Antimicrobials: cotrimoxazole: 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 · Antimicrobials: cotrimoxazole

Sample item

Consider a newborn whose mother took cotrimoxazole close to term, and an elderly man on cotrimoxazole and ramipril develops weakness. Which adverse effects fit each case?

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

The answer and the reasoning

C. Kernicterus risk from bilirubin displacement in the neonate, and hyperkalaemia in the elderly man

Sulfonamides displace bilirubin from albumin, risking kernicterus near term, and trimethoprim blocks ENaC like amiloride, causing hyperkalaemia, particularly with ACE inhibitors. Sequential blockade of folate synthesis and reduction gives synergy.

Option by option

  • A. Gingival hyperplasia and hyperglycaemia

    Gingival hyperplasia is a phenytoin effect.

  • B. Ototoxicity and hypomagnesaemia

    Ototoxicity is typical of aminoglycosides.

  • C. Kernicterus risk from bilirubin displacement in the neonate, and hyperkalaemia in the elderly man (correct)

    Correct. Both effects are documented.

  • D. Grey baby syndrome and hypokalaemia

    Grey baby syndrome belongs to chloramphenicol, and trimethoprim causes hyperkalaemia.

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.

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Questions about this Pharmacology question

What is the answer to this Pharmacology question?

The best answer is C, Kernicterus risk from bilirubin displacement in the neonate, and hyperkalaemia in the elderly man. Sulfonamides displace bilirubin from albumin, risking kernicterus near term, and trimethoprim blocks ENaC like amiloride, causing hyperkalaemia, particularly with ACE inhibitors.

Why is "Gingival hyperplasia and hyperglycaemia" not the answer?

Gingival hyperplasia is a phenytoin effect.

Why is "Ototoxicity and hypomagnesaemia" not the answer?

Ototoxicity is typical of aminoglycosides.

Why is "Grey baby syndrome and hypokalaemia" not the answer?

Grey baby syndrome belongs to chloramphenicol, and trimethoprim causes hyperkalaemia.

What concept does this question test?

It tests Antimicrobials: cotrimoxazole in Pharmacology. Sequential blockade of folate synthesis and reduction gives synergy.

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 Antimicrobials: cotrimoxazole?

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.