What is the initial treatment for constipation?

Initial Treatment for Constipation

Start with polyethylene glycol (PEG) 17g once daily as first-line pharmacological therapy, combined with increased fluid intake and physical activity when appropriate. 1, 2

First-Line Treatment Approach

The most effective initial management combines:

• Polyethylene glycol (PEG) 17g daily as the preferred osmotic laxative, which generally produces a bowel movement in 1-3 days 1, 2, 3
• Stimulant laxatives (senna or bisacodyl 10-15mg, 2-3 times daily) are equally appropriate as first-line therapy, particularly for opioid-induced constipation 1, 2
• Milk of magnesia 1 oz twice daily is an inexpensive alternative osmotic agent with comparable efficacy 1

All of these first-line agents cost approximately $1 or less per day. 1

Critical Initial Assessment

Before starting treatment, you must rule out:

• Fecal impaction via digital rectal examination 1, 2
• Bowel obstruction 1, 2
• Metabolic causes: hypercalcemia, hypokalemia, hypothyroidism, diabetes mellitus 1, 2
• Medication review: discontinue or adjust constipating medications when feasible 1

A complete blood count is the only laboratory test routinely recommended; metabolic panels (thyroid-stimulating hormone, glucose, calcium) have low diagnostic utility unless other clinical features warrant them. 1

Fiber Supplementation: Important Caveats

Do not rely on fiber as primary therapy for medication-induced constipation. 2, 4

• Fiber (psyllium 15g daily) may be added only if the patient has adequate fluid intake (at least 2 liters daily) 1, 2, 4, 5
• Fiber improves stool frequency and consistency in approximately 50% of patients but causes bloating and flatulence as common side effects 6, 7
• Bulk laxatives like psyllium are specifically not recommended for opioid-induced constipation 1
• Start fiber at low doses with 8-10 ounces of fluid per dose to minimize side effects 4

Stool Softeners: Evidence Against Routine Use

Do not add stool softeners (docusate) to stimulant laxatives. 1, 2, 4

Evidence from the National Comprehensive Cancer Network demonstrates that adding docusate to senna provides no additional benefit. 1, 2

Lifestyle Modifications

While recommended, lifestyle changes alone are insufficient and must be combined with pharmacological therapy:

• Increase fluid intake in patients with low baseline consumption 1, 2, 4
• Increase physical activity within patient limits, though exercise alone has limited efficacy 1, 2, 4
• Establish regular toileting schedules after meals to leverage the gastrocolic reflex 4
• Use a small footstool during defecation to assist gravity and allow easier pressure exertion 4

Treatment Goal

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

If Initial Treatment Fails

When constipation persists despite first-line therapy:

• Add a second laxative: rectal bisacodyl once daily, lactulose, magnesium hydroxide, or magnesium citrate 1, 2
• Caution with magnesium salts: avoid in renal impairment due to risk of hypermagnesemia 1
• Consider suppositories (glycerin or bisacodyl 10-15mg) administered 30 minutes after a meal to synergize with the gastrocolonic response 1

If gastroparesis is suspected, add metoclopramide as a prokinetic agent. 1, 2

For persistent symptoms unresponsive to standard laxatives, consider newer secretagogues (linaclotide, lubiprostone, plecanatide). 1, 2

Special Consideration for Opioid-Induced Constipation

All patients receiving opioid analgesics should be prescribed a concomitant laxative prophylactically unless contraindicated by pre-existing diarrhea. 1, 4

Osmotic or stimulant laxatives are preferred over fiber for opioid-induced constipation. 1, 4