What is the protocol for preventing constipation in patients taking narcotics (opioids)?

Prevention of Constipation in Patients Taking Opioids

Start a prophylactic stimulant laxative (senna or bisacodyl) immediately when initiating opioid therapy, as patients do not develop tolerance to opioid-induced constipation and it occurs in up to 80% of patients. 1, 2

Prophylactic Regimen at Opioid Initiation

First-line prophylaxis:

• Senna 2 tablets every morning OR bisacodyl 5-15 mg daily 1, 2
• Adding a stool softener (docusate) to stimulant laxatives is actually less effective than using the stimulant laxative alone, so avoid routine combination therapy 1, 2
• Alternative: Polyethylene glycol (PEG) 17 grams in 8 oz water twice daily 1
• Goal: One non-forced bowel movement every 1-2 days 1, 2

Important considerations:

• Maintain adequate fluid intake 1
• Avoid supplemental fiber (psyllium) - it is ineffective for opioid-induced constipation and may worsen symptoms 1, 2
• Increase laxative dose when increasing opioid dose 2

Escalation for Persistent Constipation

Before escalating therapy, always rule out bowel obstruction or fecal impaction 1, 2

Second-line treatment (if constipation develops despite prophylaxis):

• Increase bisacodyl to 10-15 mg two to three times daily 1, 2
• Add osmotic laxatives: PEG, lactulose, or magnesium-based products (magnesium citrate or magnesium hydroxide) 1
• Consider rectal interventions: bisacodyl suppository 10 mg or glycerin suppository 1, 2
• Consider adding metoclopramide 10-20 mg orally four times daily as a prokinetic agent, though use cautiously due to risk of tardive dyskinesia with chronic use 1, 2

Laxative-Refractory Opioid-Induced Constipation

For patients who fail adequate trials of laxatives, escalate to peripherally-acting μ-opioid receptor antagonists (PAMORAs): 1, 2

PAMORA selection (in order of recommendation strength):

1. Naldemedine 0.2 mg orally once daily - strongest recommendation with high-quality evidence 1, 2
2. Naloxegol 12.5-25 mg orally once daily - strong recommendation with moderate-quality evidence 1, 2
3. Methylnaltrexone 0.15 mg/kg subcutaneously every other day (or 12 mg subcutaneous for weight-based dosing) - conditional recommendation with lower-quality evidence 1, 2

Key advantages of PAMORAs:

• They block opioid receptors in the gut without crossing the blood-brain barrier, so they do not interfere with central pain relief 2
• Effective for rescue therapy when constipation is clearly opioid-related 1

Alternative Strategies

If constipation remains refractory:

• Consider opioid rotation to fentanyl or methadone, which may have less constipating effects 1, 2
• Lubiprostone 24 mcg twice daily (intestinal secretagogue) - though evidence is limited 1

Monitoring

• Use the Bowel Function Index to objectively assess severity (score ≥30 indicates clinically significant constipation) and monitor treatment response 2
• Reassess bowel function regularly and adjust treatment as needed 2

Critical Pitfalls to Avoid

• Never delay prophylactic laxatives - start them with the first opioid dose 2, 3
• Do not use stool softeners alone - they are ineffective without stimulant laxatives 1, 2
• Always rule out obstruction before escalating therapy, especially before adding stimulants or PAMORAs 1, 2
• Avoid bulk-forming laxatives (fiber supplements) as they are ineffective and may worsen symptoms 1, 2