What are the next steps to evaluate and manage a hospitalized patient who remains constipated after receiving an appropriate dose of polyethylene glycol (Miralax) and an enema?

Management of Refractory Constipation After Miralax and Enema Failure

The next step is to perform a digital rectal exam to assess for fecal impaction, and if present, proceed with manual disimpaction followed by combination therapy with a stimulant laxative (bisacodyl 10-15 mg orally 2-3 times daily) added to the existing Miralax regimen. 1

Immediate Assessment

Perform a digital rectal examination (DRE) immediately to determine if fecal impaction is present, as this fundamentally changes management 2, 1. The DRE will identify whether stool is present in the distal rectum versus a proximal impaction (which may present with an empty rectum on exam) 2.

Rule out mechanical bowel obstruction through clinical assessment and imaging if indicated, as stimulant laxatives are contraindicated in obstruction 1. Look for signs of obstruction including severe abdominal distension, absent bowel sounds, or concerning imaging findings 2.

Management Based on DRE Findings

If Fecal Impaction is Present (Distal)

Manual disimpaction is the definitive treatment for distal fecal impaction through digital fragmentation and extraction of stool 2. This should be followed by:

• Glycerin or bisacodyl suppositories to facilitate passage of remaining stool 1
• Water or oil retention enemas after partial disimpaction to soften remaining stool 2
• Resume oral PEG (Miralax) once the distal colon has been partially emptied 2

If Proximal Fecal Impaction is Suspected

When DRE is non-diagnostic but clinical suspicion remains high for proximal impaction 2:

• High-dose PEG lavage with electrolytes (similar to bowel prep solutions) can soften or wash out proximal stool 2
• This requires absence of complete bowel obstruction 2
• Consider doses of 68-85g of PEG for more rapid effect within 24 hours 3

If No Impaction is Present

Add bisacodyl 10-15 mg orally 2-3 times daily to the existing Miralax regimen 1. This combination is critical because:

• Osmotic laxatives (Miralax) and stimulant laxatives work synergistically through different mechanisms 1
• Bisacodyl directly stimulates colonic motility, addressing pathophysiology that osmotic agents alone cannot overcome 1
• The American Gastroenterological Association provides strong recommendation with moderate-quality evidence for this approach 1

Lactulose 30-60 mL daily can be added if constipation persists despite bisacodyl, though bloating and flatulence are dose-dependent side effects 1.

Advanced Therapies if Refractory

If the patient fails combination therapy with PEG and bisacodyl 1:

• Lubiprostone or linaclotide are recommended by the American Gastroenterological Association for chronic constipation unresponsive to over-the-counter therapies 1
• Prucalopride (a 5-HT4 agonist) directly stimulates colonic motility and is superior for chronic constipation 1
• Peripheral opioid antagonists (methylnaltrexone or naloxegol) if the patient is on opioids 2

Critical Pitfalls to Avoid

Do not continue magnesium-based laxatives long-term due to risk of hypermagnesemia, especially with any degree of renal impairment 2, 1.

Do not add more fiber for refractory constipation, as fiber is unlikely to control established constipation and may worsen symptoms in non-ambulatory patients with low fluid intake 2, 1.

Avoid enemas in specific contraindications including neutropenia (WBC < 0.5 cells/μL), thrombocytopenia, paralytic ileus, recent colorectal surgery, severe colitis, or recent pelvic radiotherapy 2.

Do not use metoclopramide routinely as a next step; it should only be used when gastroparesis is documented or strongly suspected 1.

Maintenance After Resolution

Implement a maintenance bowel regimen to prevent recurrence once disimpaction is achieved 2. This typically involves continuing combination therapy with osmotic and stimulant laxatives at lower maintenance doses 2, 1.