**Core Concept**
Hepatic encephalopathy is a neuropsychiatric disturbance caused by liver dysfunction, leading to an accumulation of toxic substances in the blood. The primary mechanism involves the gut-brain axis, where ammonia, a product of nitrogen metabolism, is absorbed from the gut and transferred to the brain via the blood, causing neurotoxicity.

**Why the Correct Answer is Right**
Lactulose is a non-absorbable disaccharide that acts as an osmotic laxative, reducing the absorption of ammonia from the gut. It also produces short-chain fatty acids in the colon, which further increase the pH of the gut lumen, making it less favorable for ammonia production by gut bacteria. This decreases the amount of ammonia absorbed from the gut, thereby reducing its transfer to the brain and alleviating symptoms of hepatic encephalopathy.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Metronidazole is an antibiotic that targets anaerobic bacteria in the gut, but it does not directly address the issue of ammonia production.

**Option B:** This option is incorrect because Loperamide is an opioid receptor agonist that slows gut motility, which can worsen hepatic encephalopathy by allowing more time for ammonia absorption.

**Option C:** This option is incorrect because Rifaximin is an antibiotic that targets Gram-negative bacteria in the gut, but it is not the primary treatment for hepatic encephalopathy.

**Clinical Pearl / High-Yield Fact**
Remember that lactulose is a first-line treatment for hepatic encephalopathy, and its effectiveness is based on its ability to reduce ammonia production and absorption in the gut, making it a crucial component of management.

**Correct Answer: C. Lactulose.**