Teva Pharmaceutical Industries Ltd, the worlds largest manufacturer of generic medications has been sued by Pfizer Inc, the manufacturer of the block buster impotence drug Viagra.

Teva is seeking approval from the US Food and Drug administration ( FDA ) to go to market with a copy of the drug ( Sildenafil Citrate ). Pfizers complaint is that the copy would infringe their patent that expires in 2019.

Generics maker Teva Pharmaceutical Industries based in Petah Tikva, Israel, have received preliminary approval to sell a version of sildenafil when another patent of Viagra expires in early 2012

Sales of Viagra which is a treatment for erectile dysfunction generated close to $2 billion  last year for Pfizer, including over $960 million in the U.S alone.

Teva has declined to comment on the latest complaint

Viagra, Cialis and Levitra are the three drugs currently used to treat erectile dysfunction ( ED )