Patients that shouldn’t have taken the drugs got sicker, and some died.

The U.S. Food and Drug Administration tracks adverse events using its FDA Adverse Event Reporting System (FAERS). Based on recent reports of patients taking one of three newer hepatitis C medications getting sicker, the agency has issued a safety warning.

The three drugs are AbbVie's Mavyret (glecaprevir/pibrentasvir), Merck & Co.'s Zepatier (sofosbuvir/velpatasvir)‎ and Gilead's Vosevi (ofosbuvir/velpatasvir/voxilaprevir). The first two are combination oral therapies containing a hepatitis C virus (HCV) NS5A inhibitor and a hepatitis C virus NS3/4A protease inhibitor. The latter is a triple-combination therapy that also contains a nucleotide analog NS5B polymerase inhibitor. All are approved to treat adults with hepatitis C who have not developed liver impairment or have mild liver impairment

The majority of reports (46) were linked to Mavyret, with far fewer associated with Zepatier (14) and Vosevi (3). In most of the reported cases, the patients had more advanced liver damage or other liver problems and should not have been prescribed the medication. In most instances, the symptoms had resolved or liver health was improving at the time the safety warning was issued. The patients with the most severe liver damage, however, experienced liver failure and death.

The FDA’s safety warning stresses the importance of prescribing these three drugs to the appropriate patients. The agency noted that the drugs "have been widely used and are safe and effective in patients with no or mild liver impairment." To prevent problems from progressing if an error has been made, the FDA recommends close monitoring of liver function for all patients taking Mavyret, Zepatier or Vosevi. Patients taking these drugs are also asked to report symptoms including fatigue, nausea, or yellowing of the eyes or skin.