Gastrointestinal · Year 2 · from Gastrointestinal

Case 2: Opioid-Induced Constipation Management

Patient Demographics

  • Age: 67 years
  • Sex: Female
  • Occupation: Retired teacher

Chief Complaint

"I haven't had a bowel movement in 6 days and my stomach is so bloated."

History of Present Illness

A 67-year-old woman with metastatic breast cancer to bone presents with severe constipation. She was started on extended-release morphine 30 mg twice daily 3 weeks ago for pain control from bony metastases. Since starting opioids, she has had progressively worsening constipation. She previously had daily bowel movements but now has a bowel movement only every 5-7 days despite taking docusate 100 mg twice daily. She describes hard, pellet-like stools requiring significant straining. She has abdominal bloating, cramping, decreased appetite, and nausea. She tried senna but found the cramping intolerable. Her pain is well-controlled on the current morphine dose. She drinks about 4 glasses of water daily and has limited mobility due to bone pain.

Past Medical History

  • Metastatic breast cancer (bone metastases to spine, ribs, pelvis)
  • Hypertension
  • Type 2 diabetes
  • Osteoporosis

Medications

  • Morphine ER 30 mg BID
  • Morphine IR 15 mg PRN breakthrough pain
  • Docusate 100 mg BID
  • Metformin 1000 mg BID
  • Lisinopril 10 mg daily
  • Ondansetron 4 mg PRN nausea

Physical Examination

  • Vital Signs: BP 142/78 mmHg, HR 82 bpm, afebrile
  • General: Thin female, mild distress from abdominal discomfort
  • Abdomen: Distended, tympanitic, diffusely tender, no rebound/guarding; decreased bowel sounds; no palpable masses
  • Rectal: Hard stool in vault, no masses, no blood

Workup

  • Abdominal X-ray: Significant stool burden throughout colon, no obstruction, no free air
  • BMP: Normal (rules out hypercalcemia, hypokalemia)
  • TSH: Normal

Diagnosis

Opioid-Induced Constipation (OIC) - Rome IV criteria met:

  • New or worsening constipation when initiating, changing, or increasing opioid therapy
  • Includes reduced bowel movement frequency, straining, hard stools, sensation of incomplete evacuation

Pathophysiology of OIC

Opioids cause constipation through multiple mechanisms via mu-opioid receptors in the gut:

  1. Decreased peristalsis: Reduced propulsive contractions
  2. Increased water absorption: Prolonged intestinal transit allows more fluid reabsorption
  3. Increased sphincter tone: Reduced relaxation of anal sphincter
  4. Reduced secretions: Decreased fluid secretion into bowel lumen

Unlike most opioid side effects, tolerance to constipation does NOT develop - patients require ongoing bowel management.

Treatment Plan

ACUTE MANAGEMENT (Disimpaction):

  1. Rectal interventions first:
  • Glycerin suppository
  • If ineffective: Bisacodyl suppository
  • Consider mineral oil enema or tap water enema if suppositories fail
  1. Oral osmotic laxative:
  • Polyethylene glycol (MiraLAX) 17 g in 8 oz water once or twice daily until cleared

MAINTENANCE BOWEL REGIMEN:

Step 1: First-Line Agents (Stimulant + Osmotic)

  1. Senna 8.6-17.2 mg at bedtime (stimulant laxative)
  • Works by stimulating colonic motility via myenteric plexus
  • Can start at lower dose and titrate to effect
  1. Polyethylene glycol (PEG) 17 g daily
  • Osmotic laxative - draws water into bowel
  • Adjust dose based on response (can use 17-34 g daily)

Why NOT just docusate?

  • Docusate is a stool softener with minimal evidence of efficacy
  • Does NOT address the reduced motility caused by opioids
  • Should not be used as monotherapy for OIC

Step 2: If Conventional Laxatives Fail - PAMORA Agents

Peripherally Acting Mu-Opioid Receptor Antagonists (PAMORAs):

  • Block mu-opioid receptors in the GI tract
  • Do NOT cross blood-brain barrier - preserve analgesia
  • Do NOT precipitate opioid withdrawal

Options:

  1. Methylnaltrexone (Relistor):
  • Subcutaneous injection 8-12 mg every other day PRN
  • Works within 30-60 minutes
  • Good for acute rescue
  1. Naloxegol (Movantik):
  • Oral, 25 mg daily on empty stomach
  • Avoid with strong CYP3A4 inhibitors
  • First-line oral PAMORA
  1. Naldemedine (Symproic):
  • Oral, 0.2 mg daily
  • Can be taken with or without food

For This Patient:

  • Start senna 8.6 mg BID + PEG 17 g daily
  • If no improvement in 72 hours, add naloxegol 25 mg daily
  • Discontinue ineffective docusate

SUPPORTIVE MEASURES:

  1. Increase fluid intake: Goal 8 glasses daily
  2. Dietary fiber: If tolerated (may worsen bloating in some)
  3. Activity: Encourage mobility as able
  4. Toilet schedule: Attempt bowel movement 30 minutes after meals

IMPORTANT COUNSELING:

  • Start bowel regimen when opioid initiated (prevention > treatment)
  • Take stimulant laxative prophylactically, not PRN
  • OIC will not resolve spontaneously - need ongoing therapy
  • If severe cramping with senna, can switch to different stimulant (bisacodyl) or use osmotic alone

Follow-up

  • Phone follow-up in 3-5 days to assess response
  • Goal: Bowel movement at least every 2-3 days without straining
  • Adjust regimen based on response
  • If PAMORAs needed, continue as long as on opioid therapy

Clinical Pearl

Opioid-induced constipation is the most common opioid side effect and does NOT develop tolerance - it persists throughout opioid therapy. Prevention is key: all patients starting opioids should receive prophylactic bowel regimen (stimulant +/- osmotic laxative). Docusate alone is ineffective for OIC. Conventional laxative failure is common (40-50% of patients), and PAMORAs offer a targeted mechanism-based approach. PAMORAs block peripheral mu-receptors in the gut without affecting central analgesia or causing withdrawal. The ondansetron this patient takes for nausea also has constipating effects (5-HT3 antagonism reduces GI motility) - consider switching to a prokinetic antiemetic if possible.

All cases for this lecture as Markdown