Pfizer Inc., the pharmaceutical company that manufactures the erectile dysfunction medication Viagra has gone to court against Teva Pharmaceuticals International Ltd, the largest generic drug manufacturer in the world.  The legal battle is all about exclusivity rights for the production of Viagra which Pfizer is fighting to keep a hold of until 2019. Currently, Pfizer sells about $1 billion worth of Viagra a year in the USA alone, amounting to 2.5% of its annual sales.  Therefore, it is understandable why they are trying so hard to maintain their patent. The original patent Pfizer won in the 1990s for the compound Sildenafil is not in dispute. This was for the treatment of high blood pressure and other heart problems. However, during its clinical trials it soon became apparent that there was an unexpected side effect of the medication, instant erections. Pfizer fought for years in court to protect the lucrative market born of this serendipitous research and eventually won a second patent in 2002 that is due to expire in 2019. Teva contend that this second patent is invalid, and that that anyone schooled in drug research would have figured out that the compound would help with erectile dysfunction. They hope that Pfizer’s exclusivity rights will expire in March 2012. However,  Pfizer have sued Teva claiming their patent was valid and would be infringed if Teva produced a generic version of the Viagra.