It has been more than half a century since a drug has been approved specifically to treat lupus, but it looks like patients and investors won't have to wait much longer. A Food and Drug Administration advisory panel voted 13 to 2 to recommend that the agency approve Human Genome Sciences' (Nasdaq: HGSI) and GlaxoSmithKline's (NYSE: GSK) Benlysta.

The FDA's goal for making its decision -- a PDUFA date -- is Dec. 9. That's only three weeks away, so the agency may take a bit of extra time making its final decision. The FDA gave Benlysta a priority review -- six months instead of the traditional 10 months -- so a few extra days or weeks won't hurt anything.

The FDA doesn't have to follow its panel's recommendation -- just ask InterMune (Nasdaq: ITMN), Dendreon (Nasdaq: DNDN), and myriad others. But given the relatively positive briefing documents, the overwhelmingly positive advisory committee recommendation, and the unmet need, I have a hard time seeing the FDA turning the drug down based on effectiveness and safety.

Of course, there's always the risk that the FDA might have a problem with manufacturing or the REMS, but those are usually easy to fix. It doesn't look like Human Genome Sciences and Glaxo are going to have to run a new clinical trial to satisfy the FDA, which would be a longer delay for sure.

That doesn't mean that you should necessarily jump into Human Genome Sciences. With the company's market cap of $4.7 billion, there are plenty of sales already baked into the stock price; investors seem to agree that an FDA approval is all but certain. Glaxo might be interested in acquiring the drugmaker to get full rights to Benlysta, but buying based on expecting an acquisition is a dangerous game to play.

Assuming Human Genome Sciences doesn't get acquired and Benlysta is eventually a blockbuster, there's some growth left, but the meteoritic increase we've seen since before Benlysta phase 3 trials were a success -- the shares traded below $1 in March 2009 -- certainly won't continue. If you're going to invest, consider Human Genome Sciences for a long-term hold.

The Fool owns shares of and has written covered calls on GlaxoSmithKline, which is a Motley Fool Global Gains selection. Try any of our Foolish newsletter services free for 30 days. We Fools may not 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.

Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article.