The Miracle of Viagra

Erectile dysfunction is properly defined as the inability of a man to achieve or maintain an erection sufficient for his sexual needs or the needs of his partner. Studies show that about half of all men in the United States between the ages of forty and seventy have ED to some degree. ED is mostly the result of aging; however, physiological and psychological factors, such as high blood pressure and depression, can also lead to ED. In societies around the world, there is a constant consumer demand for various concoctions, herb or chemical, promising to restore a man’s libido to what it was when he was in his mid-twenties. Such a time machine has been made possible in this modern age, and it takes its form in a blue, di

In the male reproductive system, the biosynthetic NO is released locally from the corpus carvenosum upon stimulation, and cGMP acts as a vasodilator to produce a male erection. However, since all good things must come to an end, the cGMP molecule is quickly hydrolyzed by PDE5 to GMP, the inactive form. In normal males, this process is a vital regulatory mechanism that controls the level of cGMP in cells. However, men suffering from erectile dysfunction (ED) produce insufficient level of NO. The relatively few cGMP molecules produced are quickly hydrolyzed into GMP, and the erection is lost prematurely. Sildenafil binds to the active site of PDE5 and blocks its hydrolytic capability. Consequently, these relatively few cGMP molecules remain in their active form for a longer period of time, leaving the penis well erected for the couple to enjoy. However, in revisiting the theme of all good things must come to an end, the fate of sildenafil lies with the liver. Cytochrome p450 enzymes in the liver facilitate the breakdown of sildenafil into N-desmethylated sildenafil, an intermediate metabolite that will undergo further breakdown. Incredibly, N-desmethylated sildenafil retains forty percent of sildenafil’s affinity for PDE5! The discoverers of Viagra must be devoted followers of Don Juan, seeing how they have come across a love drug that is diehard as well!

The pyrazolopyrimidinone ring structure was further modified by substitution of a propyl group for a methyl group to further increase affinity and later addition of a sulphonamide group to reduce lipophilicity and increase solubility. In 1989, the team named the resulting compound sildenafil (Fig. 3). Through the entire course of its development, Sildenafil was filtered through approximately 1600 other compounds and was found to be the most promising candidate in fulfilling the initial goal of combating hypertension and angina. However, in true fashion of opportunists, unexpected results from years of phase trials persuaded the team to reinvent their expectation for sildenafil. Results showed the drug’s activity in treating patients suffering from angina was badly overestimated. Results also indicated a very interesting side effect of improving erectile function. Further tests on patients with ED revealed a direct correlation between drug dosage and erection period. March 27, 1998 marks the

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