PEG/Macrogol is Superior to Lactulose for Constipation
Polyethylene glycol (PEG/macrogol) should be your first-line osmotic laxative choice over lactulose for treating constipation in healthy adults, as it demonstrates superior efficacy with better tolerability. 1
What PEG/Macrogol Is
- PEG (polyethylene glycol), also called macrogol, is a high-molecular-weight osmotic laxative that draws water into the intestine to hydrate and soften stool 1
- It is biologically inert, non-absorbable, and causes virtually no net electrolyte disturbance 1, 2
- Available formulations include PEG 3350 and macrogol 4000, both with similar efficacy profiles 2, 3
- PEG can be used with or without added electrolytes—the addition of electrolytes offers no clinical benefit for constipation management 3
Why PEG is Preferred Over Lactulose
The evidence strongly favors PEG over lactulose across multiple outcomes:
- Stool frequency: PEG increases bowel movements more effectively than lactulose 4, 5
- Stool consistency: PEG produces better stool form and requires less straining 4, 5
- Abdominal symptoms: PEG provides superior relief of abdominal pain compared to lactulose 5
- Tolerability: PEG causes significantly less flatulence and bloating than lactulose 2, 4
- Need for rescue therapy: Patients on PEG require fewer additional laxative products 5
Practical Dosing Guidance
For PEG/Macrogol:
- Standard daily dose: 17 g (one sachet) for maintenance therapy 6
- Can titrate to 34 g daily if needed for chronic constipation 6
- For acute relief within 24 hours: 68 g in 500 mL of water provides safe, effective overnight relief without cramping or incontinence 6
- Take with at least 8-10 ounces of fluid 7
For Lactulose (if PEG unavailable):
- Your proposed dose of 30 cc (approximately 20 g) once daily at bedtime is reasonable 1
- However, expect 2-3 day latency before effect and higher likelihood of bloating 1
- Patients typically require higher doses (2+ sachets/day) compared to PEG 4
Clinical Algorithm for Constipation Management
Step 1: Start with oral PEG 1
- Begin with 17 g daily, adjusting based on response
Step 2: Add stimulant laxative if inadequate response after 24-48 hours 1
- Bisacodyl 10-15 mg or senna 8.6-17.2 mg daily 8, 1
- Goal: one non-forced bowel movement every 1-2 days 1
Step 3: If still no response, perform digital rectal exam 1
- Rule out fecal impaction before escalating therapy 1
Step 4: Consider rectal interventions if oral therapy fails 1
Important Clinical Caveats
- Rule out mechanical obstruction before initiating any laxative therapy 1
- Avoid magnesium-based products in patients with renal impairment due to hypermagnesemia risk 8, 1
- Avoid rectal interventions in neutropenic or thrombocytopenic patients 1
- Docusate (stool softeners) should not be used—they lack efficacy evidence and are explicitly not recommended by multiple guidelines 1
- Ensure adequate hydration when using any osmotic laxative to prevent potential complications 7
Bottom Line
Choose PEG 17 g daily over lactulose 30 cc daily—the meta-analysis of 10 randomized controlled trials definitively shows PEG's superiority in both adults and children for stool frequency, consistency, symptom relief, and tolerability 5. Current treatment guidelines from the American Gastroenterological Association and National Comprehensive Cancer Network recommend PEG as the preferred first-line osmotic laxative 1, 2.