The company surged Monday on the news of Merck's (MRK) acquisition of Idenix Pharmaceuticals (IDIX). The stock continued to surge Tuesday after the FDA removed its clinical hold on sovaprevir, one of Achillion's four experimental hepatitis C treatments. The FDA had placed the hold in June because of abnormal liver results in patients. Achillion can now begin trials with a once-daily maximum dose of 200 mg of sovaprevir in hepatitis C patients and other healthy volunteers.
The stock was down 9.1% to $7.08 at 10:15 a.m.