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| Sildenafil (Viagra) |
Sildenafil, trade name VIAGRA, chemical name 5-[2-ethoxy-5-(4-methylpiperazin-1-ylsulfonyl)phenyl]-1- methyl-3-propyl-1,6-dihydro-7H-pyrazolo[4,3-d]pyrimidin-7-one, formula C22H30N6O4S, was discovered through a rational drug design programme by the pharmaceutical company Pfizer. It is a potent selective inhibitor of the enzyme phosphodiesterase (PDE-5), which destroys cyclic guanosine monophosphate (cGMP), itself a dilator of blood vessels in the body. Viagra thus allows cyclic GMP to persist and this property has led to its use for the oral treatment of male erectile dysfunction (N. K. Terrett, A. S. Bell, D. Brown, P. Ellis Bioorganic & Medicinal Chem. Lett., 1996, 6, pp.1819-1824). It is adminstered as the citrate.
