The Food and Drug Administration approved a new hepatitis C drug from Vertex Pharmaceuticals Inc., marking the second such drug to be approved by the agency in less than two weeks after years without new treatments for the viral liver disease. Vertex's drug, called Incivek, joins Merck & Co.'s Victrelis. Both drugs have shown success in increasing the cure rates of the liver disease when added to current treatments, although Incivek has shown stronger effectiveness, simpler dosing and has a broader range of data. Although the drugs work in similar ways, it is difficult to directly compare different clinical studies, and no head-to-head trials of the two have been conducted. Hepatitis C is caused by a virus and can lead to liver failure, liver cancer and, in some cases, the need for a transplant. About 3.2 million Americans have the disease.