Biotech Stock Mailbag: Furiex, La Jolla Pharma, Sarepta

(TheStreet) -- This week's Biotech Stock Mailbag opens with an email from Bob P.:

Adam, I missed the big move in Furiex Pharmaceuticals (FURX) because I didn't know about their diarrhea drug. What is the potential for this stock to move higher? Am I too late or is there more upside to be gained in owning Fuirex at these stock levels? Thank you for your consideration of my questions.

You missed making the easy money in Furiex. Sorry. If it's any consolation, lots of other investors missed Furiex, too. Like you, I had never heard of Furiex until Tuesday when its executives called me to discuss the results -- under embargo -- from the phase III studies of eluxadoline in diarrhea-predominant irritable bowel syndrome. I wrote about the eluxadoline study Wednesday -- the eluxadoline data looked really good -- but still, I did not expect to see Furiex shares more than double in a single day.

At Thursday's intraday price of $107 per share, Furiex's market cap stands at $1.1 billion. Bulls will say the stock has more upside because the commercial market opportunity for a drug to treat diarrhea-predominant irritable bowel syndrome (IBS-d) is large. There are 15 million people with IBS-d in the U.S., another 13 million in Europe, Furiex estimates. If 2% of those IBS-d patients are treated with eluxadoline at a cost of $3,000 per year (equal to the annual cost of Ironwood Pharmaceuticals' (IRWD) Linzess for constipation-predominant IBS), then you're looking at $1.7 billion in sales.

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