Cardiovascular drugs: phosphodiesterase 3 inhibitors: 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 · Cardiovascular drugs: phosphodiesterase 3 inhibitors

Sample item

A patient with acute decompensated heart failure on long-term metoprolol responds poorly to dobutamine. Milrinone is added. Which enzyme does milrinone inhibit, and what follows?

ASodium-potassium ATPase, raising intracellular calciumBPhosphodiesterase 5, raising cGMP in pulmonary vesselsCAdenylyl cyclase, lowering cAMP and heart rateDPhosphodiesterase 3, raising cAMP independently of beta receptors

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

The answer and the reasoning

D. Phosphodiesterase 3, raising cAMP independently of beta receptors

Milrinone inhibits phosphodiesterase 3, which prevents breakdown of cAMP in cardiac muscle and vascular smooth muscle. It therefore increases contractility and dilates vessels, acting as an inodilator, and it still works during beta blockade. Hypotension and arrhythmias are the main adverse effects.

Option by option

A. Sodium-potassium ATPase, raising intracellular calcium
Sodium-potassium ATPase inhibition is the action of digoxin.
B. Phosphodiesterase 5, raising cGMP in pulmonary vessels
Phosphodiesterase 5 is the target of sildenafil, not milrinone.
C. Adenylyl cyclase, lowering cAMP and heart rate
Milrinone does not inhibit adenylyl cyclase, and lowering cAMP would reduce contractility.
D. Phosphodiesterase 3, raising cAMP independently of beta receptors (correct)
Correct. Blocking cAMP breakdown gives inotropy and vasodilatation without using beta receptors.

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, Phosphodiesterase 3, raising cAMP independently of beta receptors. Milrinone inhibits phosphodiesterase 3, which prevents breakdown of cAMP in cardiac muscle and vascular smooth muscle.

Why is "Sodium-potassium ATPase, raising intracellular calcium" not the answer?

Sodium-potassium ATPase inhibition is the action of digoxin.

Why is "Phosphodiesterase 5, raising cGMP in pulmonary vessels" not the answer?

Phosphodiesterase 5 is the target of sildenafil, not milrinone.

Why is "Adenylyl cyclase, lowering cAMP and heart rate" not the answer?

Milrinone does not inhibit adenylyl cyclase, and lowering cAMP would reduce contractility.

What concept does this question test?

It tests Cardiovascular drugs: phosphodiesterase 3 inhibitors in Pharmacology. It therefore increases contractility and dilates vessels, acting as an inodilator, and it still works during beta blockade. Hypotension and arrhythmias are the main adverse effects.

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: phosphodiesterase 3 inhibitors?

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.