All of the following drugs cause hypeensive crisis in patients with phaeochromocytoma, EXCEPT:
**Core Concept**
Phaeochromocytomas are rare, catecholamine-secreting tumors that can lead to severe hypertension, arrhythmias, and cardiac complications. Certain medications can exacerbate this condition by releasing or stimulating catecholamines.
**Why the Correct Answer is Right**
The correct answer is **C. Nitrates**. Nitrates, such as nitroglycerin, work by releasing nitric oxide, which causes vasodilation and a decrease in blood pressure. However, in patients with phaeochromocytoma, the release of nitric oxide can stimulate the release of catecholamines from the tumor, leading to a severe hypertensive crisis. This is because the nitric oxide can activate guanylyl cyclase, which increases the levels of cyclic guanosine monophosphate (cGMP) in the tumor cells, leading to the release of catecholamines.
**Why Each Wrong Option is Incorrect**
**Option A: Tyramine** is a naturally occurring amine that can cause the release of catecholamines from phaeochromocytomas, leading to a hypertensive crisis.
**Option B: Phentolamine** is a non-selective alpha-adrenergic antagonist that can block the effects of catecholamines, but it can also stimulate the release of catecholamines from phaeochromocytomas, leading to a hypertensive crisis.
**Option D: Sodium nitroprusside** is a potent vasodilator that can cause a rapid decrease in blood pressure, but it can also release cyanide ions, which can stimulate the release of catecholamines from phaeochromocytomas, leading to a hypertensive crisis.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that patients with phaeochromocytoma should avoid certain medications, such as tyramine-containing foods and medications like phentolamine and sodium nitroprusside, which can exacerbate their condition.
**Correct Answer: C. Nitrates**