The short interest data are out for the February 27 settlement date. Biotech companies are considered a riskier group of stocks, with big upside and big downside. FDA rulings can make or break them. A single failed clinical trial can mean disaster for a stock. 24/7 Wall St. has reviewed the top biotech companies, without focusing on speculative companies.

The February 27 short interest data have been compared with the mid-February figures, and across the board, all the selected stocks have seen their short interest increase.

Amgen Inc. (NASDAQ: AMGN) saw its short interest increase to 10.3 million shares, with 3.1 days to cover. The previous short interest reading was 9.8 million with 2.5 days to cover. The short interest for Amgen took a dip to its lowest levels in the four settlement dates between December and January, recording the lowest levels on the year, with the lowest level being at the tail-end of January. Shares closed Tuesday at $153.58, in a 52-week trading range of $108.20 to $173.14.

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Biogen Idec Inc. (NASDAQ: BIIB) saw its short interest increase slightly to 3.4 million, with 3.3 days to cover, from the previous level of 3.3 million shares with 1.9 days to cover. Shares closed Tuesday at $414.20, within a 52-week trading range of $272.02 to $425.70.

Celgene Corp. (NASDAQ: CELG) saw a short interest increase for this settlement date, up to 12.8 million shares with 2.7 days to cover. The level for the previous settlement date was 11.1 million with 1.9 days to cover. Shares of Celgene closed Tuesday at $118.33, in a 52-week trading range of $66.85 to $125.45.

Gilead Sciences Inc. (NASDAQ: GILD) saw its short interest increase to 56.2 million with 6.7 days to cover, from 55.1 million with 3.2 days to cover. Investors seem to have backed off shorting this stock in September, when shares were poised to hit 52-week highs, but it is looking like the short interest is starting to pile back on at these raised levels. Shares closed Tuesday at $98.83, in a 52-week trading range of $63.50 to $116.83.

Mannkind Corp. (NASDAQ: MNKD) saw its short interest rise to 90.7 million shares, with 17.0 days to cover. The previous reading was 86.1 million, with 9.3 days to cover. The current short interest reading for Mannkind is the 52-week high by roughly 4 million. Shares closed Tuesday at $5.47. The 52-week trading range is $3.80 to $11.48.

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Alexion Pharmaceuticals Inc. (NASDAQ: ALXN) short interest increased to 3.2 million shares with 3.7 days to cover, up from the previous level of 3.1 million with 2.2 days to cover. There has been a trend since mid-November wherein the short interest has had some of the lowest readings for the past 52-weeks. Shares closed Tuesday at $181.28, in a 52-week trading range of $136.37 to $203.30.

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