A Supreme Court of Canada decision that invalidates a company's multimillion-dollar monopoly on the impotence drug Viagra has sent a tough warning to corporations about playing fast and loose with patent applications.

Ruling unanimously against Pfizer Canada Inc., the court said that judges will not tolerate patent-seekers attempting to conceal the key ingredients of their discoveries.

Patent legislation amounts to a quid pro quo that offers inventors an exclusive monopoly in return for the forthright disclosure of all the ingredients of their product in their patent applications, Mr. Justice Louis LeBel said, writing for the court.

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"If there is no quid – proper disclosure – then there can be no quo – exclusive property rights," he said.

Rival companies are allowed to see the patent applications and can use them to make their own versions.

Michael Geist, a University of Ottawa law professor specializing in technology, said the ruling "sends a strong message" to all companies or individuals who seek patents that they must provide full disclosure if they hope to benefit from patent protection.

The decision clears the way for inexpensive, generic versions of Viagra in Canada as soon as competitors can satisfy Health Canada requirements. The Canadian patent had not been due to expire until 2014.

David Aitken and Marcus Klee, lawyers with Osler Hoskin & Harcourt LLP who represented the appellant – Teva Canada Ltd. – said their client and other generic drug manufacturers are likely to move quickly to produce versions of Viagra.

Pfizer also faces probable lawsuits from any company that was prevented from making a Viagra-like drug since the company acquired its patent 18 years ago.

In arguing that the patent should be overturned, Teva said Pfizer took great pains in its application to obscure the importance of a crucial ingredient – sildenafil.

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"The argument was that sildenafil was hidden like a leaf in the forest," Mr. Aitken said. "Their patent application covered billions and billions of compounds, yet it only contained a very cryptic description of the compound that had actually been tested in impotent males and found to be effective."

A healthy patent system requires the frank sharing of information, Mr. Aitken said. "Many inventions are built on the shoulders of previous inventions. Failure to disclose stifles further research and development in the field."

Pfizer Canada made about $80-million last year on Viagra. The company announced last month that it is laying off 300 professionals, or 11 per cent of its Canadian work force, as it struggles to reduce costs to soothe the revenue erosion after the expiration of patents such as its blockbuster cholesterol-lowering drug, Lipitor.

In a statement Thursday, the company said it was disappointed with the ruling. "Pfizer will continue to vigorously defend against challenges to its intellectual property," it said.

Rhonda O'Gallagher, executive director of corporate communications at Pfizer Canada, could not exclude the possibility of further layoffs at the Canadian subsidiary. "We always take into account the possibility of losing exclusivity into our business planning processes," she said. "But we don't know if [this decision] will have a further impact. It is too soon to tell."

Pfizer scientsts had been investigating sildenafil as a cardiovascular drug when they stumbled across the use that made headlines around the world.

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"Our client is not the first company to have taken a run at this patent," Mr. Aitken said. "This is a landmark decision that will guide Canadian patent law for many years into the future."