Autonomic nervous system: lactulose in hepatic encephalopathy: practice question

A Pharmacology question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Pharmacology · Autonomic nervous system: lactulose in hepatic encephalopathy

Sample item

A man with cirrhosis becomes drowsy and confused with asterixis after a gastrointestinal bleed. A non-absorbable disaccharide is started to lower his blood ammonia. How does it act?

AColonic bacteria turn it into acids that trap ammonia as ammonium and speed transitBIt inhibits the intestinal enzyme that forms ammonia from dietary proteinCIt supplies substrates that drive the hepatic urea cycleDIt increases renal excretion of ammonia

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

A. Colonic bacteria turn it into acids that trap ammonia as ammonium and speed transit

Lactulose is fermented by colonic bacteria to organic acids. The acid lumen converts diffusible NH3 to non-absorbable NH4+, and the osmotic effect and bacterial growth increase stool output. Rifaximin lowers the number of ammonia-producing bacteria, and ornithine aspartate feeds the urea cycle.

Option by option

A. Colonic bacteria turn it into acids that trap ammonia as ammonium and speed transit (correct)
Correct. Acidification traps ammonia as ammonium and the laxative effect clears it.
B. It inhibits the intestinal enzyme that forms ammonia from dietary protein
Reducing urease-producing bacteria is the effect attributed to rifaximin or neomycin, and not to lactulose.
C. It supplies substrates that drive the hepatic urea cycle
Providing urea cycle substrates is the proposed action of L-ornithine L-aspartate.
D. It increases renal excretion of ammonia
Lactulose acts in the colon and does not act on the kidney.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

Questions about this Pharmacology question

What is the answer to this Pharmacology question?

The best answer is A, Colonic bacteria turn it into acids that trap ammonia as ammonium and speed transit. Lactulose is fermented by colonic bacteria to organic acids.

Why is "It inhibits the intestinal enzyme that forms ammonia from dietary pro…" not the answer?

Reducing urease-producing bacteria is the effect attributed to rifaximin or neomycin, and not to lactulose.

Why is "It supplies substrates that drive the hepatic urea cycle" not the answer?

Providing urea cycle substrates is the proposed action of L-ornithine L-aspartate.

Why is "It increases renal excretion of ammonia" not the answer?

Lactulose acts in the colon and does not act on the kidney.

What concept does this question test?

It tests Autonomic nervous system: lactulose in hepatic encephalopathy in Pharmacology. The acid lumen converts diffusible NH3 to non-absorbable NH4+, and the osmotic effect and bacterial growth increase stool output. Rifaximin lowers the number of ammonia-producing bacteria, and ornithine aspartate feeds the urea cycle.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Autonomic nervous system: lactulose in hepatic encephalopathy?

Learn drugs as classes, then the exception in each class that an examiner would pick. Then use the flashcards and the other Pharmacology questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.