ラクツロース
**ラクツロース**は、ガラクトースとフルクトースからなる合成二糖類です。獣医療においては、主に以下の2つの重要な役割を果たします： * **肝性脳症（HE）の管理**：肝機能障害（門脈体循環シャント、重度の肝硬変など）の患者において、血中アンモニア濃度を低下させるための基本治療薬です。結腸内でアンモニアを捕捉し、血流への神経毒の蓄積を防ぎます。 * **浸透圧性下剤**：慢性便秘や宿便、特に巨大結腸症を患う猫の管理に広く使用されます。 **臨床のポイント**：猫はラクツロースの粘り気のある甘いシロップを嫌がる傾向があり（流涎や抵抗の原因となります）、結晶製剤（*Kristalose*）をウェットフードに混ぜて与える方が受け入れられやすく、長期的なコンプライアンスが向上することが多いです。
作用機序: 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.
動物種別の用量
- 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
投与経路
禁忌
- 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
有害事象
- 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)
薬物相互作用
- 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
モニタリング
- 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)
過量投与
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.
VetSheet の薬剤リファレンスは、獣医療従事者向けの臨床意思決定支援を目的としており、専門的判断やメーカーの最新添付文書に代わるものではありません。