PEG 3350 Treatment Protocol for IBS-C
Start with PEG 3350 17 g once daily mixed in 8 ounces of liquid, continue for at least 2 weeks to assess response, and titrate upward based on symptom relief and tolerability—this regimen increases complete spontaneous bowel movements by approximately 3 per week and provides durable efficacy for up to 6 months. 1
Initial Dosing and Administration
Begin with 17 g of PEG 3350 once daily, dissolved in a minimum of 4 ounces but preferably 8 ounces of any beverage (water, juice, soda, coffee, or tea). 1, 2
Ensure adequate fluid intake throughout the day beyond just the mixing liquid—insufficient hydration is a common cause of treatment failure. 2, 3
Allow 2–4 days for initial bowel movement to occur, with optimal therapeutic effect typically achieved after 1–2 weeks of consistent dosing. 2
Expected Clinical Outcomes
PEG 3350 increases complete spontaneous bowel movements by 2.9 per week compared to placebo. 1, 2
It increases total spontaneous bowel movements by 2.3 per week versus placebo. 1, 2
312 additional patients per 1,000 achieve responder criteria (≥3 spontaneous bowel movements per week) compared to placebo. 1, 2
454 additional patients per 1,000 report global symptom relief. 1, 2
Dose Titration Algorithm
If inadequate response after 2 weeks of 17 g daily with confirmed adequate fluid intake, increase the dose (e.g., to 34 g daily or higher). 1, 2
No definitive maximum dose exists—titrate based on individual response and tolerability. 1, 2
Studies have used doses ranging from 17 g to 85 g daily, with higher doses (68 g) providing relief within 24 hours in some patients. 4
Managing Inadequate Response
If no bowel movement occurs after 3–4 days of optimal PEG therapy with adequate hydration, add a stimulant laxative such as senna (8.6–17.2 mg daily) or bisacodyl (5–10 mg daily). 2, 3
This combination exploits complementary mechanisms: PEG provides osmotic stool softening while stimulant laxatives enhance colonic motility. 2, 3
Consider adding a bisacodyl suppository (10 mg) or glycerin suppository if oral combination therapy fails by day 3–4, while continuing oral PEG. 3
Long-Term Maintenance
Continue PEG 3350 as maintenance therapy once constipation resolves—therapeutic response is durable for up to 6 months and has been studied for up to 52 weeks. 1, 2, 5
Approximately 61.7% of patients may require additional laxative interventions within 30 days of stopping PEG, supporting the need for continued maintenance in many patients. 2, 6
Monthly laboratory monitoring over 6 months shows no clinically significant changes in electrolytes, calcium, glucose, BUN, creatinine, or serum osmolality. 2
Safety Profile and Side Effects
Common adverse effects include abdominal distension, bloating, cramping, flatulence, and nausea—these are typically mild to moderate. 1, 2
Diarrhea occurs in 158 additional patients per 1,000 compared to placebo. 1, 2
All adverse events are consistent with expected laxative effects and rarely lead to discontinuation. 1, 2
Common Pitfalls to Avoid
Do not assume PEG failure without confirming the patient is using the full 17 g dose mixed in at least 8 ounces of liquid and maintaining adequate daily fluid intake. 2, 3
Do not delay adding a stimulant laxative beyond 3–4 days of optimal PEG therapy without response, as the risk of fecal impaction increases. 3
Do not add fiber supplements when PEG fails—fiber is ineffective for established constipation and may worsen bloating. 3
Rule out bowel obstruction or fecal impaction before escalating therapy or adding rectal interventions. 3
Combination with Other IBS-C Therapies
PEG 3350 can be combined with linaclotide (Constella) or other secretagogues, as they work through different mechanisms (osmotic versus guanylate cyclase-C activation). 7
When using combination therapy, start with standard dosing of each agent (PEG 17 g daily + linaclotide at its approved dose) and monitor for excessive loose stools. 7
For severe IBS-C or patients who have failed multiple single-agent therapies, combination therapy may be particularly beneficial. 7