一位 55 歲末期失代償性肝硬化男性出現意識模糊、定向力差、雙手前伸時撲翼樣震顫（asterixis）。實驗室顯示血氨大幅升高，符合肝性腦病變。醫師開立口服或直腸 lactulose。Lactulose 在此情境的藥理機轉為何？
A 55-year-old male with end-stage decompensated cirrhosis presents with confusion, disorientation, and asterixis (flapping tremor) when extending his hands. Labs show severely elevated ammonia, consistent with hepatic encephalopathy. The provider orders oral or rectal lactulose. What is the pharmacologic mechanism of lactulose in this condition?
- AIt binds to red blood cells to deliver oxygen to paralyzed muscles.它與紅血球結合以將氧氣輸送至麻痺的肌肉。
- BIt acidifies the colon, trapping ammonia as ammonium and excreting it via increased bowel movements.✓ 正解它使結腸酸化，將氨截留為銨離子並通過增加排便將其排出。
- CIt serves as a brain-energy syrup that fuels malnourished neurons with glucose.它作為大腦能量糖漿，以葡萄糖為營養不良的神經元提供燃料。
- DIt shrinks the enlarged liver to normal size to restore venous flow.它使腫大的肝臟縮小到正常大小以恢復靜脈血流。
肝性腦病變（hepatic encephalopathy）由肝臟無法解氨導致血氨入腦引起。 選項 B 正確：Lactulose 在腸道被細菌代謝產生酸（lactic acid、acetic acid），降低腸道 pH。在酸性環境下，氨（NH3）轉為帶電的銨離子（NH4+），無法穿過腸黏膜被吸收，且 lactulose 滲透性瀉劑作用增加排便，將氨排出體外。 選項 D 錯誤：lactulose 不影響肝臟大小。 選項 C 錯誤：lactulose 不被吸收為能量。 選項 A 錯誤：與紅血球無關。
Hepatic encephalopathy is caused by ammonia accumulation due to liver failure to convert it to urea. C correct: Lactulose is metabolized by colonic bacteria to acids (lactic, acetic), lowering bowel pH. The acidic environment converts ammonia (NH3) to ammonium (NH4+), which cannot be absorbed across the bowel wall. Lactulose's osmotic laxative effect increases stool output, eliminating ammonia. A incorrect: Lactulose does not affect liver size. B incorrect: Lactulose is not absorbed as fuel. D incorrect: Unrelated to RBCs.
世界急重症腸胃科國考必背方程式！「肝硬化 (Liver cirrhosis) = 毒氣氨無法被代謝 (Ammonia high) 衝擊大腦 = 意識模糊與手顫抖撲翼 (Asterixis)。解法唯一指定：灌入超級糖漿 Lactulose 拼命腹瀉把氨拉出來」。無地緣差別。