Chemical formula: C₆H₁₂N₂Na₅O₁₂P₄Sm Molecular mass: 586.021 g/mol PubChem compound: 76962714
Samarium has an affinity for skeletal tissue and concentrates in areas of bone turnover in intimate association with hydroxyapatite.
Studies in rats have demonstrated that samarium is cleared rapidly from the blood and localises to growing areas of bone matrix, specifically the layer of osteoid undergoing mineralisation.
Total skeletal uptake of samarium in studies of 453 patients with a variety of primary malignancies was 65.5 ± 15.5 % of the administered activity. A positive correlation was found between skeletal uptake and the number of metastatic sites. In contrast, skeletal uptake was inversely proportional to plasma radioactivity at 30 minutes.
In patients, samarium is rapidly cleared from the blood. Thirty minutes after injection of the agent to 22 patients, only 9.6 ± 2.8 % of the administered activity remained in plasma. At 4 and 24 hours, plasma radioactivity had decreased from 1.3 ± 0.7 % to 0.05 ± 0.03 %.
Urinary excretion occurred predominantly during the first 4 hours (30.3 ± 13.5 %). At 12 hours, 35.3 ± 13.6 % of the administered activity had been excreted into the urine. Less urinary excretion occurred in patients who had extensive bony metastases, regardless of the amount of radiopharmaceutical administered.
Analysis of urine samples found the radioactivity to be present as the intact complex
The radiolysis products of Sm-EDTMP showed a renal toxicity in rats and dogs with a no effect level of 2.5 mg/kg.
Repeated dose administration of samarium (153Sm)-EDTMP to dogs indicated a slightly longer time for depressed bone marrow and peripheral haematological parameters to recover when compared to recovery following only single dose administration.
Radioactive Sm-EDTMP has not been tested for mutagenicity/carcinogenicity but due to the radiation dose resulting from therapeutic exposure it should be regarded as presenting a genotoxic/carcinogenic risk.
Non-radioactive Sm-EDTMP showed no mutagenic potential in a battery of in vivo and in vitro tests. The same results were observed for Sm-EDTMP enriched with radiolysis degradants.
In a carcinogenic potential study of EDTMP, osteosarcomas occurred in rats at high doses. In the absence of genotoxic properties, these effects can be assigned to the EDTMP chelatant properties leading to osseous metabolism disturbances.
No studies have been performed to assess the effect of samarium on reproduction.
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