Anticoagulant action of rare earth metals

Some of the lanthanides, the rare earth metals, lanthanum (La), cerium (Ce), neodymium (Nd), samarium (Sm), terbium (Tb), dysprosium (Dy), erbium (Er) and ytterbium (Yb) prolonged the clotting time of normal human plasma in a dose-dependent manner when clotting was induced either by thromboplastin or by kaolin in the presence of cephalin and Ca2+. They also prolonged the activated factor X induced clotting time of platelet-rich plasma. The amidolytic activities of activated factor X and thrombin progressively decreased with increasing amount of rare earth metals. These results suggested that the rare earth metals appear to show their anticoagulant effect with mechanisms in part the inhibition of the enzymatic activities of both activated factor X and thrombin.