Federal health officials are warning doctors and patients that two hepatitis C drugs from AbbVie can cause life-threatening liver injury in patients with advanced forms of the disease. The Food and Drug Administration said Thursday it will require AbbVie to add new warnings to Viekira Pak and Technivie after reported deaths and liver transplants in patients who already had liver damage caused by hepatitis C. The warning could reshape the growing field of high-priced drugs to treat the virus, which also includes Gilead Sciences' blockbuster medications Sovaldi and Harvoni.