The generic pharmaceutical giant has been trying to topple a method-of-use patent for the Pfizer (New York, NY, USA) erectile dysfunction (ED) drug that expires in October 2019, but the US District Court for the Eastern District of Virginia has decided that this should remain in force. The patent challenge was launched on the grounds that Pfizer had double-patented Viagra in the USA --one expiring in March 2012 to treat heart-related issues and the second in 2019--and that the second use patent was invalid; it also argued that Pfizer withheld information from the US Patent and Trademark Office. Those assertions were dismissed by the judge in the case.

Pfizer reported Viagra sales of US$495 million in the second quarter of 2011, a rise of 1%, and is Pfizer's sixth best-selling brand. Around the world, however, the product has already started to lose patent protection in some markets (notably Brazil in June 2010), with more to come by the end of 2012. The reaffirmation of its US patent position is therefore a big boost for the franchise, since more than 50% of Viagra's sales are made in the USA, accounting for $1 billion a year in turnover.

“We are pleased that the court recognized the validity and enforceability of our Viagra patent for the treatment of erectile dysfunction,” said Amy Schulman, executive vice president and general counsel for Pfizer in a press release issued yesterday. “Protecting the intellectual property rights of our innovative core is critical, and Friday's court decision acknowledges Teva's clear violation of our patent rights.”

The decision is also good news for Eli Lilly (Indianapolis, IN, USA), the manufacturer of Cialis (tadalafil), and Bayer (Leverkusen, Germany), who makes Levitra (vardenafil), two other ED drugs whose sales would sharply decline with the introduction of a generic replacement.

Sildenafil citrate, sold as Viagra, is a drug used to treat ED and pulmonary arterial hypertension (PAH). It acts by inhibiting cGMP-specific phosphodiesterase type 5, an enzyme that delays degradation of cGMP. This results in increased levels of cGMP, leading to smooth muscle relaxation (vasodilation) of the intimal cushions of the helicine arteries. This smooth muscle relaxation leads to vasodilation and increased inflow of blood into the spongy tissue of the penis, causing an erection.

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