Nucleotide metabolism: probenecid mechanism: practice question

A Biochemistry 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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Biochemistry · Nucleotide metabolism: probenecid mechanism

Sample item

A man with recurrent gout attacks has a normal 24-hour urinary uric acid excretion, indicating renal underexcretion. He is started on probenecid. How does it lower serum urate?

AIt blocks tubular reabsorption of urate through URAT1BIt blocks synthesis of PRPPCIt inhibits the enzyme xanthine oxidaseDIt breaks down urate into allantoin

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

The answer and the reasoning

A. It blocks tubular reabsorption of urate through URAT1

Probenecid inhibits the organic anion transporter URAT1 in the proximal tubule, reducing urate reabsorption and increasing its excretion. It suits underexcretors with good renal function. Fluids are advised to reduce the risk of uric acid stones, and it is ineffective in advanced renal impairment.

Option by option

A. It blocks tubular reabsorption of urate through URAT1 (correct)
Correct. Uricosuric drugs block renal tubular urate reabsorption.
B. It blocks synthesis of PRPP
PRPP synthesis is not the target of any standard gout drug.
C. It inhibits the enzyme xanthine oxidase
Xanthine oxidase is inhibited by allopurinol and febuxostat, which reduce production.
D. It breaks down urate into allantoin
Conversion of urate to allantoin is the action of rasburicase, a recombinant uricase.

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 Biochemistry question

What is the answer to this Biochemistry question?

The best answer is A, It blocks tubular reabsorption of urate through URAT1. Probenecid inhibits the organic anion transporter URAT1 in the proximal tubule, reducing urate reabsorption and increasing its excretion.

Why is "It blocks synthesis of PRPP" not the answer?

PRPP synthesis is not the target of any standard gout drug.

Why is "It inhibits the enzyme xanthine oxidase" not the answer?

Xanthine oxidase is inhibited by allopurinol and febuxostat, which reduce production.

Why is "It breaks down urate into allantoin" not the answer?

Conversion of urate to allantoin is the action of rasburicase, a recombinant uricase.

What concept does this question test?

It tests Nucleotide metabolism: probenecid mechanism in Biochemistry. It suits underexcretors with good renal function. Fluids are advised to reduce the risk of uric acid stones, and it is ineffective in advanced renal impairment.

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 Nucleotide metabolism: probenecid mechanism?

Build one table of enzyme deficiency, disease, inheritance and key finding, then revise it by spaced recall. Then use the flashcards and the other Biochemistry 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.