Michael Erman U.S. and European drug regulators said on Friday they are reviewing the safety of the widely taken heartburn drug ranitidine, commonly known by the brand name Zantac, after they found traces of a probable cancer-causing impurity in some versions of the medicine. The U.S. Food and Drug Administration said it had found traces of the impurity, called N-nitrosodimethylamine (NDMA), in some of drugs with ranitidine in them. Both the FDA and the European Medicines Agency said they will review the drug's safety, but neither agency is currently calling for patients to stop taking it. The impurity in ranitidine was first flagged to the regulators by Valisure, an online pharmacy that tests the medication it sells for flaws. Valisure said in its report that it found the impurity in both Sanofi SA's branded Zantac as well as generic versions of the drug. But the FDA would not confirm in which versions of the drug it had found the impurity, noting that it found quite different - and lower - amounts of NDMA in the drugs.