When is nitroglycerin contraindicated?

• A. Low blood pressure or PDE5 inhibitors
• B. High blood pressure
• C. Normal blood pressure
• D. Dehydration

Answer: (A)

Nitroglycerin lowers blood pressure by dilating veins and arteries through increased nitric oxide and cGMP in smooth muscle. Because of this, it is dangerous when blood pressure is already low, since it can drop further and cause inadequate perfusion or fainting. It is also strongly contraindicated with PDE5 inhibitors (like sildenafil, tadalafil, vardenafil) because both drugs raise cGMP and markedly enhance vasodilation, leading to severe hypotension and potential major complications.

So the best answer highlights situations where nitroglycerin should not be used: when blood pressure is low, or when a PDE5 inhibitor is being used. High blood pressure or normal blood pressure do not by themselves contraindicate nitroglycerin, and dehydration is not an absolute contraindication, though dehydration with hypotension would warrant caution and management of the hypotension first.