Lactulose
**Lactulose** is a synthetic disaccharide derivative of lactose, composed of galactose and fructose. In veterinary medicine, it serves two primary, highly effective roles: * **Hepatic Encephalopathy (HE) Management**: It is a cornerstone therapy for reducing blood ammonia levels in patients with compromised liver function (e.g., portosystemic shunts, severe cirrhosis). By trapping ammonia in the colon, it prevents neurotoxic accumulation in the bloodstream. * **Osmotic Laxative**: It is widely used to manage chronic constipation and obstipation, particularly in cats suffering from megacolon. **Clinical Pearl**: Because cats often despise the sticky, sweet syrup form of lactulose (which can lead to hypersalivation and resistance), the crystal formulation (*Kristalose*) mixed into wet food is often much better tolerated and improves long-term compliance.
กลไกการออกฤทธิ์: Lactulose exerts its effects locally in the gastrointestinal tract through two distinct mechanisms: * **Ammonia Reduction (Ion Trapping)**: Lactulose is not hydrolyzed by mammalian gut enzymes. It reaches the colon intact, where it is fermented by resident bacteria into low-molecular-weight organic acids (**lactic, formic, and acetic acids**). This fermentation drops the colonic pH. The acidic environment causes diffusible, neurotoxic ammonia (**NH3**) to migrate from the bloodstream into the colon, where it is protonated into the non-diffusible ammonium ion (**NH4+**). The ammonium is then trapped in the lumen and excreted in the feces. * **Osmotic Laxative Effect**: The unabsorbed disaccharide and its organic acid metabolites exert a strong osmotic pressure, drawing water into the bowel lumen. This increases fecal bulk and moisture, stimulating colonic peristalsis and facilitating bowel movements.
ขนาดยาตามชนิดสัตว์
- Hepatic encephalopathy · 0.25-1 mL · PO · As needed · Individualize dosage until semi-formed stools are produced
- Constipation · 1/2 to 3/4 of a teaspoonful · PO · twice daily · Suggested dose
- Constipation · 5-10 mL per cat · Rectal · Once · Administered slowly as an enema with a well-lubricated 10-12 (french) rubber catheter or feeding tube
- Constipation · 0.5 mL/kg · PO · two to three times a day
- Chronic constipation (maintaining soft stools) · 0.5 mL/kg · PO · two to three times daily · Dosage is adjusted to obtain the stool quality desired
- Hepatic encephalopathy / Constipation · Dose not specified in text. Titrate to effect (reduce dose if diarrhoea develops). · PO · Not specified · Ongoing · Alternative provided in text: Lactitol (β-galactosidosorbitol) powder at 500 mg/kg/day divided in 3 or 4 doses, adjusted to produce 2 or 3 soft stools per day.
- Hepatic encephalopathy; to stimulate appetite, improve intestinal flora · 0.03 mL (Cockatiel); 0.1 mL (Amazon) · PO · two to three times a day · May be used for weeks · Reduce dosage if diarrhea develops
- Laxative · 0.3 mL/kg · PO · q12h · Green Iguana
วิธีการให้ยา
ข้อห้ามใช้
- Patients requiring a low-galactose diet
- Use with caution in diabetic patients (contains free lactose and galactose)
- Use with caution in patients with preexisting fluid and electrolyte imbalances
- Severely encephalopathic animals at risk of inhalation/aspiration
- Gastrointestinal obstruction
- Animals at risk of gastrointestinal perforation
อาการไม่พึงประสงค์
- Flatulence
- Gastric distention
- Abdominal cramping
- Diarrhea (dose-dependent)
- Dehydration (secondary to excessive diarrhea)
- Hypersalivation/aversion in cats (due to taste/texture)
- Diarrhoea
- Dehydration (with excessive dosing)
อันตรกิริยาระหว่างยา
- Oral Antacids · Non-adsorbable antacids may reduce the colonic acidification effects and overall efficacy of lactulose. · moderate
- Other Laxatives · Should not be used concurrently; loose stools may be falsely attributed to lactulose, resulting in inadequate dosing for hepatic encephalopathy. · moderate
- Neomycin (and other oral antibiotics) · Theoretically, oral antibiotics could eliminate the colonic bacteria required to metabolize lactulose, reducing its efficacy. However, clinical synergy is often observed when treating hepatic encephalopathy. Enhanced monitoring is recommended.
- Oral antibiotics (e.g., neomycin) · Synergy may occur when used together for hepatic encephalopathy. · minor
- Insulin · Lactulose syrup contains free lactose and galactose, which may alter insulin requirements in diabetic patients. · moderate
- 5-aminosalicylic acid (and other pH-dependent colon-release drugs) · Can be inactivated because lactulose decreases the pH of the colon. · major
การติดตาม
- Clinical efficacy: Aim for 2-3 soft, semi-formed stools per day when used for hepatic encephalopathy or constipation.
- Hydration status.
- Serum electrolytes (especially during long-term use or in patients with preexisting fluid/electrolyte abnormalities).
- Faecal consistency (aim for 2-3 soft, formed stools per day)
- Blood ammonia levels (in hepatic encephalopathy)
- Hydration status and electrolytes
- Blood glucose levels (in diabetic patients)
การได้รับยาเกินขนาด
Excessive doses of lactulose may cause **flatulence, severe diarrhea, abdominal cramping, and dehydration**. **Management**: * Reduce the dosage or temporarily discontinue the medication. * Provide supportive care, including **replacement of fluids and electrolytes** if dehydration or imbalances occur.
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