Medical trivia: how Viagra was discovered

Viagra works by dilating blood vessels. It was originally developed as a treatment for hypertension (high blood pressure) and angina (chest pain associated with cardiovascular disease). Treating hypertension has been incredibly important at cutting the risk of heart disease, stroke, and kidney failure. Blood pressure control is extremely important for good health.

Anyway, in clinical trials, to Pfizer scientists’ disappointment, Viagra did not have much effect on blood pressure or angina. Part of doing a clinical trial entails collecting data on side effects. In those early angina trials, upon inquiring about unusual effects, scientists were surprised by a common reply: “You know, doc, it’s funny you should ask . . . .”

Cialis (generic name taladenafil, sold by Eli Lilly), also for erectile dysfunction, has the same mechanism of action as Viagra. Cialis was discovered by Glaxo Wellcome (a predecessor to GlaxoSmithKline). In 1996, Glaxo Wellcome saw the same side effect for Cialis that was seen with Viagra. Glaxo execs thought there would not be much commercial potential for such a product and dropped development. (Viagra had not yet been approved; that occurred on March 17, 1998). In 2011, Lilly’s worldwide sales of Cialis totaled $1.9 bn. As for Glaxo . . . Ooops.

Author’s note on the science: a structure in the penis, the corpus cavernosum, houses a network of blood vessels. Various stimuli produce chemical signals that lead to dilation of these blood vessels. The inflow of blood into the corpora cavernosa (plural) produces an erection. This is how Viagra, a blood vessel dilator (aka vasodilator), produces its effect.

Viagra was not the first vasodilator to be used to produce an erection. Alprostadil, a prostaglandin, is a potent vasodilator. Branded as Caverject, this was a very effective treatment for erectile dysfunction. The downside is that this drug must be injected directly into the penis. Needless to say, most men are not enthusiastic about this mode of delivery. Caverject users stood tall with pleasure (pun intended) when Viagra was approved.

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