**Question:** Nitroprusside active metabolite acts by:

**Core Concept:** Nitroprusside is a vasodilator drug used to reduce blood pressure. It is converted to a nitric oxide (NO) analog, sodium nitroprusside (SNP), which is responsible for its pharmacological effects.

**Why the Correct Answer is Right:** Nitroprusside is a nitric oxide (NO) donor drug, which means it releases NO upon conversion to its active form, sodium nitroprusside (SNP). SNP is a nitric oxide analog that mimics the effects of nitric oxide, a potent vasodilator. SNP activates soluble guanylate cyclase (sGC) in the smooth muscle cells of blood vessels, causing an increase in cyclic guanosine monophosphate (cGMP) levels. This leads to vasodilation and a decrease in blood pressure.

**Why Each Wrong Option is Incorrect:**

A. SNP does not act via calcium channel blockers, as it is a nitric oxide analog, not a calcium channel modulator.
B. SNP does not act as a COX inhibitor, as it does not target cyclooxygenase enzymes.
C. SNP does not act as a direct vasodilator like sodium nitroglycerin, as it is a nitric oxide analog.
D. SNP does not act as a direct vasodilator like hydralazine, as it is a nitric oxide analog, not a direct vasodilator.

**Correct Answer:** SNP (sodium nitroprusside) acts as a nitric oxide analog, which is responsible for its vasodilatory effects.