Drug Insight: oral phosphodiesterase type 5 inhibitors for erectile dysfunction

Erectile dysfunction (ED) is a common medical condition that affects the sexual life of millions of men. At present, first-line oral pharmacotherapy for most patients with ED is a phosphodiesterase type 5 (PDE-5) inhibitor, of which three are currently available worldwide. Sildenafil (Viagra, Pfizer) has a very satisfactory efficacy-safety profile in all patient categories. The first PDE-5 inhibitor to reach the market, it is now the most widely prescribed oral agent for ED. Tadalafil (Cialis, Lilly ICOS) and vardenafil (Levitra, Bayer/GlaxoSmithKline) were introduced to the European Union and the US in 2003 and 2004, respectively. These three PDE-5 inhibitors share many characteristics, but each has unique features. This review describes the chemical, pharmacologic and clinical features of sildenafil, vardenafil and tadalafil as oral first-line treatments for ED. First, we describe the physiology of penile erection and PDE-5 inhibitor pharmacology, including chemistry, PDE selectivity, pharmacokinetics, and possible drug interactions. We then summarize data on the efficacy and safety profiles of the three PDE-5 inhibitors for the treatment of ED in the general population, in patients with diabetes mellitus and in men that have undergone bilateral nerve-sparing retropubic radical prostatectomy.