A patient with hypotension and tachycardia after sildenafil and nitroglycerin interaction is evaluated in the ED. Which is the most likely cause?

• A. Anemia
• B. Hyperthyroidism
• C. Interaction between sildenafil and nitroglycerin
• D. Pulmonary embolism

Answer: (C)

Additive vasodilation from combining sildenafil with nitrates causes a dangerous drop in blood pressure. Sildenafil inhibits PDE-5, which slows the breakdown of cyclic GMP (cGMP). Nitrates increase nitric oxide, which raises cGMP levels. When both are active, cGMP is elevated for longer and to a greater extent, leading to profound systemic vasodilation and hypotension. The tachycardia is a compensatory response to that low blood pressure.

In this ED scenario, the sudden hypotension and tachycardia after receiving both medications strongly point to this interaction as the cause. Anemia or hyperthyroidism wouldn’t explain an abrupt, drug-related drop in BP, and a pulmonary embolism would present with different signs and risk factors and is not specifically linked to this drug combination.