Samarium SM-153 lexidronam is a chelated complex of a radioisotope of the element samarium with ethylenediamine tetra(methylene phosphonic acid) (EDTMP). Samarium Sm-153 EDTMP has an affinity for bone and concentrates in areas of bone turnover in association with hydroxyapatite. In clinical studies employing planar imaging techniques, more Samarium (153Sm) lexidronam accumulates in osteoblastic lesions than in normal bone with a lesion-to-normal bone ratio of approximately 5. It is indicated for the relief of pain in patients with confirmed osteoblastic metastatic bone lesions that enhance on radionuclide bone scan. It should not be given concurrently with chemotherapy or external beam radiation therapy unless the benefit outweighs the risks. The most common adverse events are: nausea and vomiting, hemoglobin decrease, myasthenia, paresthesia, thrombocytopenia and abdominal pain.