NEW YORK (AP) — Schering-Plough Corp. said Thursday its experimental pill for hepatitis C helped reduce the virus in twice as many patients as existing treatments, though it also was associated with a mild form of anemia. The company reported midstage results of its pill boceprevir to treat the most virulent form of the hepatitis C virus. When the pill was added to currently used drugs about 75 percent of patients saw their virus drop to undetectable levels. That was nearly double the 38 percent response rate of patients who received only drugs currently on the market. Despite those positive effects, Schering also reported a likely association between patients who saw a reduction in their hepatitis levels and anemia, a blood disorder that causes weakness and fatigue. The company stressed that anemia is a common side effect of treatment with the standard of care hepatitis drugs given to patients. About 30 percent of patients taking only older drugs reported anemia, compared with more than 40 percent of those who also took boceprevir. Along with anemia, the most common side effects were fatigue, nausea and headache. Kenilworth, N.J.-based Schering released the results of the 595-patient study at a European meeting of liver specialists held in Denmark. Competitors working on rival hepatitis C treatments include Vertex Pharmaceuticals, Pfizer and Anadys Pharmaceuticals Inc.