Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of Achillion Pharmaceuticals (NASDAQ:ACHN), a biotechnology company focused on the development of hepatitis-C and bacterial infection treatments, plummeted as much as 26% after the company updated the status of its lead compound, sovaprevir, previously known as ACH-1625.

So what: According to the press release from Achillion before the opening bell, sovaprevir has been placed on clinical hold by the Food and Drug Administration due to elevated liver enzymes being discovered in a phase 1 drug-to-drug interaction study with atazanavir. Specifically, while the interaction study was ongoing, ALT liver enzyme levels rose in some subjects, although the company notes no serious adverse events were reached. Achillion's press release also points out that the FDA is allowing the company to continue enrollment and mid-stage trials of ACH-3102 in combination with sovaprevir for the treatment of genotype 1 hepatitis-C.

Now what: The FDA has certainly been clinical-hold-happy in the hepatitis-C sector over the past year, placing holds on three separate Idenix Pharmaceuticals (NASDAQ: IDIX) compounds and witnessing the shelving of Bristol-Myers Squibb's (NYSE:BMY) BMS-986094 due to the death of a patient in trials. But we also know that the FDA will not take safety lightly with regard to treating hepatitis C, and this setback only further puts Achillion behind its peers. It's looking very likely that Gilead Sciences and AbbVie are going to get a running start with their potential HCV blockbusters, which may leave Achillion in the dust.

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