What is the recommended dosage of Miralax (polyethylene glycol) for an elderly woman with chronic constipation?

Miralax Dosage for Elderly Woman with 6-Week Constipation

For an elderly woman with 6 weeks of chronic constipation, start with polyethylene glycol (Miralax/PEG) 17 grams once daily dissolved in 4-8 oz of water or other beverage, which is the evidence-based dose specifically validated for elderly patients with an excellent safety profile. 1

Initial Assessment Required

Before starting treatment, you must perform a digital rectal examination to rule out fecal impaction, as this changes the management approach entirely. 2 After 6 weeks of constipation, impaction is highly likely and would require disimpaction first before oral laxatives will be effective.

If No Impaction Present: Standard PEG Dosing

• Start with PEG 17 grams daily (one capful in 4-8 oz of beverage), which produces bowel movements typically within 1-3 days 2, 3
• This dose has been specifically studied in elderly patients with proven long-term safety up to 12 months 4
• PEG is superior to other laxatives in elderly patients due to minimal drug interactions, no electrolyte disturbances, and no risk of aspiration (unlike liquid paraffin) 1
• The goal is one non-forced bowel movement every 1-2 days 1, 2

If Impaction is Present

If digital rectal exam reveals impaction, oral laxatives alone will fail:

• Manual disimpaction is required first - digital fragmentation and extraction of stool, ideally with pre-medication using an analgesic and anxiolytic 1, 2
• Follow with glycerin suppository or isotonic saline enema (NOT phosphate enemas in elderly due to electrolyte risks) 1, 2
• Then start maintenance PEG 17 grams daily to prevent recurrence 2

Dose Escalation if Initial Dose Fails

If PEG 17 grams daily doesn't produce results within 3-4 days:

• Increase to PEG 17 grams twice daily (total 34 grams/day) 1, 2
• Add bisacodyl 10-15 mg daily to three times daily as a stimulant laxative 1, 2
• Consider adding senna 2-3 tablets twice to three times daily 1

Critical Safety Considerations for Elderly Patients

Avoid these common pitfalls:

• Do NOT use magnesium hydroxide (Milk of Magnesia) in elderly patients, especially if any renal impairment exists, due to serious hypermagnesemia risk 1, 5
• Avoid bulk laxatives (psyllium, fiber) if the patient has low fluid intake or is non-ambulatory - these increase obstruction risk 1
• Avoid liquid paraffin if bed-bound or has swallowing difficulties due to aspiration pneumonia risk 1
• Monitor for dehydration and electrolyte imbalances if patient is on diuretics or cardiac glycosides 1

Alternative Agents if PEG Fails

If maximum-dose PEG (34 grams daily) plus stimulant laxatives fail after 1 week:

• Lactulose 30-60 mL twice to four times daily - though this causes more bloating and takes 2-3 days to work 1, 2
• Rectal measures: Bisacodyl suppositories twice daily or isotonic saline enemas 1, 2

Monitoring and Follow-up

• Reassess bowel movement frequency after 3-4 days of treatment 2
• If no improvement after 1 week of escalated therapy, re-examine for impaction or obstruction 1, 2
• Long-term PEG use is safe in elderly patients for up to 12 months without tachyphylaxis 4
• Watch for adverse effects: diarrhea, loose stools, flatulence, nausea (all typically mild) 4

Non-Pharmacological Measures

Implement these concurrently with PEG:

• Ensure easy toilet access, especially if mobility is limited 1
• Encourage attempting defecation twice daily, 30 minutes after meals, straining no more than 5 minutes 1
• Provide dietetic support and manage decreased food intake 1