Achillion Pharmaceuticals Inc. said Friday that the Food and Drug Administration is keeping a clinical hold in place on a study of its potential hepatitis C drug sovaprevir.
When the FDA issues a clinical hold, a drug developer must delay or suspend their investigation. Achillion said it will keep working to resolve the hold.
The company's shares fell 46 percent to $3.90 in after-hours trading. Shares closed Friday at $7.24, down 9.6 percent this year.
The FDA put a hold on an early-stage study of sovaprevir in July after researchers saw high levels of liver enzymes in multiple patients using the drug known as sovaprevir, along with a second drug. It allowed another study involving sovaprevir to continue.
The FDA kept the hold on after reviewing the company's response to issues it had noted.
The company, based in New Haven, Conn., also develops drugs for treatment of resistant bacterial infections. It said that it is in a position to start studies of other drugs it has developed to treat hepatitis C.