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Viagra" redirects here. For the Russian/Ukrainian girl group also known as "VIA Gra", see Nu Virgos. Sildenafil Systematic (IUPAC) name 1-[4-ethoxy-3-(6,7-dihydro-1-methyl-7-oxo-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-5-yl)phenylsulfonyl]-4-methylpiperazine citrate Identifiers CAS number 139755-83-2 ATC code G04BE03 PubChem 5281023 DrugBank APRD00556 ChemSpider 56586 Chemical data Formula C22H30N6O4S  Mol. mass base: 474.6 g/mol SMILES eMolecules & PubChem Pharmacokinetic data Bioavailability 40% Metabolism Hepatic (mostly CYP3A4, also CYP2C9) Half life 3 to 4 hours Excretion Fecal (80%) and renal (around 13%) Therapeutic considerations Licence data EU EMEA:link, US FDA:link Pregnancy cat. B(US) Legal status ℞ Prescription only Routes Oral Sildenafil citrate, sold as Viagra, Revatio and under various other trade names, is a drug used to treat erectile dysfunction and pulmonary arterial hypertension (PAH). It was developed and is being marketed by the pharmaceutical company Pfizer. It acts by inhibiting cGMP specific phosphodiesterase type 5, an enzyme that regulates blood flow in the penis. Since becoming available in 1998, sildenafil has been the prime treatment for erectile dysfunction; its primary competitors on the market are tadalafil (Cialis) and vardenafil (Levitra).