A Canadian federal court on Thursday upheld pharmaceutical giant Pfizer's patent for Viagra, dashing generic drug maker Novopharm's longing for sales of cheaper erection drugs.
Judge Michael Kelen said in his decision that Novopharm failed to demonstrate the Pfizer patent was invalid.
He ordered Canada's health minister not to grant the generic drug maker's request for special permission to manufacture a Viagra knock-off until the Pfizer patent expires in 2014.
Pfizer had filed the application to prohibit Novopharm from introducing a generic version of the hugely popular drug.
Sildenafil, the key ingredient in Viagra, was initially developed by Pfizer in the mid-1980s as one of a number of compounds for the treatment of hypertension and angina.
Angina patients unexpectedly experienced erections while being treated with sildenafil to lower their blood pressure, and so it was marketed to treat erectile dysfunction.
In its submissions, Novopharm, a subsidiary of the world's largest generic drug-maker Teva Pharmaceutical, questioned the timing of patent filings around Pfizer's discovery of the active ingredient in Viagra.
But in his decision, Judge Kelen said: "The court concludes that the applicants have met their legal burden to establish the validity of the patent."