The short interest data are out for the May 15 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 May 15 short interest data have been compared with the previous figures, and for most of the selected stocks, short interest is down.

Amgen Inc. (NASDAQ: AMGN) saw its short interest drop to 8.85 million shares from the previous reading of 9.21 million. Shares closed Wednesday at $160.44, in a 52-week trading range of $114.93 to $173.60.

Biogen Inc. (NASDAQ: BIIB) saw its short interest increase to 3.04 million shares from the previous 2.98 million. The company was slowly approaching the lower part of its short interest range from back in November, and now it is seemingly returning to more normalized levels. Shares closed Wednesday at $402.92, within a 52-week trading range of $290.85 to $480.18.

Celgene Corp. (NASDAQ: CELG) short interest increased for this settlement date, to 16.27 million shares. The level for the previous settlement date was 14.00 million. Since March, Celgene has recorded a few of its highest readings of the year, barring a spike last June. However, the current level is the highest short interest reading on the year. Shares of Celgene closed Wednesday at $116.02, in a 52-week range of $75.62 to $129.06.

Gilead Sciences Inc. (NASDAQ: GILD) saw its short interest jump to 60.05 million shares from 55.51 million in the previous period. Shares closed Wednesday at $112.46, in a 52-week trading range of $78.50 to $116.83.

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MannKind Corp. (NASDAQ: MNKD) saw its short interest increase to an even higher level on the year, some 112.95 million shares. The previous reading was 100.93 million shares. Short interest for MannKind appears to have steadily increased to its 52-week high as investors remain pessimistic. Shares closed Wednesday at $5.27, in a 52-week trading range of $3.46 to $11.48.

Alexion Pharmaceuticals Inc. (NASDAQ: ALXN) short interest increased a whopping 5 million shares or so to 7.23 million, up from the previous level of 2.98 million. This current level is far and away the highest reading on the year. Shares closed Wednesday at $168.12, in a 52-week range of $150.06 to $203.30.

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