The Discovery of Viagra
It Wasn’t Originally Intended to Treat Sexual Dysfunction.
The development of medicinally effective drugs is a vast worldwide industry, employing millions of scientists and spending vast fortunes in its pursuit of chemicals which will treat or cure medical complaints. This effort is driven as much by economics as by the desire to ease the lot of sufferers. The discovery of a new drug capable of treating a common ailment is worth vast quantities of money.
Lead Compounds
The science of pharmaceuticals has developed greatly in recent decades. The study of the pathways of diseases and the sophisticated molecular design techniques mean that chemicals can be found which may help in the treatment of a disease. These chemicals are called “lead compounds”; molecules which have some activity in the treatment of a medical condition, but need further work to make them more effective or to reduce the side effects.
Trials
Scientists take these lead compounds and synthesise many similar compounds, in the search for a usable drug. Many hundreds or thousands of compounds can be tried before an effective treatment is discovered. Often all are found to be useless and the research written off. This nearly happened to the compound now known as Viagra.
Hypertension
In the late 1980s, a Pfizer research group were looking for a compound which would treat hypertension. They were working on a method to enhance the activity of a compound called “atrial natriuretic peptide” (ANP). This compound was a natural diuretic, causing the kidneys to produce more urine, but it also relaxed blood vessel walls. So a drug which enhanced this activity would reduce high blood pressure.
Angina
Study of the mechanism by which ANP worked eventually led the team to consider lead compounds which would reduce the activity of one of a group of enzyme called “phosphodiesterases”(PDEs), which was involved in the mechanism. Lead compounds were found which inhibited the activity of PDE-5, which was involved both in the muscles in blood vessels and in platelets. These compounds had the potential to treat both thrombosis (blood clots caused by platelets) and angina (by increasing blood flow to the heart).
Ineffective
Attention had changed from the treatment of hypertension to the treatment of angina for various reasons, another common occurrence in the development of drugs. A hopeful lead compound, glamorously named UK-92,480, was taken to the next stage of clinical trials in 1989. It did not, however, live up to expectations, proving to be ineffective in the treatment of angina.
Erections
The compound was almost binned, but one side comment in some of the trials was that after four or five days of taking the drug, penile erections were observed. This attracted the attention of some of the Pfizer scientists who realised that the inhibition of the activity of PDE-5 was overcoming a proposed cause of erectile dysfunction.
Biological Cause
At the same time scientists were proposing that erectile dysfunction could have a biological cause and not just the psychological cause proposed up until that time. This led to the Pfizer scientists taking the decision to undertake trials with men suffering erectile dysfunction.
Release
The trials were successful and after further tests and development Viagra was released as a prescription drug, changing the lives of many men who had been struggling with impotence for years.
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