What is the appropriate dosing and administration of oral polyethylene glycol (PEG) for an elderly, immobile patient with chronic constipation who is taking opioids, anticholinergics, calcium‑channel blockers, and iron?

How to Administer PEG for Elderly, Immobile Patients with Chronic Constipation on Multiple Constipating Medications

Start with PEG 17 grams once daily dissolved in 4-8 ounces of water or other beverage, but first perform a digital rectal examination to rule out fecal impaction—if impaction is present, manual disimpaction must be done before any oral laxative will work. 1, 2

Critical First Step: Rule Out Impaction

• Perform digital rectal examination immediately before starting PEG to detect fecal impaction 1, 2, 3
• If impaction is found, manual disimpaction (digital fragmentation and extraction) is required first, followed by glycerin suppository or isotonic saline enema 1, 2
• Never use sodium phosphate enemas in elderly patients due to serious electrolyte disturbance risks 1, 2
• Only after successful disimpaction should you start oral PEG for maintenance 1, 2

Initial Dosing Protocol

• Start PEG 17 grams once daily mixed in 4-8 ounces of water, juice, or other beverage 1, 2, 4
• This can be taken at any time of day, does not need to be with meals 1, 4
• Goal is one non-forced bowel movement every 1-2 days 1, 2
• Assess response after 3-4 days 2, 3

Dose Escalation if Inadequate Response

• If no response within 3-4 days, increase to PEG 17 grams twice daily (total 34 grams/day in divided doses) 1, 2, 5
• Each dose should be dissolved in 250 mL (approximately 8 ounces) of water 1, 5
• Add stimulant laxative: senna 2 tablets twice daily or bisacodyl 10-15 mg once to three times daily 1, 2, 3
• Reassess after another 3-4 days 2

Critical Safety Warnings for This Patient Population

Absolute Contraindications in This Patient:

• Avoid magnesium hydroxide (Milk of Magnesia) and magnesium citrate entirely due to calcium-channel blocker use and risk of hypermagnesemia, especially with any degree of renal impairment 1, 2, 3
• Avoid bulk-forming laxatives (psyllium, methylcellulose, fiber supplements) because the patient is immobile with likely low fluid intake—these increase mechanical obstruction risk 1, 2, 3
• Avoid liquid paraffin due to immobility and risk of aspiration lipoid pneumonia 1, 2

Monitoring Requirements:

• Monitor for dehydration and electrolyte imbalances given the combination of calcium-channel blockers and osmotic laxatives 1, 2, 3
• Consider checking electrolytes every 2-4 weeks initially if escalating to higher PEG doses 3

If Maximum Oral Therapy Fails

After 1 week of PEG 34 grams daily plus stimulant laxatives without adequate response:

• Add lactulose 30-60 mL twice to four times daily as additional osmotic agent 2
• Consider rectal measures: bisacodyl suppository 10 mg once to twice daily or isotonic saline enema 1, 2
• Re-examine for recurrent impaction or obstruction 2, 3
• Consider peripherally-acting mu-opioid receptor antagonist (methylnaltrexone 0.15 mg/kg subcutaneously every other day) specifically for the opioid-induced component 1

Non-Pharmacological Measures (Essential in Immobile Patients)

• Ensure easy toilet access—this is particularly critical given immobility 1, 2, 3
• Educate to attempt defecation twice daily, 30 minutes after meals, straining no more than 5 minutes 1, 2, 3
• Provide dietetic support and manage decreased food intake which worsens constipation 1, 2
• Increase fluid intake if not contraindicated 1

Evidence for Long-Term Safety

• PEG has demonstrated excellent safety and efficacy for up to 12 months of continuous use in elderly patients 4, 6
• No clinically significant electrolyte disturbances, tachyphylaxis, or serious adverse events were observed in long-term studies 1, 4, 6
• Response is durable over 6 months without loss of effectiveness 1, 6
• Most common side effects are mild: abdominal distension, loose stool, flatulence, nausea 1, 4

Common Pitfall to Avoid

The most critical error is starting oral laxatives without first checking for impaction—oral PEG will not work and may worsen symptoms if a fecal impaction is blocking the colon 1, 2, 3. Always perform digital rectal examination first in elderly, immobile patients on multiple constipating medications.