A. Nitrates can be used 24 hours after sildenafil
B. Nitrates are safe to use simultaneously with sildenafil
C. Nitrates can be used 12 hours after sildenafil
D. NItrates are safe to use simultaneously with sildenafil as long as an alpha blocker is not also being used
Phosphodiesterase inhibitors (sildenafil, vardenafil, tadalafil) used to treat erectile dysfunction enhance nitric oxide production and can cause potentially fatal hypotension when used in combination of nitrates. These two drugs should not be used together within 24 hours (sildenafil) or 48 hours (vardenafil, tadalafil) due to this interaction. Alpha blockers cause significant hypotension as well and caution is advised while using an alpha blocker with a phosphodiesterase inhibitor. Interesting, phosphodiesterase inhibitors were initially being investigated for the treatment of stable angina when researchers noted the improvement of erectile dysfunction and thus redirected their efforts.