Next-gen hepatitis C meds typically cure the disease with minimal side effects. But the FDA says it's tracking rare cases of liver damage, liver failure and death in patients using some top-selling drugs—mostly patients who shouldn't have been using the drugs in the first place.

The agency says it’s tracked 63 cases of worsening liver function in patients who took AbbVie’s Mavyret, Merck & Co’s Zepatier and Gilead Sciences' Vosevi. Some cases led to liver failure and death. 

That's a small fraction of the patients who've taken the drugs: 72,000 used them just last year, the agency said. Most of the patients involved shouldn't have been prescribed the medicines at all, because they already had suffered moderate to severe liver damage, the agency added. The drugs are approved to treat hep C only in patients with no or mild liver impairment. 

But in some of the cases FDA flagged, the patients had little to no liver impairment when they started therapy. There were other risk factors, however, the FDA noted, including cancer, alcohol abuse or diseases that can cause liver problems.

Among the meds listed in the FDA warning, AbbVie’s Mavyret—approved in August 2017—generated the most sales last year at $3.44 billion. Merck’s Zepatier, which hit the market before Mavyret, pulled in $455 million, while Gilead’s Vosevi generated $396 million. 

Altogether, the drugs "have been widely used and are safe and effective in patients without liver impairment or in those with mild liver impairment for whom they are indicated," the FDA said.

Doctors should continue prescribing the drugs as indicated and closely monitor patients for signs that their liver function may be worsening, the FDA said. Patients should remember that the cases are rare and to contact their doctors if they develop signs of liver injury.  

The alert highlights rare risks for a highly competitive drug class. Gilead once dominated the market with its hep C meds Sovaldi and Harvoni, but competition from AbbVie and others would later hurt its fortunes. In fact, the competition has grown so fierce in hep C that Gilead has taken the unusual move of launching authorized generics to its own drugs.

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