Lactulose Contraindications
Lactulose is contraindicated in patients who require a low galactose diet, as it contains galactose (less than 1.6 g per 15 mL). 1
Absolute Contraindication
- Galactosemia or low galactose diet requirement: This is the only FDA-labeled absolute contraindication for lactulose, as the medication contains galactose as a component of its molecular structure 1
Clinical Situations Requiring Extreme Caution (Relative Contraindications)
While not formally listed as absolute contraindications, the following conditions warrant extreme caution or avoidance based on guideline evidence:
Intestinal Obstruction and Perforation
- Intestinal perforation or obstruction: Although this contraindication is specifically mentioned for prucalopride in the guidelines 2, the same principle applies to lactulose given its osmotic mechanism that increases intestinal fluid and gas production
- Lactulose's mechanism of drawing water into the intestinal lumen could worsen obstruction or lead to perforation in compromised bowel 3, 4
Inflammatory Bowel Disease (Active/Severe)
- Toxic megacolon or severe inflammatory bowel disease: Similar to prucalopride's contraindications 2, lactulose should be avoided in toxic megacolon given the risk of colonic distension from gas production during bacterial fermentation 3, 4
Important Clinical Precautions (Not Absolute Contraindications)
Electrolyte Disturbances
- Risk of hypokalemia and hypernatremia: Excessive dosing can lead to diarrhea with potential complications including hypokalemia (low potassium) and hypernatremia (high sodium) from fluid and electrolyte losses 3, 4
- Patients at highest risk include those on diuretics, elderly patients with reduced renal potassium conservation, and those receiving high-dose lactulose for hepatic encephalopathy 3
- Monitor baseline and follow-up potassium levels, especially when titrating to higher doses 3
Pregnancy Considerations
- First trimester pregnancy: Lactulose should be administered with caution in the first trimester, though it remains the only osmotic agent studied in pregnancy and is actually preferred in pregnant patients with constipation 3, 5
Diabetes Mellitus
- Lactulose contains small amounts of galactose and lactose, which may affect blood glucose control, though it is still recommended as first-line osmotic therapy for diabetic constipation 5
Common Pitfalls to Avoid
- Excessive dosing leading to dehydration: The most common error is not titrating the dose appropriately, leading to excessive diarrhea and subsequent electrolyte disturbances 3, 6
- Start at 10-20 g (15-30 mL) daily and titrate based on response, with a maximum of 40 g (60 mL) daily for constipation 3, 5
- Ignoring galactosemia: Always screen for galactosemia or galactose-restricted diets before prescribing, as this is the only absolute FDA contraindication 1