The U.S. may be the largest drug market in the world, but the European Union isn't too shabby. Amgen (NASDAQ:AMGN) is headed there next with Nplate, its blood-clotting drug for idiopathic thrombocytopenic purpura (ITP) -- a disorder that involves the body destroying its own platelets.

On Friday, the Committee for Medicinal Products for Human Use (CHMP) recommended approval of the drug. Now Amgen just needs to wait until final approval by the European Medicines Agency (EMEA) before it can start negotiating with government-sponsored health plans.

Unlike in the U.S., where GlaxoSmithKline (NYSE:GSK) and Ligand Pharmaceuticals (NASDAQ:LGND) got their ITP drug Promacta approved last week, Amgen won't have to worry about competition from Promacta in the E.U. for awhile. Glaxo hasn't even submitted an application to E.U. officials yet, although it's planning on getting the packet in by the end of the year.

Amgen won't capture all of the ITP patients in Europe, estimated at 50,000. Its label is for second-line use. Patients who are stable on steroids or Genentech (NYSE:DNA) and Biogen Idec's (NASDAQ:BIIB) Rituxan aren't likely to switch. But there's still a subset of patients unable to boost their blood platelet levels who will certainly be willing to try Nplate.

Nplate isn't likely to become the next Enbrel for Amgen, given the small population it treats, but if Amgen can get it approved to treat other indications like myelodysplastic syndrome (MDS) -- another blood-cell-production problem -- it has a shot at hitting blockbuster status. Heading to Europe is a big step toward getting to that $1-billion-per-year threshold.

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Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. GlaxoSmithKline is a Motley Fool Income Investor recommendation. Biogen Idec is a Stock Advisor selection. The Fool has a disclosure policy.