Why is sildenafil or other PDE-5 inhibitor use within the last 24-48 hours a nitroglycerin contraindication?

• A. Because of the risk of severe hypotension when combined with nitrates.
• B. Because nitrates may cause tachycardia and arrhythmias.
• C. Because PDE-5 inhibitors increase bleeding risk with nitrates.
• D. Because nitrates can cause methemoglobinemia with PDE-5 inhibitors.

Answer: (A)

The key idea is that combining a PDE-5 inhibitor with nitrates causes a dangerous drop in blood pressure due to a synergistic increase in nitric oxide–cGMP–mediated vasodilation. Nitrates raise NO, which increases cGMP and relaxes smooth muscle; PDE-5 inhibitors block the breakdown of cGMP, so the vasodilatory effect is amplified. If a PDE-5 inhibitor has been used within the last 24–48 hours, giving nitrates can produce severe hypotension, syncope, or even ischemia, making this a contraindication. The other options don’t address this potent, dose- and time-dependent hemodynamic interaction: they’re not the primary risk when nitrates and PDE-5 inhibitors are combined, and bleeding risk or methemoglobinemia aren’t the central concerns here.