SAMARIUM SM-153 LEXIDRONAM

Samarium Sm-153 lexidronam is a medium energy beta-emitting radioisoto pe chelated to the tetraphosphate, ethylenediaminetetramethylenephosph onic acid (EDTMP). Sm-153 has a physical half-life of 1.9 days. Samari um Sm-153 lexidronam concentrates in bone tissue and has a metastatic lesion : normal bone ratio of 4. Clearance of nonskeletal radioactivit y after administration of samarium Sm-153 lexidronam is rapid, and is almost complete from the blood and urine within 1 and 6 hours, respect ively. Some degree of pain relief was achieved in 72% of patients with bone metastases after a single dose of samarium Sm-153 lexidronam 1 m Ci/kg (37 MBq/kg) compared with 44% of placebo recipients (p < 0.025). Relief was generally attained within 2 weeks and lasted for a median of 8 to 15 weeks. After recurrence of pain, a second dose of samarium Sm-153 lexidronam may produce further pain relief. in some patients. 1 53 The dose-limiting toxicity of samarium Sm-153 lexidronam is reversi ble myelosuppression.