Pfizer (NYSE:PFE) has settled its long-standing feud with Teva Pharmaceutical (NYSE:TEVA) over the generic-drug maker's claims that Pfizer's U.S. patent on Viagra is invalid. Teva will be allowed to launch a generic version in the U.S. on Dec. 11, 2017, almost two and half years before Pfizer's exclusivity expires, the company announced today.

The erectile dysfunction drug has the same active ingredient as Pfizer's heart medication Revatio. The patent on the active ingredient, sildenafil citrate, already expired, but Pfizer received an additional patent on the use of the drug to treat erectile dysfunction, which gives it exclusivity until April 2020.

So-called "method of use" patents are typically hard to defend, but the validity of Pfizer's patent was upheld by a federal judge in 2011.

The settlement removes Pfizer's risk that Teva could win on an appeal and launch immediately. As part of the settlement, Teva will pay Pfizer an undisclosed royalty on the drug, so Pfizer may not give up all that much of its profit on Viagra even if a majority of the patients switch to the generic. When there's only one generic version on the market, the generic drug usually fetches over 90% of the branded drug price.

Viagra generated about $1.14 billion in U.S. sales last year and more than $2 billion worldwide.

-- Material from The Associated Press was used in this report.

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