What is the recommended treatment for constipation using Movicol (polyethylene glycol 3350) and lactulose?

Movicol (PEG 3350) vs Lactulose for Constipation

Polyethylene glycol 3350 (Movicol) should be used preferentially over lactulose for treating chronic constipation, as it demonstrates superior efficacy with fewer side effects. 1, 2

Evidence Supporting PEG 3350 Superiority

Efficacy Outcomes

• PEG 3350 produces significantly more bowel movements per week compared to lactulose (7.9 vs 5.7 movements per week in pediatric studies) 3
• PEG 3350 improves stool consistency more effectively than lactulose, with better scores on the Bristol Stool Form Scale 1
• PEG 3350 provides superior relief of abdominal pain and reduces the need for additional laxative products 1
• Colonic transit time is significantly faster with PEG 3350 (47.6 hours vs 55.3 hours with lactulose) 4

Tolerability Profile

• PEG 3350 causes significantly fewer side effects than lactulose, particularly less bloating, flatulence, and abdominal pain 1, 3
• Lactulose commonly causes dose-dependent bloating and flatulence which limit its clinical use 5
• PEG 3350 produces less flatus compared to lactulose 2

Mechanism of Action

PEG 3350 (Movicol)

• Works as a non-absorbable, non-metabolized osmotic agent that retains water in the stool to soften it and increase bowel movement frequency 6
• Does not undergo colonic fermentation, which explains the reduced gas and bloating 6

Lactulose

• Functions as a synthetic disaccharide that is not digested in the small intestine and exerts osmotic effects in the colon 5
• Undergoes colonic fermentation, which accelerates ascending colon emptying but produces significant gas as a byproduct 7

Dosing Recommendations

PEG 3350 (Movicol)

• Standard adult dose: 17 grams (one heaping tablespoon) dissolved in 4-8 oz of water, juice, or other beverage daily 6
• First bowel movement typically occurs within 2-4 days 6
• Intended for 1-2 week courses initially, though longer use may be appropriate under physician guidance 6

Lactulose

• FDA-approved dose: 10-20 grams (15-30 mL) daily, may increase to 40 grams (60 mL) daily if needed 5
• Alternative dosing: 30-60 mL twice to four times daily for refractory cases 8

Clinical Application Algorithm

First-Line Approach

1. Start with PEG 3350 17 grams daily as the preferred osmotic laxative 1, 2
2. Adjust dose between 1-3 sachets daily based on response 2
3. Continue for 1-2 weeks to achieve optimal results 6

When to Consider Lactulose

• Reserve lactulose for patients who have failed fiber and OTC laxatives and do not experience significant bloating with its use 5
• Consider lactulose in elderly nursing home patients where it has shown particular benefit in reducing fecal impactions 5
• Lactulose may be appropriate in diabetic patients (non-insulin dependent type 2) as it may not significantly increase blood sugar 5

Escalation Strategy

• If PEG 3350 alone is insufficient, add bisacodyl 10-15 mg daily to three times daily 8
• For opioid-induced constipation refractory to osmotic laxatives, escalate to peripheral opioid antagonists (naldemedine, naloxegol, or methylnaltrexone) 5, 8
• Magnesium-based laxatives (magnesium hydroxide 30-60 mL daily-BID) can be added, but use cautiously in renal impairment 8

Important Caveats

Contraindications and Precautions

• Do not use PEG 3350 in patients with bowel obstruction symptoms (nausea, vomiting, abdominal pain or distention) 6
• Discontinue if allergic reaction occurs (hives, skin rashes) 6
• Lactulose should be avoided in patients who cannot tolerate bloating or flatulence, as these are very common side effects 5

Common Pitfalls

• Taking more than the prescribed PEG dose may cause severe diarrhea and fluid loss 6
• Both agents work similarly in opioid-induced constipation, though PEG remains slightly more effective 5
• The evidence for lactulose is of very low quality (based on old trials from 40+ years ago with small sample sizes), whereas PEG has more robust modern evidence 5