The Supreme Court of Canada has invalidate Pfizer's Canadian patent on Viagra, citing the drug-maker's failure to disclose essential information about the main ingredient, sildenafil citrate, in the original application, which was filed in 1994 and granted in 1998. (CA 2163446) The appellant in the case was generic drug maker Teva Canada Ltd.
Pfizer holds several other patents related to Viagra, all of which are listed in the Canadian Drug Patent Register.
Here are a couple of stories from the Globe and Mail:
Supreme Court backs Canadian firm’s bid to make generic Viagra