Rising short-interest indicates bearishness for the company is building up by investors. Between November 30 2012 and December 14, short-selling increased between 1% and 15% for a number of biotech companies. Rising short-selling could mean upside if the prospects for the companies improve.

The short-selling volume, sorted by change, is listed below:

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Are short-sellers wrong? Below is a summary explaining why investors are negative on some of these companies.

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Amarin Corporation (AMRN) investors were disappointed that the company will be hiring its own sales force. Amarin has yet to announce a partner, which added to the disappointment. The company recently submitted a supplemental New Drug Application to the FDA for Chemport, Inc. The company is a supplier for an additional active ingredient for Vascepa.

Bearishness rose by 8% for Savient Pharmaceuticals, Inc. (SVNT). In November, the company reported quarterly earnings that missed estimates by $0.08 per share, while revenue of $4.5M missed estimates by $1.3 million.

Amgen Inc. (AMGN), whose market share is $65 billion, continued to declined recently. The company pleaded guilty and settled a criminal and civil liability for promotional activities around Aranesp. The settlement amount is $762 million.

Short-selling increased 5% for Dendreon Corp. (DNDN). Shares rallied 41% from a low. The company sold its immunotherapy manufacturing facility for $43M.

Exelixis, Inc. (EXEL) shares continued lower after bears covered the bets. After rising to $5, shares traded recently at $4.51. On November 30, the company said it received approval for a drug to treat a rare type of thyroid cancer.

Avanir Pharmaceuticals (AVNR) reportedquarterly earnings in mid-December that missed estimates, although revenue was higher than expected. The company reported revenue of $13.5 million.

Arena Pharmaceuticals, Inc. (ARNA) is the maker of Belviq, a drug used to treat obesity. Its partner, Eisai, wants to get faster approval, which would mean the drug would be available at pharmacies on February 7 2013.

(List Average 1-Year Return:  62%)

Additional Observations

Arena shows great promise in further upside. Its competitor , VIVUS (VVUS) saw short-selling decline, but investors should add Arena to their watch list. In its last quarter, Arena reported revenue that missed estimates, but earnings per share surprised investors. Responders who took the drug reported an average weight-loss of 11%.

In 2013, sales of Belviq should begin to support a higher share price. Arena is just waiting on the DEA scheduling right now. Also in the pipeline and in phase 1 trial is PAH APD8111, which is being tested for the treatment of autoimmune disease. If successful, this would broaden Arena’s product line.

Written by Kapitall’s Chris Lau