What substance may increase hypotension when taken with doxazosin?

The correct choice, sildenafil, can lead to increased hypotension when taken with doxazosin because both substances have vasodilatory effects. Doxazosin is an alpha-1 adrenergic blocker commonly used to treat hypertension and benign prostatic hyperplasia, resulting in relaxation of vascular smooth muscle and a subsequent reduction in blood pressure. Sildenafil, primarily used for erectile dysfunction, enhances blood flow by inhibiting phosphodiesterase type 5 (PDE5), leading to vasodilation as well.

When these two medications are combined, they can potentiate each other's effects, increasing the risk of hypotension due to the additive vasodilatory action. This means that the hypotensive effect may be more significant than when each drug is taken alone. Consequently, patients using both doxazosin and sildenafil should be monitored closely for symptoms of low blood pressure to avoid complications.