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 POZEN (NASDAQ:ARLZ), a biopharmaceutical company developing therapies focused on treating acute and chronic pain, tumbled as much as 28% earlier in the trading session after receiving a complete response letter from the Food and Drug Administration in response to its new drug application for PA8140/PA32540.

So what: According to POZEN's press release, it received the CRL (a rejection letter from the FDA) for PA8140/PA32540, a secondary prevention treatment of cardiovascular disease for patients at high risk of developing aspirin-induced gastric ulcers, because of deficiencies at a third-party supplier of an active ingredient used in its drug. As the release notes, "Satisfactory resolution of deficiencies noted by the field investigator is required before the NDA may be approved." Most importantly, however, no clinical or safety deficiencies were noted with respect to either the 81 mg or 325 mg dosage.

Now what: While shareholders are plainly not happy with today's CRL, I would point out that the drug appears to be safe and effective at meeting its efficacy endpoint. What the real question is that shareholders should be asking is how serious these deficiencies are and how long they will take to fix. It appears shareholders may have a better answer to these questions when the company reports its quarterly results on May 8.

If you're a current shareholder I might be a bit disappointed today, but I would suggest not giving up so easily. POZEN has a globally successful U.S. partner in Sanofi (NASDAQ:SNY) for its experimental drug, and a therapy that tested strongly in late-stage studies. Furthermore, with peak sales potential of $400 million (a direct figure pulled from a POZEN presentation last April), there could be significant upside left in shares once this issue is resolved with the company valued at just $250 million as of this writing.