Nucleotide metabolism: febuxostat versus allopurinol: 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: febuxostat versus allopurinol

Sample item

A patient with gout develops a severe hypersensitivity rash to allopurinol. His physician prescribes febuxostat. Which property of febuxostat distinguishes it from allopurinol?

AIt blocks renal reabsorption of urateBIt is a recombinant enzyme that degrades uric acidCIt inhibits hypoxanthine-guanine phosphoribosyltransferaseDIt is a non-purine selective inhibitor of xanthine oxidase

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

The answer and the reasoning

D. It is a non-purine selective inhibitor of xanthine oxidase

Febuxostat is a non-purine, selective inhibitor of xanthine oxidase, so it does not resemble hypoxanthine and does not interfere with other purine and pyrimidine enzymes. It is metabolised mainly in the liver, so it can be used in mild renal impairment. Allopurinol, a purine analogue, is converted to oxypurinol.

Option by option

A. It blocks renal reabsorption of urate
Blocking renal urate reabsorption is the action of uricosurics such as probenecid.
B. It is a recombinant enzyme that degrades uric acid
A recombinant enzyme that degrades uric acid is rasburicase, given intravenously.
C. It inhibits hypoxanthine-guanine phosphoribosyltransferase
Inhibiting HGPRT would block salvage and increase purine synthesis, worsening hyperuricaemia.
D. It is a non-purine selective inhibitor of xanthine oxidase (correct)
Correct. Its non-purine structure allows selective inhibition of the same target enzyme.

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 D, It is a non-purine selective inhibitor of xanthine oxidase. Febuxostat is a non-purine, selective inhibitor of xanthine oxidase, so it does not resemble hypoxanthine and does not interfere with other purine and pyrimidine enzymes.

Why is "It blocks renal reabsorption of urate" not the answer?

Blocking renal urate reabsorption is the action of uricosurics such as probenecid.

Why is "It is a recombinant enzyme that degrades uric acid" not the answer?

A recombinant enzyme that degrades uric acid is rasburicase, given intravenously.

Why is "It inhibits hypoxanthine-guanine phosphoribosyltransferase" not the answer?

Inhibiting HGPRT would block salvage and increase purine synthesis, worsening hyperuricaemia.

What concept does this question test?

It tests Nucleotide metabolism: febuxostat versus allopurinol in Biochemistry. It is metabolised mainly in the liver, so it can be used in mild renal impairment. Allopurinol, a purine analogue, is converted to oxypurinol.

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: febuxostat versus allopurinol?

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.