The short interest in biotech stocks is generally rising, judging by the short interest changes from August 15 settlement date versus the July 31 settlement date.

We have tracked the key short interest changes in the following biotech and emerging pharma companies: Alexion Pharmaceuticals Inc. (NASDAQ: ALXN), Amgen Inc. (NASDAQ: AMGN), Arena Pharmaceuticals Inc. (NASDAQ: ARNA), Biogen Idec Inc. (NASDAQ: BIIB), Celgene Corp. (NASDAQ: CELG), Dendreon Corp. (NASDAQ: DNDN), Gilead Sciences Inc. (NASDAQ: GILD), Illumina Inc. (NASDAQ: ILMN), Onyx Pharmaceuticals Inc. (NASDAQ: ONXX), Pharmacyclics Inc. (NASDAQ: PCYC), Regeneron Pharmaceuticals Inc. (NASDAQ: REGN), Vertex Pharmaceuticals Inc. (NASDAQ: VRTX) and VIVUS Inc. (NASDAQ: VVUS). We also tracked the iShares Nasdaq Biotechnology (NASDAQ: IBB) against the group.

Alexion Pharmaceuticals Inc. (NASDAQ: ALXN) short interest fell 10.0% between July 31 and August 15 to 5.28 million shares, the smallest number of shares sold short since the mid May reading.

Amgen Inc. (NASDAQ: AMGN) short interest fell 5.8% to 11.85 million shares. The average daily volume was the lowest it has been this year.

Arena Pharmaceuticals Inc. (NASDAQ: ARNA) short interest rose 9.5% to 42.75 million shares. Days to cover has increased to 3.

Biogen Idec Inc. (NASDAQ: BIIB) short interest fell 8.4% to 2.24 million shares. The average daily volume was the lowest it has been this year.

Celgene Corp. (NASDAQ: CELG) short interest rose 1.5% to 6.40 million shares.

Dendreon Corp. (NASDAQ: DNDN) short interest rose 6.1% to 43.37 million shares. Short interest has been rising since the end of May, and days to cover is more than 8. Short interest is 28.8% of the float.

Gilead Sciences Inc. (NASDAQ: GILD) short interest rose 16.6% to 21.05 million shares, the greatest number of shares sold short so far this year.

Illumina Inc. (NASDAQ: ILMN) short interest rose 3.1% to 22.10 million shares. Days to cover is 25 and short interest is 18.3% of the float.

Onyx Pharmaceuticals Inc. (NASDAQ: ONXX) short interest fell 3.2% to 5.74 million shares. Short interest was 9.1% of the float.

Pharmacyclics Inc. (NASDAQ: PCYC) short interest rose 9.1% to 5.33 million shares. Days to cover rose from 5 at the July 31 reading to 7 by August 15. Short interest was 9.8% of the float.

Regeneron Pharmaceuticals Inc. (NASDAQ: REGN) short interest rose 0.1% to 4.97 million shares. Days to cover rose from 4 at the July 31 reading to 7.

Vertex Pharmaceuticals Inc. (NASDAQ: VRTX) short interest rose 21.8% to 6.39 million shares. After falling in the previous four periods, short interest has risen again.

VIVUS Inc. (NASDAQ: VVUS) short interest rose 18.5% to 16.44 million shares, the highest number of shares sold short since mid March. Short interest was 16.5% of the float.

To show how the sector has held up: the iShares Nasdaq Biotechnology (NASDAQ: IBB) ETF closed at $134.83 on the same date. Its current 52-week range is $87.67 to $138.75.

Trey Thoelcke

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