About 250,000 patients took direct-acting antivirals in 2015. Since launching Sovaldi in 2013 and Harvoni in 2014, Gilead has reaped billions in sales at a breakneck pace as the meds lifted the company's fortunes for several quarters along the way. But more recently, a slowdown has left analysts and investors puzzled and waiting to see where the company will look for its next big move. The findings come on the heels of an FDA decision last fall to slap a black-box warning on the class, alerting patients and docs of the potential for a return of hep B infection in current or previous hep B patients. That represented the first major safety issue for the drugs, ISMP noted, and couldn't have been "detected in clinical testing ... because such patients were excluded."