Neurology: phenytoin toxicity: practice question

A General Medicine 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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General Medicine · Neurology: phenytoin toxicity

Sample item

A patient on phenytoin has nystagmus, ataxia and slurred speech. Which long-term adverse effect is characteristic of this drug?

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

The answer and the reasoning

D. Gingival hyperplasia and hirsutism

Phenytoin has zero-order saturable kinetics, so small dose increases cause toxicity (nystagmus, ataxia). Chronic effects include gingival hyperplasia, hirsutism, coarse facies, megaloblastic anaemia and osteomalacia. Hyponatraemia and aplastic anaemia relate to carbamazepine.

Option by option

  • A. Weight loss and kidney stones

    Weight loss and stones suggest topiramate.

  • B. Hyponatraemia and aplastic anaemia

    These are carbamazepine effects.

  • C. Pancreatitis and hair thinning

    Pancreatitis and hair loss suggest valproate.

  • D. Gingival hyperplasia and hirsutism (correct)

    Correct. These are classic chronic phenytoin effects.

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 General Medicine question

What is the answer to this General Medicine question?

The best answer is D, Gingival hyperplasia and hirsutism. Phenytoin has zero-order saturable kinetics, so small dose increases cause toxicity (nystagmus, ataxia).

Why is "Weight loss and kidney stones" not the answer?

Weight loss and stones suggest topiramate.

Why is "Hyponatraemia and aplastic anaemia" not the answer?

These are carbamazepine effects.

Why is "Pancreatitis and hair thinning" not the answer?

Pancreatitis and hair loss suggest valproate.

What concept does this question test?

It tests Neurology: phenytoin toxicity in General Medicine. Chronic effects include gingival hyperplasia, hirsutism, coarse facies, megaloblastic anaemia and osteomalacia. Hyponatraemia and aplastic anaemia relate to carbamazepine.

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 Neurology: phenytoin toxicity?

For each disease know the classic presentation, the best test, and the first-line treatment. Then use the flashcards and the other General Medicine 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.