In the ED, a patient who takes nitroglycerin for angina and recently took sildenafil develops dizziness and low blood pressure. What is the likely cause?

• A. Overhydration
• B. Interaction between sildenafil and nitroglycerin
• C. Orthostatic hypotension from dehydration
• D. Hypoglycemia

Answer: (B)

Synergistic vasodilation from combining a nitrate with a PDE-5 inhibitor explains the dizziness and low blood pressure. Nitroglycerin releases nitric oxide, which causes smooth muscle relaxation and venous dilation, lowering blood pressure. Sildenafil inhibits phosphodiesterase-5, preventing the breakdown of cGMP and amplifying the nitric oxide–mediated vasodilation. When these drugs are used together, the resulting drop in vascular resistance can be profound, leading to dizziness and hypotension. This is why the most likely cause is the interaction between sildenafil and nitroglycerin. In the ED, stop the nitrate, monitor hemodynamics, place the patient supine, and manage hypotension per protocol; ensure future avoidance of this combination.