Which drug has the highest potential to exacerbate orthostatic hypotension with prazosin?

Labetalol is known to have a higher potential for exacerbating orthostatic hypotension when combined with prazosin due to its mechanisms of action as a non-selective beta-blocker and alpha-1 adrenergic blocker. Prazosin is primarily an alpha-1 blocker used to manage hypertension, and it can lead to a significant drop in blood pressure upon standing, a condition termed orthostatic hypotension.

When labetalol is used concurrently with prazosin, its combined effects can intensify the hypotensive response. Labetalol's alpha-1 blockade can further lower blood pressure, especially in the context of prazosin’s already potent effects on vascular resistance. This synergy can lead to increased risks of dizziness, lightheadedness, or fainting when a patient rises from a sitting or lying position.

The other options, while they are beta-blockers, either do not possess significant alpha-1 blocking activity (like propranolol and atenolol) or have a more balanced profile that alleviates the risk for orthostatic hypotension when compared to labetalol. Thus, it is labetalol that presents the greatest risk of exacerbating orthostatic hypotension when used in conjunction with