Tadalafil can potentiate the hypotensive effect of GTN. Which option lists this as the correct drug?

• A. Salbutamol
• B. Levothyroxine
• C. Tadalafil
• D. Fluconazole

Answer: (C)

The key idea is a dangerous interaction between nitrates and PDE-5 inhibitors. Tadalafil is a PDE-5 inhibitor used for erectile dysfunction. Nitrates like GTN release nitric oxide, which increases the smooth muscle level of cGMP and causes vasodilation and a drop in blood pressure. When a PDE-5 inhibitor like tadalafil is taken with a nitrate, it blocks the breakdown of cGMP, amplifying this vasodilatory effect and can lead to severe hypotension, fainting, or even heart problems. Because of this, tadalafil is the drug whose interaction with GTN is classic and clinically important.

The other options don’t have this specific, well-known interaction with nitrates: salbutamol is a bronchodilator with different cardiovascular effects, levothyroxine has no direct nitrate interaction, and fluconazole is an antifungal that can affect drug levels but does not describe the same direct potentiation of nitrate-induced hypotension as seen with PDE-5 inhibitors like tadalafil.