General pharmacology and pharmacokinetics: enzyme inhibition onset: 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 · General pharmacology and pharmacokinetics: enzyme inhibition onset

Sample item

A man on stable doses of theophylline for asthma starts cimetidine for dyspepsia and within two days develops tremor, palpitations and vomiting with a high theophylline level. What is the mechanism?

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

The answer and the reasoning

A. Inhibition of hepatic microsomal metabolism

Cimetidine binds the haem iron of several cytochrome P450 enzymes, including CYP1A2, and slows theophylline metabolism. Inhibition begins within days, whereas induction takes one to two weeks to develop.

Option by option

  • A. Inhibition of hepatic microsomal metabolism (correct)

    Correct. Cimetidine inhibits CYP enzymes, so theophylline accumulates quickly.

  • B. Increased gastric absorption due to less acid

    Reduced acid does not enhance theophylline absorption to this degree.

  • C. Enhanced reabsorption in the renal tubule

    Tubular reabsorption does not change with cimetidine in a way that raises theophylline.

  • D. Displacement from albumin binding sites

    Theophylline is only moderately protein bound, and displacement would not raise free drug for long.

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 A, Inhibition of hepatic microsomal metabolism. Cimetidine binds the haem iron of several cytochrome P450 enzymes, including CYP1A2, and slows theophylline metabolism.

Why is "Increased gastric absorption due to less acid" not the answer?

Reduced acid does not enhance theophylline absorption to this degree.

Why is "Enhanced reabsorption in the renal tubule" not the answer?

Tubular reabsorption does not change with cimetidine in a way that raises theophylline.

Why is "Displacement from albumin binding sites" not the answer?

Theophylline is only moderately protein bound, and displacement would not raise free drug for long.

What concept does this question test?

It tests General pharmacology and pharmacokinetics: enzyme inhibition onset in Pharmacology. Inhibition begins within days, whereas induction takes one to two weeks to develop.

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 General pharmacology and pharmacokinetics: enzyme inhibition onset?

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.