Sildenafil citrate, a drug used to treat erectile dysfunction (ED), is marketed under the name Filagra. Men of all ages are susceptible to ED, a prevalent disorder. The inability to achieve or sustain an erection that is sufficiently firm for sexual activity is its defining feature. Filagra is an inhibitor of phosphodiesterase type 5 (PDE5). An enzyme called PDE5 degrades cGMP, a substance that...