What is the treatment algorithm for constipation?

Treatment Algorithm for 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, 2

Step 1: Initial Assessment and Rule Out Secondary Causes

Before initiating treatment, perform a digital rectal examination to assess for fecal impaction or obstruction 1. Rule out metabolic causes including:

• Hypercalcemia
• Hypokalemia
• Hypothyroidism
• Diabetes mellitus 1, 2

Discontinue medications that may cause constipation (anticholinergics, antacids, antiemetics) 1. In the absence of alarm features (blood in stool, anemia, weight loss), only a complete blood count is necessary—metabolic panels and colonoscopy are not routinely recommended 1.

Step 2: First-Line Pharmacologic Treatment

Initiate a stimulant laxative immediately rather than starting with lifestyle modifications alone 1, 2:

• Bisacodyl 10-15 mg, 2-3 times daily OR
• Senna at equivalent dosing 1, 2

Critical pitfall to avoid: Do NOT add stool softeners (docusate) to stimulant laxatives—evidence shows no additional benefit 2. This is a common mistake in clinical practice.

Step 3: Add Lifestyle Modifications Concurrently

While starting pharmacologic therapy, implement:

• Increased fluid intake (at least 2 liters daily if using fiber) 1, 3
• Increased physical activity within patient limits 1
• Privacy and comfort for defecation 1
• Positioning aids (small footstool to assist gravity) 1
• Scheduled toileting 30 minutes after meals to synergize with gastrocolonic response 1

Regarding fiber: Gradually increase dietary fiber intake, but understand that supplemental medicinal fiber (psyllium) is unlikely to control medication-induced constipation and may worsen symptoms without adequate fluid intake 4, 2. Fiber works in only 50% of patients and requires weeks to titrate 5.

Step 4: Second-Line Treatment for Persistent Constipation

If constipation persists after 1-2 weeks, add an osmotic laxative 1, 2:

• Polyethylene glycol (PEG) 17g daily (preferred, approximately $1/day) 1
• Lactulose 1
• Magnesium hydroxide (milk of magnesia) 1 oz twice daily 1
• Magnesium citrate 1

Caution: Magnesium-based laxatives should be used cautiously in renal impairment due to risk of hypermagnesemia 1, 6. Avoid long-term use 6.

Alternatively, add rectal bisacodyl suppositories (preferably 30 minutes after meals) or glycerin suppositories 1.

Step 5: Manage Fecal Impaction if Present

If digital rectal examination identifies a full rectum or fecal impaction 1:

• Glycerin suppositories 1
• Manual disimpaction (digital fragmentation and extraction) 1
• Enemas (sodium phosphate, saline, or tap water) 1, 4

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.

Step 6: Consider Prokinetic Agents if Gastroparesis Suspected

If gastroparesis is suspected (particularly relevant with GLP-1 agonist use), add 1, 2:

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

Step 7: Newer Agents for Refractory Constipation

When symptoms do not respond to standard laxatives, consider newer agents (daily cost $7-9) 1:

• Linaclotide 1, 2, 7
• Lubiprostone 1, 2, 7
• Prucalopride (not available in the United States but approved elsewhere) 1, 7, 8

Special Considerations

Opioid-Induced Constipation

• All patients on opioids should receive prophylactic laxatives (stimulant or osmotic) unless contraindicated by pre-existing diarrhea 1
• Avoid bulk laxatives (psyllium) for opioid-induced constipation 1
• Combined opioid/naloxone medications reduce risk of opioid-induced constipation 1
• For unresolved opioid-induced constipation, consider methylnaltrexone 0.15 mg/kg every other day (peripherally acting mu-opioid receptor antagonist) 1, 6

Elderly Patients

• PEG 17g/day offers efficacy with good safety profile 1
• Avoid liquid paraffin in bed-bound patients or those with swallowing disorders (aspiration risk) 1
• Avoid non-absorbable fiber/bulk agents in non-ambulatory patients with low fluid intake (mechanical obstruction risk) 1
• Monitor for dehydration and electrolyte imbalances if on concurrent diuretics or cardiac glycosides 1
• If swallowing difficulties present, rectal measures (enemas/suppositories) may be preferred 1

Cancer/Palliative Care Patients

• Abdominal massage can reduce gastrointestinal symptoms, particularly with concomitant neurogenic problems 1
• Osmotic laxatives (PEG, lactulose) or stimulant laxatives (senna, bisacodyl, sodium picosulfate) are preferred 1

Step 8: Specialized Testing for Non-Responders

If symptoms persist despite the above measures, perform anorectal testing to evaluate for defecatory disorders 1:

• Anorectal manometry
• Balloon expulsion test
• Defecography 1

If anorectal tests are normal or symptoms persist despite treatment of defecatory disorder, evaluate colonic transit time 1.

Step 9: Biofeedback for Defecatory Disorders

Pelvic floor retraining by biofeedback therapy is recommended over laxatives for defecatory disorders, with success rates exceeding 70% 1. This involves training patients to relax pelvic floor muscles during straining and restore normal coordination 1.

Step 10: Surgical Options (Last Resort)

For well-documented slow-transit constipation resistant to aggressive, prolonged medical therapy 1:

• Total colectomy with ileorectal anastomosis may be considered after excluding coexistent upper GI motility disorders, defecatory disorders, and psychological disorders 1, 8

Treatment Goal: Aim for one non-forced bowel movement every 1-2 days, not necessarily daily bowel movements 1, 2.