Amgen's (Nasdaq: AMGN) investors have a little better idea of when the company's $3.6 billion Neupogen and Neulasta franchise might come under attack in the United States.

But only a little.

Amgen settled a patent dispute with generic-drug maker Teva Pharmaceuticals (Nasdaq: TEVA), allowing Teva to launch its copycat versions of either drug in November 2013. But because it's a settlement and not a decision by a court, there are no assurances that other generic-drug companies wouldn't try to invalidate the patents and launch before then. If they do, Teva is allowed to launch early as well.

On the other hand, it's possible that Teva might not even be able to launch in 2013 because it has yet to gain Food and Drug Administration approval for the drug. Generic-drug approvals are usually fairly routine, but Neupogen and Neulasta are protein-based drugs for which a pathway to generic approval is still being worked out.

Rather than wait for the FDA to determine exactly what the agency wants in a biosimilar application, Teva decided to just apply using the standard application for its version, called Neutroval. Whether it has enough data to justify a full approval remains to be seen. Teva was planning on using the same strategy to gain FDA approval of Neugranin, its version of Neulasta.

At this point, Teva could just wait for the FDA to set up a biosimilar pathway and then apply using that system. Neutroval is already approved in Europe, where a biosimilar pathway has been in place for years, under the brand name TevaGrastim. Assuming the FDA sets up similar requirements, Teva would seem to be home free.

Teva, Mylan (Nasdaq: MYL), Novartis (NYSE: NVS), and the rest of the companies working on biosimilars certainly hope that the FDA will have a biosimilar approval pathway in place and approvals rolling out the door by November 2013. But this is the FDA we're talking about; companies' hopes and dreams don't usually play into how fast the agency works.

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Fool contributor Brian Orelli holds no position in any company mentioned. Check out his holdings and a short bio. The Motley Fool owns shares of Teva Pharmaceutical Industries. Motley Fool newsletter services have recommended buying shares of Novartis and Teva Pharmaceutical Industries. Try any of our Foolish newsletter services free for 30 days. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.