Drug interactions: 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 · Drug interactions

Sample item

A woman using an oral contraceptive pill is started on rifampicin for tuberculosis. Why is the contraceptive likely to fail?

ARifampicin inhibits hepatic enzymes, raising hormone levelsBRifampicin blocks absorption of the hormones from the gutCRifampicin displaces the hormones from plasma proteinsDRifampicin induces hepatic enzymes, increasing metabolism of the hormones

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

The answer and the reasoning

D. Rifampicin induces hepatic enzymes, increasing metabolism of the hormones

Rifampicin is a potent inducer of CYP enzymes, particularly CYP3A4, and so speeds the metabolism of oestrogen and progestin. Plasma hormone levels fall, ovulation may escape and an additional or alternative contraceptive method is advised.

Option by option

A. Rifampicin inhibits hepatic enzymes, raising hormone levels
Rifampicin is an enzyme inducer, not an inhibitor, so hormone levels fall rather than rise.
B. Rifampicin blocks absorption of the hormones from the gut
Rifampicin does not block intestinal absorption of contraceptive steroids.
C. Rifampicin displaces the hormones from plasma proteins
Protein-binding displacement is not the mechanism and would at most cause a transient change.
D. Rifampicin induces hepatic enzymes, increasing metabolism of the hormones (correct)
Correct. Enzyme induction lowers hormone concentrations and can cause contraceptive failure.

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 Pharmacology question

What is the answer to this Pharmacology question?

The best answer is D, Rifampicin induces hepatic enzymes, increasing metabolism of the hormones. Rifampicin is a potent inducer of CYP enzymes, particularly CYP3A4, and so speeds the metabolism of oestrogen and progestin.

Why is "Rifampicin inhibits hepatic enzymes, raising hormone levels" not the answer?

Rifampicin is an enzyme inducer, not an inhibitor, so hormone levels fall rather than rise.

Why is "Rifampicin blocks absorption of the hormones from the gut" not the answer?

Rifampicin does not block intestinal absorption of contraceptive steroids.

Why is "Rifampicin displaces the hormones from plasma proteins" not the answer?

Protein-binding displacement is not the mechanism and would at most cause a transient change.

What concept does this question test?

It tests Drug interactions in Pharmacology. Plasma hormone levels fall, ovulation may escape and an additional or alternative contraceptive method is advised.

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 Drug interactions?

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.