Cardiovascular drugs: nitrate and sildenafil interaction: 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.

Try it

Pharmacology · Cardiovascular drugs: nitrate and sildenafil interaction

Sample item

A 60-year-old man on isosorbide mononitrate for angina takes a friend's sildenafil tablet. Within an hour he collapses with a blood pressure of 70/40 mmHg. What is the mechanism of this reaction?

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

The answer and the reasoning

D. Additive rise in vascular smooth muscle cGMP causing profound vasodilation

Nitrates release nitric oxide, which activates guanylyl cyclase and raises cGMP. Sildenafil inhibits phosphodiesterase-5, the enzyme that degrades cGMP, so the two together cause excessive and prolonged vasodilation. This combination is contraindicated, and the nitrate must be avoided for at least 24 hours after sildenafil.

Option by option

  • A. Methaemoglobinaemia from the nitrate, aggravated by sildenafil

    Methaemoglobinaemia occurs only with very high nitrite exposure and does not explain an acute drop in blood pressure within an hour.

  • B. Beta-1 receptor blockade by sildenafil causing bradycardic shock

    Sildenafil has no beta-blocking action; hypotension here is from vasodilation, not bradycardia.

  • C. Blockade of L-type calcium channels in the myocardium by sildenafil

    Sildenafil acts on PDE-5, not on calcium channels; calcium channel blockers such as verapamil act there.

  • D. Additive rise in vascular smooth muscle cGMP causing profound vasodilation (correct)

    Correct. Increased synthesis plus reduced breakdown of cGMP produces exaggerated vasodilation.

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.

More Pharmacology questions

Questions about this Pharmacology question

What is the answer to this Pharmacology question?

The best answer is D, Additive rise in vascular smooth muscle cGMP causing profound vasodilation. Nitrates release nitric oxide, which activates guanylyl cyclase and raises cGMP.

Why is "Methaemoglobinaemia from the nitrate, aggravated by sildenafil" not the answer?

Methaemoglobinaemia occurs only with very high nitrite exposure and does not explain an acute drop in blood pressure within an hour.

Why is "Beta-1 receptor blockade by sildenafil causing bradycardic shock" not the answer?

Sildenafil has no beta-blocking action; hypotension here is from vasodilation, not bradycardia.

Why is "Blockade of L-type calcium channels in the myocardium by sildenafil" not the answer?

Sildenafil acts on PDE-5, not on calcium channels; calcium channel blockers such as verapamil act there.

What concept does this question test?

It tests Cardiovascular drugs: nitrate and sildenafil interaction in Pharmacology. Sildenafil inhibits phosphodiesterase-5, the enzyme that degrades cGMP, so the two together cause excessive and prolonged vasodilation. This combination is contraindicated, and the nitrate must be avoided for at least 24 hours after sildenafil.

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 Cardiovascular drugs: nitrate and sildenafil interaction?

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.