How to manage constipation in patients on methadone (opioid agonist) therapy?

Management of Constipation in Patients on Methadone Therapy

Prophylactic treatment with stimulant laxatives and stool softeners should be initiated immediately when starting methadone therapy, as constipation is the most common and persistent opioid side effect that does not improve over time. 1

Preventive Measures (First-Line Approach)

• Prophylactic medications:

  • Stimulant laxative + stool softener combination (e.g., senna-docusate, 2 tablets every morning; maximum 8-12 tablets per day) 1
  • Increase laxative dose when increasing methadone dose 1

• Lifestyle modifications:

  • Maintain adequate fluid intake
  • Encourage physical activity when feasible
  • Maintain adequate dietary fiber intake (note: fiber supplements like Metamucil alone are unlikely to control methadone-induced constipation) 1

When Constipation Develops (Step-Up Approach)

Step 1: Assessment

• Assess for cause and severity of constipation
• Rule out bowel obstruction
• Check for other treatable causes (hypercalcemia, hypokalemia, hypothyroidism, diabetes mellitus) 1

Step 2: Initial Management

• Titrate stool softener/laxative combination with goal of one non-forced bowel movement every 1-2 days 1
• If impaction is present, administer glycerin suppositories or perform manual disimpaction 1

Step 3: For Persistent Constipation

• Add bisacodyl 10-15 mg, 2-3 times daily 1
• Consider adding another agent:
  • Magnesium hydroxide (30-60 mL daily)
  • Bisacodyl suppository daily
  • Lactulose (30-60 mL daily)
  • Sorbitol (30 mL every 2 hours × 3, then as needed)
  • Magnesium citrate
  • Polyethylene glycol (capful in 8 oz water daily) 1
• Consider Fleet, saline, or tap water enema 1
• If gastroparesis is suspected, add metoclopramide (10-20 mg PO three times daily) 1

Step 4: Refractory Constipation

• Consider methylnaltrexone 0.15 mg/kg subcutaneously every other day (maximum once daily) for constipation that hasn't responded to standard laxative therapy 1
  • Contraindicated in patients with bowel obstruction or postoperative ileus 1
  • Shown to effectively reverse methadone-induced constipation without affecting analgesia or causing withdrawal symptoms 2, 3

Important Clinical Considerations

• Unlike other opioid side effects, constipation generally does not improve over time and requires ongoing management 1
• Patients on methadone maintenance therapy are particularly susceptible to constipation and may require aggressive prophylactic treatment 2
• Regular assessment of bowel function is essential - aim for bowel movements every 1-2 days 1
• Consider opioid rotation if constipation remains intractable despite multiple interventions 1
• Avoid bulk-forming laxatives alone (e.g., Metamucil) as they are typically insufficient for opioid-induced constipation 1

Common Pitfalls to Avoid

1. Waiting for constipation to develop rather than initiating prophylactic treatment
2. Failing to increase laxative doses when methadone doses are increased
3. Relying solely on increased fluid intake and dietary modifications
4. Not recognizing that constipation is the most common reason patients abandon opioid therapy 4
5. Overlooking the need for regular reassessment of bowel function
6. Delaying use of peripherally-acting μ-opioid receptor antagonists like methylnaltrexone in refractory cases

By following this algorithmic approach to managing methadone-induced constipation, clinicians can significantly reduce patient discomfort and improve treatment adherence.