Sildenafil citrate: How Pfizer sold the wrong drug to the right people!

In 1989, researchers Peter Dunn and Albert Wood, working at the Pfizer’s research facility at Kent, England, were able to synthesize a drug that could be used to treat patients with high blood pressure  and chest pain. Called Sildenafil citrate, this drug could inhibit functioning of the enzyme, cGMP-specific phosphodiestrase type 5, simply called PDE-5, making blood vessels more receptive to nitric oxide in the blood, further leading to the relaxation of the arterial wall and regulation of blood pressure. Like every other drug discovery, Sildenafil citrate, too, now had to go through rigorous clinical trials before being able to actually help patients.

Structure of Sildenafil citrate

Phase I clinical trials were conducted at a hospital in Wales which did not progress very well. In addition to the regular side-effects such as headache, impaired vision and indigestion, sildenafil was also found to result in unintended penile erections in male subjects. What was even worse for Pfizer is that the study found that the drug did not make a significant contribution to treating angina in patients. Phase II trials were also conducted for the drug, but data from the study could not show a correlation between administration of sildenafil and improvement in cases of angina. However, instead of stopping the project altogether, the company invested time and effort in recognizing the cause for these side effects.

Investigations by Pfizer lead them to the fact that PDE-5 is largely located in the arterial wall of the lungs and smooth muscles of the male penis. In addition to acting on the arterial walls, Sildenafil also found its way to these smooth muscles and acted exactly the way it was expected to behave.  Pfizer realised that the erection seen in patients was no side-effect at all and they had stumbled upon a major discovery in the field of reproductive medicine. After a few more years of research, a patent application in the year 1996 and approval of US FDA in 1998, Pfizer presented the world with a diamond shaped, blue pill, commonly known as Viagra.

The Blue Pill

Although Viagra was introduced as a prescription drug, Pfizer made every effort to market it to every household they could, not only in the United States but also worldwide. The marketing of the drug was done so well that within a couple of years of its release, Viagra accounted for 92% of the global prescriptions for erectile dysfunction and even though its market share has dropped is helping Pfizer make millions every year.  Since PDE-5 is also seen on the arterial walls of the lungs, Pfizer also sells another preparation of Sildenafil, called Revatio, for treatment of rare condition called pulmonary arterial hypertension or PAH. Both medications, Viagra and Revatio, are evidence that Pfizer put the information they got out of their initial failures to good use and leave a lot to be learnt from this story.

While the drug shows remarkable improvement in people affected by erectile dysfunction, there is hardly any evidence to show that it works for healthy individuals.  Originally Viagra was available only by prescription, but since several other brands are now available in the market, sildenafil citrate can be bought anonymously over the internet or also as an over-the-counter drug, leading to the use of this drug by normal healthy individual  as an aphrodisiac. This un-prescribed and unsupervised usage of the drug, borders on the lines of addiction and drug abuse.  Apart from recreational purposes, this drug can also be used in recovery from jet lags, increasing athletic performance and also extending shelf life of cut flowers, strawberries, broccoli and other perishables. Ideas for home science, anyone?

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