Element of Pfizer's Viagra patent rejected

An appeals board within the US Patent and Trademark Office has partially rejected Pfizer's patent claim on its erectile dysfunction drug, Viagra (sildenafil), ruling that an element of the drug was not significantly different to the Chinese medicine, Yin Yang Huo (Horny Goat Weed), and did not represent a new invention.

In coming to its conclusion on the ruling, the appeals board stated that the patent claim was the next logical step up from using Yin Yang Huo in the treatment of erectile dysfunction. A chemical ingredient of the herb was found to be similar to an enzyme inhibitor found in Viagra.

The claim formed part of a 2002 lawsuit filed by Pfizer against Eli Lilly over its rival drug, Cialis. Pfizer has until April 12, to seek a rehearing or appeal against the decision.

The patent in question is due to expire in 2019. This ruling only concerns one element of Viagra, and Pfizer could therefore still use the patent to block generic competition from the duplication of the drug's active ingredient (sildenafil citrate).

Pfizer's revenue for 2009 included $1.89bn from the sale of Viagra.