The short interest data are out for the August 31 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 August 31 short interest data have been compared with the previous figures, and short interest in these selected stocks increased across the board for this settlement date.

Amgen Inc. (NASDAQ: AMGN) saw its short interest jump to 9.24 million shares from the previous level of 7.53 million. Shares closed Thursday at $153.14, in a 52-week trading range of $127.67 to $181.81.

Biogen Inc. (NASDAQ: BIIB) had its short interest rise to 3.86 million shares from the previous 2.68 million. Shares closed Thursday at $312.62, within a 52-week trading range of $265.00 to $480.18.

Celgene Corp. (NASDAQ: CELG) short interest for this settlement date increased to 12.50 million shares from the previous reading of 10.64 million. Since March, Celgene has recorded a few of its highest readings of the year. The mid-May level was the highest short interest reading year to date. Shares of Celgene closed Thursday at $122.97, in a 52-week range of $83.16 to $140.72.

Gilead Sciences Inc. (NASDAQ: GILD) saw its short interest rise to 25.65 million shares, from 21.73 million in the previous period. The late July reading was the lowest of the year. Shares closed Thursday at $107.25, in a 52-week trading range of $85.95 to $123.37.

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MannKind Corp. (NASDAQ: MNKD) saw its short interest increase to 126.70 million shares. The previous reading was 121.78 million. This is the second highest reading on the year. Shares closed Thursday at $3.75, in a 52-week trading range of $3.25 to $7.88.

Alexion Pharmaceuticals Inc. (NASDAQ: ALXN) short interest increased to 5.39 million, from the previous level of 4.61 million. The mid-June level was far and away the highest reading on the year, and since that time shares have backed off significantly. Shares closed Thursday at $171.65, in a 52-week range of $150.06 to $208.88.

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