg once daily) are equally recommended as first-line agents with strong recommendation and moderate quality evidence, and ranked first in network meta-analysis at 4 weeks. 1, 2
• Common side effects of PEG include abdominal distension, loose stools, flatulence, and nausea; serious adverse events are rare. 1

When to Suspect a Defecatory Disorder

• Prolonged excessive straining with soft stools is the hallmark clue that points to dyssynergic defecation rather than slow transit. 1, 3
• The need for digital evacuation or manual perineal/vaginal pressure to facilitate stool passage strongly indicates pelvic floor dysfunction. 1, 3
• Sensation of incomplete evacuation despite daily bowel movements suggests a defecatory disorder, not simple constipation. 1, 3

Diagnostic Testing Algorithm for Non-Responders

Anorectal Testing First

• Perform anorectal manometry and balloon expulsion test before any colonic transit studies in patients who fail 1-2 weeks of over-the-counter laxatives. 1, 3
• Digital rectal examination should assess resting anal sphincter tone, puborectalis contraction during squeeze, paradoxical contraction during simulated defecation, and perineal descent. 1, 3
• Failure to expel a water-filled balloon within 1-3 minutes is diagnostic of a defecatory disorder. 3

Colonic Transit Studies Only After Excluding Defecatory Disorder

• Do not order colonic transit studies before anorectal testing, because defecatory disorders can cause secondary slow transit that improves once the primary evacuation problem is treated. 1, 3
• Reserve colonic transit measurement (radiopaque markers or scintigraphy) for patients with normal anorectal testing or those whose symptoms persist despite biofeedback therapy for a confirmed defecatory disorder. 1, 3

Definitive Treatment Based on Diagnosis

For Confirmed Defecatory Disorder (Dyssynergic Defecation)

• Biofeedback therapy is the first-line definitive treatment with strong recommendation and high-quality evidence, achieving success rates of 70-80% in clinical trials. 3
• Biofeedback uses visual or auditory feedback to train patients to relax pelvic floor muscles during straining, restoring normal recto-anal coordination through operant conditioning. 3
• Laxatives alone are insufficient for defecatory disorders and will not address the underlying evacuation problem. 3, 4

For Normal or Slow Transit Constipation Without Defecatory Disorder

Second-Line Prescription Agents (After Laxative Failure)

• Prucalopride 2 mg once daily is the most efficacious prescription agent at 12 weeks, ranked first in network meta-analysis, with 33% of patients achieving ≥3 CSBMs per week versus 10% with placebo. 5, 2
• Prucalopride is a selective 5-HT4 receptor agonist that increases colonic motility and accelerates transit; median time to first CSBM ranges from 1.4 to 4.7 days. 5
• Linaclotide 290 mcg once daily is an intestinal secretagogue that acts on chloride channels, with similar efficacy to prucalopride at 12 weeks (P-score 0.76 vs 0.71). 2
• Lubiprostone 24 mcg twice daily increases SBM frequency from baseline by 3.9-4.1 per week at 4 weeks, with 57-63% of patients experiencing an SBM within 24 hours of first dose. 6

Choosing Among Prescription Agents

• For patients who previously failed laxatives, prucalopride is likely the most efficacious option based on trials that specifically recruited laxative non-responders. 2
• Lubiprostone is FDA-approved for chronic idiopathic constipation and has demonstrated durable response over 4 weeks with maintained efficacy during continued treatment. 6
• Cost considerations favor generic options when available; prucalopride and linaclotide have similar efficacy profiles at 12 weeks. 2

Special Considerations and Pitfalls

Opioid-Induced Constipation

• If the patient is taking chronic opioids, this is a distinct entity requiring different management. 1, 3
• First-line treatment remains osmotic laxatives (PEG 17-34 g/day) or stimulant laxatives (5-15 mg/day) with strong recommendation and moderate quality evidence. 1
• If laxatives fail, use peripherally acting μ-opioid receptor antagonists (PAMORAs): naloxegol 0.2 mg/day (strong recommendation, moderate evidence) or naldemedine 12.5-25 mg/day (strong recommendation, moderate evidence). 1
• PAMORAs block opioid receptors in the gut without affecting central analgesia, directly counteracting the mechanism of opioid-induced constipation. 1, 3

Critical Pitfalls to Avoid

• Do not assume daily bowel movements exclude constipation; reduced stool frequency correlates poorly with delayed colonic transit, and patients with daily movements can still have severe constipation with incomplete evacuation. 1, 4
• Do not overlook fecal impaction with overflow incontinence; soiling represents liquid stool leaking around retained hard fecal matter and requires rectal disimpaction with small enemas before other interventions. 4
• Do not order colonoscopy unless alarm features are present (blood in stools, anemia, unintentional weight loss, sudden onset) or age-appropriate colon cancer screening has not been performed. 1, 3
• Do not perform metabolic testing (glucose, calcium, TSH) routinely; reserve these for patients with other clinical features suggesting endocrine or metabolic disorders. 1, 3

When to Refer to Gastroenterology

• Failure to respond to over-the-counter laxatives and fiber supplementation after 1-2 weeks. 3
• Suspected defecatory disorder based on history (straining with soft stools, need for manual maneuvers) or abnormal digital rectal examination. 3
• Presence of alarm features requiring colonoscopy and specialized evaluation. 1, 3
• Need for anorectal manometry, balloon expulsion testing, or biofeedback therapy. 3