As of 2003, two new medications for erectile dysfunction have finished with their testing stages and have been approved by the FDA – vardenafil (Levitra, created by Bayer) and tadalafil (Cialis, created by Lilly/ICOS). Just like sildenafil (Viagra, manufactured by Pfizer), which was approved 5 years earlier, these two new drugs are PDE-5 inhibitors. There are several similarities among these three drugs and they all basically work the same way – increasing penile blood flow to produce firmer and longer-lasting erections. But there are also several important differences between them that potential users should consider.
Brindley’s Contribution to Erectile Dysfunction Treatment
In 1983, a British physiologist named Giles Brindley dropped his pants in front of a stunned audience and showed them his erect penis, the result of phentolamine. This demonstration inspired the advancement of modern treatments for ED. Brindley had injected a vasodilator into his penis, which used corporal smooth muscle relaxation. Brindley’s discovery led to the development of the modern ED drugs used today, which are PDE-5 inhibitors.
How PDE Inhibitors Work
PDE or phosphodiesterase is an enzyme produced by the penis that is responsible for breaking down cyclic guanosine monophosphate or cGMP, which is a chemical that increases blood flow to the penis. It is the direct intracellular mediator in the nitric oxide pathway, which scientists discovered in 1998 – leading them to a Nobel Prize.
The nitric oxide pathway is in several organ systems, and there are several kinds of PDEs that have been identified. PDE type 5 is generally found in the penis, specifically in the smooth muscle of the corpus cavernosum. Its role is to break down cGMP and end an erection after ejaculation. Sometimes there is too much PDE-5 which prevents an erection from developing at all. The three ED medications – Viagra, Levitra and Cialis – are all PDE-5 inhibitors, thus allowing increased blood flow to the penis when sexually aroused.
Summary:
All three drugs are relatively safe, provided they are not taken with nitrates. The combination of any of these medications with a nitrate will almost surely result in severe hypotension. Besides the longer history of Viagra and the longer duration of Cialis, all three ED medications have more or less the same results. With more choices now, there will be more competition among these drugs, and the manufacturers will be encouraged to improve their products more.