Lactulose Dosing for Constipation
The recommended dose of lactulose for treating constipation is 10-20 g (15-30 mL) daily, with the option to increase to 40 g (60 mL) daily if needed. 1
Dosing Guidelines
- Initial dose: 10-20 g (15-30 mL) daily
- Maximum dose: Up to 40 g (60 mL) daily if necessary
- Onset of action: 24-48 hours may be required to produce a normal bowel movement
- Administration: Can be taken as a single daily dose or divided into two doses
Mechanism of Action
Lactulose is a synthetic disaccharide that works as an osmotic laxative. It is not digested in the small intestine but exerts its effect in the colon where it:
- Draws water into the intestinal lumen through osmotic action
- Produces a tonic contraction in the colon 2
- Promotes peristalsis and softens stool
Efficacy Considerations
- Lactulose has been shown to significantly increase stool frequency, weight, volume, and water content compared to placebo 3
- The laxative effects appear to be dose-related 3
- In elderly patients, lactulose has demonstrated significant reduction in fecal impactions and need for enemas 4
Practical Administration Tips
- Preparation: For powder formulations, dissolve contents of packet in half a glass (4 ounces) of water 1
- Timing: Can be administered as a single evening dose or divided into two doses with similar efficacy 5
- Titration: Start at the lower end of the dosage range and adjust based on response
- Duration of effect: Effects persist during continued administration, with tolerance improving over time 5
Side Effects and Limitations
- Common side effects: Bloating and flatulence (dose-dependent) are the most common adverse effects 6
- These side effects may limit its use in clinical practice, particularly in patients who already experience abdominal discomfort
- Compared to polyethylene glycol (PEG), lactulose may cause more flatulence, though it remains an effective option 7
Clinical Context
Lactulose can be considered if symptoms of chronic idiopathic constipation have failed to improve with fiber and over-the-counter laxatives 6. It is particularly useful in patients who:
- Do not experience significant bloating or abdominal pain with lactulose use
- Have diabetes mellitus type 2 (as it may not significantly increase blood sugar levels) 6
- Are elderly patients at risk for fecal impaction 4
The overall certainty of evidence for lactulose efficacy is very low according to recent guidelines, but it remains an FDA-approved option for constipation management 6, 1.