What is the recommended dosing for Duphalac (lactulose) in the treatment of Irritable Bowel Syndrome with Constipation (IBS-C)?

Duphalac (Lactulose) Dosing for IBS-C

Polyethylene glycol (PEG) is recommended over lactulose for IBS-C, as lactulose is not specifically recommended in current guidelines for IBS-C treatment. 1

First-Line Treatment Options for IBS-C

• Soluble fiber (ispaghula/psyllium) is recommended as a first-line treatment at 3-4 g/day initially, gradually increasing to an optimal dose of 20 g/day to avoid bloating 1, 2
• Polyethylene glycol (PEG) may be an effective treatment for constipation in IBS, though abdominal pain is a common side effect 1
• Certain antispasmodics may be effective for global symptoms and abdominal pain in IBS-C 1

Lactulose Use in IBS-C

While lactulose (Duphalac) is not specifically recommended in current guidelines for IBS-C, if considering its use:

• Standard lactulose dosing is 15 g daily as an osmotic laxative 1
• Titration should be based on symptom response and side effects 1
• No clear maximum dose is established in guidelines 1

Important Considerations for Lactulose

• Bloating and flatulence are common side effects that may limit tolerability, especially in IBS patients who already experience these symptoms 1
• Lactulose is the only osmotic agent extensively studied in pregnancy 1
• Lactulose may have a persistent "carry-over" effect compared to stimulant laxatives 3

Second-Line Treatments for IBS-C

If first-line treatments fail, the following second-line options should be considered:

• Linaclotide (290 μg once daily) is strongly recommended as the most efficacious secretagogue for IBS-C, though diarrhea is a common side effect 1
• Lubiprostone (8 μg twice daily) is recommended for IBS-C and may cause less diarrhea than other secretagogues, but nausea is a frequent side effect 1
• Plecanatide (3 mg daily) is another effective option for IBS-C 1
• Tenapanor (50 mg twice daily) is effective for IBS-C but may not be available in many countries 1

Treatment Algorithm

1. Start with soluble fiber (ispaghula) at 3-4 g/day, gradually increasing to 20 g/day 1, 2
2. If inadequate response, consider PEG as an osmotic laxative 1
3. If lactulose is chosen (though not preferred), start at 15 g daily and titrate based on response 1
4. For patients with persistent symptoms, escalate to second-line agents such as linaclotide, lubiprostone, plecanatide, or tenapanor 1
5. Consider tricyclic antidepressants as gut-brain neuromodulators for global symptoms and abdominal pain 1

Common Pitfalls

• Lactulose often causes bloating and flatulence, which may worsen existing IBS symptoms 1
• Inadequate fiber dosing - most patients don't reach the optimal 20 g/day dose needed for symptom improvement 2
• Failure to explain the rationale for treatments, which may reduce adherence 4
• Not allowing sufficient time for treatments to work - improvement may take several weeks 5