**Core Concept:** Postural hypotension is a decrease in blood pressure upon assuming a standing position and is commonly observed in patients with autonomic nervous system dysfunction.

**Why the Correct Answer is Right:** The correct answer, Diltiazem, is a calcium channel blocker that reduces calcium influx into vascular smooth muscle cells, leading to vasodilation and a decrease in blood pressure. This mechanism can cause postural hypotension as it impairs the body's ability to maintain blood pressure during the transition from lying to standing.

**Why Each Wrong Option is Incorrect:**

A. Calcium channel blockers (Diltiazem): As mentioned earlier, these drugs cause vasodilation and hypotension.
B. Anticholinergics (Scopolamine): These drugs inhibit cholinergic receptors, leading to decreased heart rate, vasoconstriction, and increased blood pressure. Postural hypotension is less likely with anticholinergics.
C. Beta-blockers (Propranolol): These drugs inhibit catecholamine release and action, which would typically lead to increased blood pressure. Postural hypotension is less likely with beta-blockers.
D. Angiotensin-converting enzyme inhibitors (Enalapril): These drugs increase angiotensin II levels, which would typically lead to increased blood pressure. Postural hypotension is less likely with ACE inhibitors.

**Clinical Pearl:** Postural hypotension is a significant concern in elderly patients as it can lead to falls and fractures. Inform patients on medications that increase the risk of postural hypotension about the symptoms and advise them to gradually change positions to allow their body to adapt to the change in blood pressure.

**Correct Answer:** D. Angiotensin-converting enzyme inhibitors (Enalapril)

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**Core Concept:** Angiotensin-converting enzyme inhibitors (ACE inhibitors) work by inhibiting the conversion of angiotensin I to angiotensin II, which results in decreased vasoconstriction and lower blood pressure.

**Why the Correct Answer is Right:** ACE inhibitors (Enalapril) are less likely to cause postural hypotension due to their mechanism of action. By inhibiting angiotensin II production, they do not contribute to the decrease in blood pressure that causes postural hypotension.

**Why Each Wrong Option is Incorrect:**

A. Calcium channel blockers (Diltiazem) and beta-blockers (Propranolol) cause vasodilation and decreased heart rate, which increases the risk of postural hypotension.
B. Angiotensin II is a potent vasoconstrictor, so inhibiting its production (as with Enalapril) reduces the risk of postural hypotension.
C. Angiotensin II is a potent vasoconstrictor, so blocking its action (e.g., ACE inhibitors) lowers blood pressure and reduces the risk of postural hypotension.

**Clinical Pearls:**

1. Postural hypotension occurs due to the loss of sympathetic tone to the