Why Achillion Pharmaceuticals Plunged for a 4th Consecutive Day

What happened

Shares of Achillion Pharmaceuticals (NASDAQ: ACHN) plunged 14.9% as of 3:29 p.m. EST on Thursday. Today's sharp decline marked the fourth consecutive day for the biotech's share price to fall by a double-digit percentage.

There weren't any new developments for Achillion. The sell-off started on Monday when investors were anxious about the company's pipeline update scheduled for after the market close. Achillion's announcement that it wouldn't move forward with a late-stage study of lead candidate ACH-4771 as a monotherapy in treating rare blood disorder paroxysmal nocturnal hemoglobinuria (PNH) kept the downward momentum going on Tuesday and Wednesday.

In addition, the broader market decline today didn't help Achillion. Market corrections can sometimes take their biggest toll on stocks that were already weakened.

So what

Achillion's decision to abandon any plans to advance ACH-4771 as a monotherapy in treating PNH was bad news, for sure. It's not surprising that the stock plummeted on the news. The main question now is can Achillion bounce back?

The good news for Achillion is that it still has opportunities to make a comeback. It's not over for ACH-4771. Achillion still thinks the drug could be effective as part of a combination therapy. The biotech is continuing to evaluate ACH-4771 in combination with Alexion's Soliris in treating PNH in a phase 2 study.

Also, Achillion's phase 2 studies of ACH-4771 in treating C3 glomerulopathy (C3G) still is in progress. The company plans to finalize details for a late-stage clinical trial for the drug in the C3G indication next year.

In addition, Achillion's pipeline includes a couple of other next-generation Factor D inhibitors -- ACH-5228 and ACH-5548. The biotech expects to initiate a phase 1 study of ACH-5528 in the first quarter of 2019 and a phase 1 study of ACH-5548 in Q1 of 2020.

Now what

Next year will be important in determining what the prospects for the biotech might be for Achillion. The company reports top-line data from its phase 2 combo study of ACH-4771 and Soliris in PNH and wraps up its phase 2 study of ACH-4771 in treating C3G.

For now, though, there are too many unknowns for new investors to buy Achillion. Even though the biotech has lost more than half its market cap this week, it's hard to call Achillion a bargain with the considerable uncertainty for its pipeline candidates.

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Keith Speights has no position in any of the stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. The Motley Fool has a disclosure policy.