Christmas came really early for GlaxoSmithKline (NYSE:GSK) and Ligand Pharmaceuticals (NASDAQ:LGND), and the drugmakers got exactly what they wanted: favorable news from the jolly old elves at the Food and Drug Administration.

After months of delays, the agency finally approved Promacta, their treatment for blood-clotting disorder idiopathic thrombocytopenic purpura (ITP). Moving swiftly, Glaxo expects to have the drug on the market next week. It's certainly had plenty of time to get ready, since the original PDUFA date was back in June.

Promacta will be going head-to-head with recently approved Nplate from Amgen (NASDAQ:AMGN). Getting a later start will make it harder on Glaxo and Ligand, but Promacta is taken orally, which should be more appealing to patients than injection-only Nplate.

The approval is great news, especially for Ligand, which will pick up a $2 million milestone payment and tiered royalties of 5%-10% on net sales. But the real benefit to both companies could come from expanding Promacta into other indications, since there are only 60,000 individuals diagnosed with chronic ITP in the U.S. Among other possible applications, Glaxo is currently testing Promacta in hepatitis C patients, to see whether it can help boost their blood platelet levels while they use antiviral therapies like Roche's Pegasys and Schering-Plough's (NYSE:SGP) Pegintron.

Even with its large share-price jump today (up 44% in late trading), Ligand's shares are still below their June prices, before the delay in approval. That just goes to show how crazy this market really is. Will Promacta really have lower sales just because the U.S. is entering a recession? Perhaps slightly so, but not nearly to the degree that investors have seemingly priced in.

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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 pick. The Fool has a disclosure policy.