Respiratory drugs: theophylline 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 · Respiratory drugs: theophylline interactions

Sample item

A 55-year-old man with COPD stable on theophylline is given ciprofloxacin for a urinary infection and soon develops tremor, vomiting and a seizure. What explains this?

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

The answer and the reasoning

B. Ciprofloxacin inhibits CYP1A2, raising theophylline concentration to toxic levels

Theophylline has a narrow therapeutic range and is metabolised by CYP1A2. Ciprofloxacin, erythromycin and cimetidine inhibit its metabolism, and toxicity presents with nausea, tachyarrhythmia and seizures, whereas smoking and rifampicin lower levels.

Option by option

  • A. Theophylline inhibits ciprofloxacin excretion

    The interaction runs the other way round.

  • B. Ciprofloxacin inhibits CYP1A2, raising theophylline concentration to toxic levels (correct)

    Correct. CYP1A2 inhibition caused theophylline toxicity.

  • C. Ciprofloxacin induces CYP1A2

    Induction would lower the levels.

  • D. Direct bronchospasm from the antibiotic

    Bronchospasm does not explain seizures.

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, Ciprofloxacin inhibits CYP1A2, raising theophylline concentration to toxic levels. Theophylline has a narrow therapeutic range and is metabolised by CYP1A2.

Why is "Theophylline inhibits ciprofloxacin excretion" not the answer?

The interaction runs the other way round.

Why is "Ciprofloxacin induces CYP1A2" not the answer?

Induction would lower the levels.

Why is "Direct bronchospasm from the antibiotic" not the answer?

Bronchospasm does not explain seizures.

What concept does this question test?

It tests Respiratory drugs: theophylline interactions in Pharmacology. Ciprofloxacin, erythromycin and cimetidine inhibit its metabolism, and toxicity presents with nausea, tachyarrhythmia and seizures, whereas smoking and rifampicin lower levels.

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 Respiratory drugs: theophylline 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.