What was Viagra's original purpose? Angina, the chest pain of heart disease. Sildenafil came out of a Pfizer programme in Sandwich, in the UK, that was looking for new angina medicines; it fell short there, and a side effect turned it into Viagra for erectile dysfunction, approved in 1998. In 2005 the same medicine, as Revatio, was approved for high blood pressure in the lungs.
What was sildenafil first developed for?
Angina. In the mid-1980s, "a very active cardiovascular research programme was based at the Pfizer European research laboratories in Sandwich, UK", and some of its scientists were looking for an alternative to nitrates, the standard angina medicines, whose effect fades when they are taken for long periods. "In 1986 Pfizer formed a project team of scientists at Sandwich, with the aim of developing a selective inhibitor of PDE5", the enzyme that switches off the signal nitrates use to relax blood vessels. The compound they chose was "initially named UK-92,480, but is now better known as sildenafil"; it was selected for development in 1989 and "eventually entered clinical trials in 1991" (Ghofrani et al., Nature Reviews Drug Discovery, 2006). The review, co-written by Ian Osterloh, who was responsible for Viagra's clinical development at Pfizer, sums the programme up as one "seeking drugs for angina pectoris".
Why didn't it become an angina medicine?
Because the results pointed elsewhere. Given into a vein to patients with angina, it had only "a moderate vasodilatory effect", and "by mid-1993, UK-92,480 was looking less promising as a new treatment for angina pectoris". The review gives two reasons: "The relatively short half-life indicated that treatment would have to be administered at least three times per day for the chronic treatment of angina", and "The demonstrated interaction with nitrates was also a factor complicating future drug development for cardiovascular indications" (Ghofrani et al.). That interaction still matters most today: people who use nitrates, often prescribed for angina, must not take medicines like Viagra (healthdirect).
How did it become a medicine for erectile dysfunction?
Through a side effect. In 1992, healthy volunteers taking repeated doses reported headaches, flushing, indigestion and muscle aches, and "Some volunteers also reported penile erections as a side effect". Pfizer ran its first study in men with erectile dysfunction in late 1993, and by 1997 "21 separate clinical trials had demonstrated the efficacy of sildenafil in various patient populations" (Ghofrani et al.). That work led to its FDA approval in 1998, on 27 March (Drugs@FDA — Viagra). How the side effect was noticed and tested is told step by step in how was Viagra discovered?
What is Revatio?
Sildenafil for high blood pressure in the lungs. Revatio "is a medicine used to treat adults and children from 1 year of age with pulmonary arterial hypertension (PAH, abnormally high blood pressure in the arteries of the lungs)", and the adult tablet is 20 mg (EMA — Revatio). The FDA approved Revatio 20 mg tablets on 3 June 2005 (Drugs@FDA — Revatio), and the European Commission authorised it throughout the European Union on 28 October 2005 (EMA — Revatio). Revatio is also on the Australian register (ARTG search). In the review's words, sildenafil "has evolved from a potential anti-angina drug to an on-demand oral treatment for erectile dysfunction (Viagra), and more recently to a new orally active treatment for pulmonary hypertension (Revatio)" (Ghofrani et al.).
What happened to the patent?
In the United States it ran until April 2020, not 2019 as this page used to say. Pfizer described its patent on the use of Viagra to treat erectile dysfunction as one "which expires in April 2020", a date that includes a period of paediatric exclusivity; a settlement let Teva launch a generic on 11 December 2017 (Pfizer, 17 December 2013). The older claim of a patent "in 1996" has no source we could verify, so we have removed it. The generic story is on is generic Viagra available in the USA?
The short answer
Viagra did not start out as a medicine for erections. Sildenafil was developed at Pfizer's Sandwich laboratories from 1986 as a possible angina medicine, fell short of that goal by 1993, and was approved for erectile dysfunction in 1998 after volunteers reported erections as a side effect; in 2005 it was approved again, as Revatio, for high blood pressure in the lungs. When it reached each market, Australia included, is on when was Viagra introduced to the market?, and the whole timeline is in our history of Viagra.
