AbbVie Inc. (NYSE:ABBV) shed $5.56 (10%) to $48.27 and Enanta Pharmaceuticals Inc. (NASDAQ:ENTA) plummeted $16.35 (41%) to $23.90 on Thursday after FDA issued a safety warning linking HCV therapies Viekira Pak and Technivie to cases of serious liver injury in cirrhotic HCV patients and required AbbVie to add information regarding liver injury risks to both drugs' labels.

AbbVie told BioCentury the U.S. labels for Viekira and Technivie now include a contraindication for patients with decompensated cirrhosis Child-Pugh class B and C. The label previously did not recommend Viekira for patients with decompensated cirrhosis Child-Pugh class B and was contraindicated in class C.

AbbVie also said Viekira's U.S. label now recommends that physicians evaluate evidence of hepatic decompensation prior to and during treatment in cirrhotic patients.

The agency reviewed AEs reported to the FDA Adverse Event Reporting System (FAERS) database and identified 26 cases of liver injury that were "possibly or probably" related to treatment with Viekira or Technivie. Ten patients experienced hepatic failure that led to liver transplantation or death, and 16 patients experienced varying degrees of liver dysfunction.

FDA said the majority of the reported AEs occurred in patients treated with Viekira who had evidence of advanced cirrhosis prior to starting treatment. Some cases of hepatic failure occurred in patients for whom the drugs are contraindicated or not recommended.

FDA approved Technivie in July in combination with ribavirin to treat non-cirrhotic adults with chronic HCV genotype 4 infection. The regimen includes ombitasvir, an HCV NS5A protein inhibitor; paritaprevir, an HCV NS3/4A protease inhibitor; and ritonavir, an HIV protease inhibitor. Paritaprevir is partnered with Enanta.

All three Technivie components are included in Viekira Pak, which also contains non-nucleoside HCV NS5B polymerase inhibitor dasabuvir. FDA approved Viekira last December with or without ribavirin to treat HCV genotype 1 infection in patients with or without compensated cirrhosis (see BioCentury Extra, July 24).

PBM Express Scripts Holding Co. Inc. (NASDAQ:ESRX) granted exclusive formulary status to Viekira last December in exchange for undisclosed rebates. Spokesperson David Whitrap told BioCentury the PBM will evaluate FDA's safety warning, but said that "at this point, we are not making any changes in our formulary" (see BioCentury Extra, Dec. 22, 2014).

AbbVie lost $9.2 billion in market cap Thursday, while Enanta shed $306 million.

Gilead Sciences Inc. (NASDAQ:GILD), which sells HCV therapies Harvoni ledipasvir/sofosbuvir and Sovaldi sofosbuvir, climbed $5.87 to $107.60 on Thursday, gaining $8.6 billion in market cap