Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of Antares Pharma (NASDAQ:ATRS), a specialty biopharmaceutical company focused on developing self-administered and topical-gel medications, advanced as much as 14% after announcing the Food and Drug Administration's approval of its Otrexup injection for the treatment of adults with rheumatoid arthritis, adults with psoriasis, and children with polyarticular idiopathic arthritis. Shares have since given back most of their gains are now up just 4% as of this writing.

So what: Otrexup itself is a once-weekly subcutaneous injection self-administered by the patient. It will act as a second-line therapy for rheumatoid arthritis patients who are intolerant to oral methotrexate or who have demonstrated poor response. In addition, in human study trials Antares found that injectable methotrexate demonstrated increased bioavailability relative to oral methotrexate, giving the company hope that it will become a go-to medication for second-line rheumatoid arthritis disease control. Antares plans to launch Otrexup in early 2014.

Now what: There's absolutely no way to spin this other than the fact that it's great news for Antares and its shareholders. According to the company's own estimates, Otrexup could have peak sales potential ranging from $100 million to $200 million. At the midpoint of that guidance, and including its other approved products, Antares is currently valued at close to three times peak sales estimates. I'm not willing to go out on a limb and say Antares is richly valued yet -- but it's also not much of a bargain in my eyes, either. I believe we need to take a step back and see how well Antares executes the launch of Otrexup before we can have a really good bead on where it heads next.

Fool contributor Sean Williams has no material interest in any companies mentioned in this article. You can follow him on CAPS under the screen name TMFUltraLong, track every pick he makes under the screen name TrackUltraLong, and check him out on Twitter, where he goes by the handle @TMFUltraLong.

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