What is the recommended treatment approach for constipation management, including lifestyle modifications and medication doses, in patients with varying ages, medical histories, and current medications?

Constipation Management with Dosing

For chronic idiopathic constipation, start with polyethylene glycol (PEG) 17g once daily as first-line pharmacological therapy, combined with lifestyle modifications including 2 liters of fluid daily. 1, 2

Initial Assessment

Before initiating treatment, perform these critical evaluations:

• Digital rectal examination to rule out fecal impaction 2
• Clinical assessment to exclude bowel obstruction 1, 2
• Medication review for constipating agents 2
• Complete blood count (the only routinely recommended laboratory test) 2

First-Line Pharmacological Treatment: Polyethylene Glycol (PEG)

PEG is the preferred initial agent with strong evidence supporting its use:

• Starting dose: 17g (one heaping tablespoon) mixed in 8 ounces of liquid once daily 1, 2
• Can be mixed in water, juice, soda, coffee, or tea 2
• Take with food to minimize nausea 1
• Titrate up to twice daily (17g BID) if inadequate response 1, 2
• No clear maximum dose 1
• Efficacy: Increases complete spontaneous bowel movements by 2.9 per week and spontaneous bowel movements by 2.3 per week compared to placebo 1, 2
• Response is durable over 6 months 1, 2
• Common side effects: abdominal distension, loose stool, flatulence, nausea 1, 2

Essential Lifestyle Modifications (Concurrent with PEG)

Fluid intake:

• Minimum 2 liters daily, especially if baseline intake is low 2
• Critical when using fiber supplements to prevent worsening or obstruction 2

Dietary fiber:

• Target: 14g fiber per 1,000 kcal intake 1
• May consider fiber supplements (psyllium, methylcellulose, polycarbophil) for mild constipation 2, 3
• Increase slowly over several weeks to minimize bloating and flatulence 3
• Best evidence exists for psyllium, though quality is low 1

Physical activity:

• Encourage regular exercise and early mobilization within patient limits 2

Second-Line Options (If PEG Inadequate)

Add to or replace PEG with:

• Lactulose: 15g daily, titrate per response 1, 2

  • Only osmotic agent studied in pregnancy 1
  • Bloating and flatulence may limit use at higher doses 1

• Magnesium oxide: 400-500mg daily 1

  • Prior studies used 1,000-1,500mg daily 1
  • Use with caution in renal insufficiency and pregnancy 1

• Magnesium citrate or magnesium hydroxide: 30-60mL daily 1, 2

• Bisacodyl: 5mg daily, maximum 10mg daily 1

  • Recommended for short-term use or rescue therapy 1
  • Side effects include cramping and abdominal discomfort 1
  • Long-term safety and efficacy unknown 1

• Senna: 8.6-17.2mg daily 1

  • Recommended maximum is 4 tablets twice daily 1
  • Long-term safety and efficacy unknown 1

Third-Line Options (Refractory Cases)

Secretagogues:

• Lubiprostone: 24mcg twice daily with food and water 1, 4

  • Intestinal secretagogue acting on chloride channel type 2 1, 4
  • May benefit abdominal pain 1
  • Swallow capsules whole; do not break apart or chew 4
  • Common adverse reactions: nausea, diarrhea, headache, abdominal pain 4
  • Contraindicated in mechanical gastrointestinal obstruction 4

• Linaclotide (consider trial if symptoms do not improve) 3

Prokinetic agents:

• Metoclopramide: 10-20mg PO 3-4 times daily (if gastroparesis suspected) 1, 2

Treatment Goal

Achieve one non-forced bowel movement every 1-2 days 1, 2

Special Populations

Opioid-induced constipation:

• Prophylactic regimen: Stimulant laxative (senna) + stool softener (docusate), 2 tablets every morning; maximum 8-12 tablets per day 1
• Increase laxative dose when increasing opioid dose 1
• If refractory: Consider methylnaltrexone 0.15mg/kg subcutaneously 1
• Lubiprostone 24mcg twice daily is FDA-approved for opioid-induced constipation in chronic non-cancer pain 4
  • Effectiveness not established for diphenylheptane opioids (e.g., methadone) 4

Parkinson's disease:

• Fermented milk containing probiotics and prebiotic fiber in addition to increased water and fiber intake 1

Advanced cancer:

• Preferred options: osmotic laxatives (PEG, lactulose, magnesium salts) or stimulant laxatives (senna, bisacodyl, sodium picosulfate) 1

Elderly patients:

• Same treatment algorithm as younger adults, but pay particular attention to living situation, comorbidities, and complete medication list 1, 3

Critical Pitfalls to Avoid

• Do NOT use stool softeners (docusate) alone or add them to stimulant laxatives (except in opioid-induced constipation) 2
• Do NOT rely on fiber supplements for medication-induced constipation 2
• Do NOT increase fiber without ensuring adequate fluid intake (minimum 2L daily) 2
• Avoid long-term use of magnesium-based laxatives due to potential toxicity, especially in renal insufficiency 1, 3
• Compounds like Metamucil are unlikely to control opioid-induced constipation and are not recommended 1

Management of Fecal Impaction

If impaction is present:

• Disimpaction through digital fragmentation and extraction 1
• Followed by enemas (Fleet, saline, or tap water) 1
• Then implement maintenance bowel regimen to prevent recurrence 1
• In absence of suspected perforation or bleed 1