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 rose 2.0% between August 31 and September 14 to 5.38 million shares. Days to cover has risen to almost six.
Amgen Inc. (NASDAQ: AMGN) saw short interest decline 2.2% to 12.61 million shares. Days to cover slipped to less than three.
Arena Pharmaceuticals Inc. (NASDAQ: ARNA) short interest rose 4.0% to 45.67 million shares. The average daily volume was the lowest it has been since April. But short interest was 21.2% of the float.
Biogen Idec Inc. (NASDAQ: BIIB) shares sold short grew 4.8% to 2.22 million. Short interest was 1.0% of the float.
Short interest in Celgene Corp. (NASDAQ: CELG) rose 3.1% to 6.05 million shares.
Dendreon Corp. (NASDAQ: DNDN) short interest increased 1.8% to 43.08 million shares. This was 28.6% of the float.
Gilead Sciences Inc. (NASDAQ: GILD) short interest was up 9.3% to 20.61 million shares. Days to cover slipped to about three.
Illumina Inc. (NASDAQ: ILMN) saw short interest rise 8.8% to 25.77 million shares. That was the fifth consecutive period of increasing short interest. Short interest was 21.3% of the float.
Onyx Pharmaceuticals Inc. (NASDAQ: ONXX) shares sold short increased 2.6% to 5.49 million. Days to cover jumped above five. Short interest was 8.6% of the float.
Pharmacyclics Inc. (NASDAQ: PCYC) short interest retreated 5.7% to 4.91 million shares. Days to cover fell to less than five. Short interest was 9.0% of the float.
Regeneron Pharmaceuticals Inc. (NASDAQ: REGN) short interest rose 8.4% to 5.19 million shares. Short interest was 6.9% of the float.
Short interest in Vertex Pharmaceuticals Inc. (NASDAQ: VRTX) grew 2.8% to 6.47 million shares. Days to cover is about five.
VIVUS Inc. (NASDAQ: VVUS) short interest was up 2.1% to 16.07 million shares. Days to cover jumped to about 10. Short interest was 16.1% of the float.
To show how the sector has held up: the iShares Nasdaq Biotechnology (NASDAQ: IBB) ETF closed at $141.76 on the same date. Its current 52-week range is $87.67 to $145.23.
Trey Thoelcke