Lactulose, a synthetic sugar, is commonly prescribed as a laxative to treat chronic constipation and to manage hepatic encephalopathy (HE), a complication of severe liver disease. Lactulose is intended to increase bowel movements and soften stool. While an appropriate dose produces soft stools, an excessive dose can easily lead to diarrhea. This effect is directly related to how the medication works within the digestive system.
How Lactulose Works in the Intestines
Lactulose is non-absorbable by the small intestine, traveling largely intact to the large intestine (colon). Once in the colon, it begins a dual-action mechanism. The first effect is osmotic, where the unabsorbed sugar draws water from the body’s tissues into the intestinal tract. This increase in water content softens the stool and significantly increases its volume, stimulating a bowel movement.
The second effect involves gut bacteria in the colon, which ferment the lactulose. This breakdown produces short-chain fatty acids, such as lactic and acetic acids, along with gases. These byproducts further increase osmotic pressure, drawing more water into the bowel.
The resulting acidic environment stimulates peristalsis, the muscle contractions that push stool through the colon. For patients with hepatic encephalopathy, this acidification is important because it traps ammonia, a neurotoxin, which is then expelled with the loose stool.
Distinguishing Normal Loose Stools from Diarrhea
The therapeutic goal for constipation is to produce soft, formed stools, usually two to three times per day. This frequency and softened consistency indicate the medication is working as intended. Mild side effects such as bloating, abdominal cramping, and increased gas are common, especially when first starting the medication.
Diarrhea goes beyond the desired softening and is characterized by overly frequent, watery bowel movements. The difference lies primarily in the wateriness and frequency, rather than just the softness. Problematic diarrhea is defined as an excessive number of loose stools, often more than three to four per day, or any level that interferes with daily life.
While some loose consistency is expected, a sudden onset of frequent, liquid stools signals an over-response to the current dose. This excessive bowel activity can lead to complications such as dehydration and an imbalance of electrolytes. Recognizing this distinction is crucial for patient safety and for determining if a dosage adjustment is necessary.
When to Adjust Dosage or Seek Medical Advice
Frequent, watery diarrhea is a clear sign that the current dose of lactulose is too high. The first action should be to consult the prescribing healthcare provider, who will advise an immediate reduction in the dosage. For many patients, simply cutting the dose in half can bring bowel movements back into the desired range of two to three soft stools daily.
Because frequent loose stools can rapidly deplete the body’s fluid reserves, increasing water and electrolyte intake is important. Drinking extra water or using oral rehydration solutions helps prevent dehydration symptoms like dizziness and fatigue.
Certain symptoms warrant seeking immediate medical attention rather than a simple dose adjustment. These warning signs include indications of severe dehydration, such as extreme thirst, confusion, or reduced urination. Other concerning symptoms are severe, persistent abdominal pain, vomiting, or blood in the stool, which could suggest a more serious gastrointestinal issue. If diarrhea persists despite a dose reduction, the medication may need to be temporarily or permanently discontinued under medical supervision.