What is the recommended stepwise treatment for chronic constipation in adults?

Stepwise Treatment for Chronic Idiopathic Constipation in Adults

Start with polyethylene glycol (PEG) 17 grams once daily as first-line pharmacologic therapy for chronic idiopathic constipation in adults, as it has strong evidence for efficacy with moderate certainty and durable response over 6 months. 1

Initial Assessment and Baseline Measures

Before initiating pharmacologic therapy, ensure adequate fluid intake, particularly in patients drinking less than the median daily fluid intake, as those in the lowest quartile for fluid consumption are more likely to be constipated. 1 Standard fiber supplements should be taken with 8-10 ounces of fluid. 1

Step 1: Fiber Supplementation (Mild Constipation)

For patients with mild-to-moderate symptoms, especially those with dietary fiber deficiency:

• Psyllium is the preferred fiber supplement based on the best available data, though quality remains low. 1
• Fiber increases stool weight through water retention and bacterial fermentation, which secondarily reduces transit time. 1
• Avoid wheat bran in finely ground powder form, as it can decrease stool water content and paradoxically harden stool. 1
• Water-soluble fibers like pectin have minimal effect on stool weight and are not appropriate for constipation treatment. 2
• The chief side effect is flatulence. 1

Important caveat: Fiber supplements like Metamucil are unlikely to control opioid-induced constipation and are not recommended for that indication. 1

Step 2: Polyethylene Glycol (PEG) - First-Line Pharmacologic Therapy

The AGA/ACG guideline strongly recommends PEG over management without PEG for chronic idiopathic constipation. 1

Dosing and Administration:

• Start with 17 grams (one capful) of PEG 3350 once daily, mixed in 4-8 ounces of liquid. 3
• If insufficient response after 1-2 weeks, titrate dose upward based on symptom response. 3
• Response is durable over 6 months of continuous use. 1, 3

Expected Side Effects:

• Abdominal distension, loose stool, flatulence, and nausea (generally mild to moderate). 1, 3

Combination Strategy:

• Fiber supplementation can be used before PEG for mild constipation or in combination with PEG. 1, 3

Critical Safety Warning:

• Use PEG only under direct physician supervision in patients with chronic kidney disease due to risk of fluid and electrolyte disturbances. 3

Step 3: Alternative Osmotic Laxatives (If PEG Fails or Is Not Tolerated)

If constipation persists despite PEG:

• Lactulose 30-60 mL daily (produces osmotic diarrhea of low pH). 1
• Magnesium hydroxide 30-60 mL daily for rapid bowel evacuation. 1
• Magnesium citrate as alternative osmotic agent. 1

Critical pitfall: Avoid magnesium-based laxatives in any patient with renal insufficiency due to hypermagnesemia risk. 4, 3

Step 4: Stimulant Laxatives (Add-On Therapy)

If inadequate response to osmotic laxatives alone:

• Senna (sennosides) 2 tablets every morning; maximum 8-12 tablets per day. 1
• Bisacodyl 2-3 tablets PO daily or suppository daily. 1
• Stimulant laxatives increase intestinal motility by stimulating the myenteric plexus and inhibiting colonic water absorption. 1
• Caution: Avoid in intestinal obstruction; excessive use causes diarrhea and hypokalemia. 1

Step 5: Rescue Therapy for Persistent Constipation

Before escalating, reassess for obstruction and check for fecal impaction. 1

Additional agents to consider:

• Sorbitol 30 mL every 2 hours × 3, then as needed. 1
• Fleet, saline, or tap water enema for acute relief. 1
• Metoclopramide 10-20 mg PO as prokinetic agent. 1

Step 6: Prescription Secretagogues (Refractory Cases)

For patients failing conventional laxatives:

• Lubiprostone may provide additional benefit, particularly for abdominal pain relief. 3
• Prucalopride (5-HT4 receptor agonist) is effective for constipation without cardiac risks. 1

Special Populations

Opioid-Induced Constipation:

• Prophylactic stool softener plus stimulant laxative (senna, docusate) when starting opioids. 1
• Increase laxative dose when increasing opioid dose. 1
• Methylnaltrexone 0.15 mg/kg subcutaneously when response to laxatives is insufficient in advanced illness. 1
• Naloxone 1.6 mg subcutaneously daily or methylnaltrexone on alternate days may block dysmotility effects. 1

Systemic Sclerosis or Severe Small Bowel Dysmotility:

• Octreotide 50-100 μg once or twice daily subcutaneously may be dramatically beneficial when other treatments fail, with effect apparent within 48 hours. 1