Pfizer’s patent on sildenafil citrate expired in some member countries of the EU, Austria, Denmark, France, Germany, Ireland, Italy, The Netherlands, Spain, Sweden, the United Kingdom and Switzerland on 21 June 2013. A UK patent held by Pfizer on the use of PDE5 inhibitors (see below) as treatment of impotence was invalidated in 2000 because of obviousness; this decision was upheld on appeal in 2002.
In 1992, Pfizer filed a patent covering the substance sildenafil and its use to treat cardiovascular diseases. This patent was published in 1993 and expired in 2012. In 1994, Pfizer filed a patent covering the use of sildenafil to treat erectile dysfunction. This patent was published in 2002 and will expire in 2019. Teva sued to have the latter patent invalidated, but Pfizer prevailed in an August 2011 federal district court case.
The patent on Revatio (indicated for pulmonary arterial hypertension rather than erectile dysfunction) expired in late 2012. Generic versions of this low-dose form of sildenafil have been available in the U.S. from a number of manufacturers, including Greenstone, Mylan, and Watson, since early 2013. No legal barrier exists to doctors prescribing this form of sildenafil “off label” for erectile dysfunction, although the dosage typically required for treating ED requires patients to take multiple pills.
In Canada, Pfizer’s patent 2,324,324 for Revatio (sildenafil used to treat pulmonary hypertension) was found invalid by the Federal Court in June 2010, on an application by Ratiopharm Inc.
On November 8, 2012, the Supreme Court of Canada ruled that Pfizer’s patent 2,163,446 on Viagra was invalid from the beginning because the company did not provide full disclosure in its application. The decision, Teva Canada Ltd. v. Pfizer Canada Inc., pointed to section 27(3)(b) of The Patent Act which requires that disclosure must include sufficient information “to enable any person skilled in the art or science to which it pertains” to produce it. It added further: “As a matter of policy and sound statutory interpretation, patentees cannot be allowed to ‘game’ the system in this way. This, in my view, is the key issue in this appeal.”
Teva Canada launched Novo-Sildenafil, a generic version of Viagra, on the day the Supreme Court of Canada released its decision. To remain competitive, Pfizer then reduced the price of Viagra in Canada. However, on November 9, 2012, Pfizer filed a motion for a re-hearing of the appeal in the Supreme Court of Canada, on the grounds that the court accidentally exceeded its jurisdiction by voiding the patent. Finally, on April 22, 2013, the Supreme Court of Canada invalidated Pfizer’s patent altogether.