Pharmacology of phosphodiesterase 5 inhibitors.

The phosphodiesterase enzymes, of at least 11 types, are ubiquitous throughout the body, and perform a variety of functions. Phosphodiesterase type 5 (PDE5) is the predominant enzyme in the corpus cavernosum, and plays a crucial role in penile erection. Inhibitors of PDE5 are the most effective oral agents in the treatment of erectile dysfunction. Sildenafil, tadalafil, and vardenafil are all potent inhibitors of PDE5 and show the same mechanism of action, although they have some pharmacological differences that may translate into varying clinical effects.