Drugs in pregnancy: enzyme inducers and neonatal bleeding: 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 · Drugs in pregnancy: enzyme inducers and neonatal bleeding

Sample item

A newborn of a mother who took phenytoin throughout pregnancy bleeds from the umbilical stump and gut on the first day. The prothrombin time is prolonged with a normal platelet count. What is the mechanism?

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

The answer and the reasoning

B. Enzyme induction causing vitamin K deficiency and low factors II, VII, IX and X

Enzyme-inducing antiepileptics such as phenytoin, phenobarbitone and carbamazepine increase vitamin K catabolism and reduce its transfer to the fetus. The newborn develops early haemorrhagic disease with low vitamin K-dependent factors, so vitamin K is given to the baby at birth.

Option by option

  • A. Direct suppression of fetal bone marrow

    Marrow suppression would lower platelets as well, which are normal here.

  • B. Enzyme induction causing vitamin K deficiency and low factors II, VII, IX and X (correct)

    Correct. Induction depletes vitamin K and the dependent clotting factors.

  • C. Antibody-mediated destruction of fetal platelets

    A normal platelet count excludes antibody-mediated thrombocytopenia.

  • D. Inhibition of fibrinogen synthesis by the fetal liver

    Fibrinogen synthesis is not the problem; the prolonged prothrombin time reflects the vitamin K-dependent factors.

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 B, Enzyme induction causing vitamin K deficiency and low factors II, VII, IX and X. Enzyme-inducing antiepileptics such as phenytoin, phenobarbitone and carbamazepine increase vitamin K catabolism and reduce its transfer to the fetus.

Why is "Direct suppression of fetal bone marrow" not the answer?

Marrow suppression would lower platelets as well, which are normal here.

Why is "Antibody-mediated destruction of fetal platelets" not the answer?

A normal platelet count excludes antibody-mediated thrombocytopenia.

Why is "Inhibition of fibrinogen synthesis by the fetal liver" not the answer?

Fibrinogen synthesis is not the problem; the prolonged prothrombin time reflects the vitamin K-dependent factors.

What concept does this question test?

It tests Drugs in pregnancy: enzyme inducers and neonatal bleeding in Pharmacology. The newborn develops early haemorrhagic disease with low vitamin K-dependent factors, so vitamin K is given to the baby at birth.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. 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 Drugs in pregnancy: enzyme inducers and neonatal bleeding?

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.