QUADRAMET- samarium sm-153 lexidronam pentasodium injection, solution
EUSA Pharma (USA), Inc.
QUADRAMET® is a therapeutic agent consisting of radioactive samarium and a tetraphosphonate chelator, ethylenediaminetetramethylenephosphonic acid (EDTMP). QUADRAMET® is formulated as a sterile, non-pyrogenic, clear, colorless to light amber isotonic solution of samarium-153 lexidronam for intravenous administration. QUADRAMET® does not contain a preservative.
Each milliliter contains 35 mg EDTMP•H2 O, 5.3 mg Ca [as Ca(OH)2 ], 14.1 mg Na [as NaOH], equivalent to 44 mg Ca/Na EDTMP (anhydrous calc.), 5-46 µg samarium (specific activity of approximately 1.0-11.0 mCi/µg Sm), and 1850 ± 185 MBq (50 ± 5 mCi) of samarium-153 at calibration.
The structural formula of samarium lexidronam pentasodium is:
The ionic formula is 153 Sm+3 [CH2 N(CH2 PO3 -2)2 ]2 and the ionic formula weight is 581.1 daltons (pentasodium form, 696).
The pH of the solution is 7.0 to 8.5.
QUADRAMET® is supplied frozen in single-dose glass vials containing 3 mL with 5550 MBq (150 mCi) of samarium-153 at calibration.
Samarium-153 is produced in high yield and purity by neutron irradiation of isotopically enriched samarium Sm 152 oxide (152 Sm2 O3 ). It emits both medium-energy beta particles and a gamma photon, and has a physical half-life of 46.3 hours (1.93 days). Samarium-153 has average and maximum beta particle ranges in water of 0.5 mm and 3.0 mm, respectively. The primary radiation emissions of samarium-153 are shown in Table 1.
* Maximum energies are listed for the beta emissions, the average beta particle energy is 233 keV.
The specific gamma-ray constant for samarium-153 is 0.46 R/mCi-hr at 1 cm (1.24×10-5 mSv/MBq- hr at 1 Meter). The half-value thickness of lead (Pb) for samarium-153 is approximately 0.10 mm. The use of 1 mm of lead will decrease the external radiation exposure by a factor of approximately 1,000. QUADRAMET® should be stored in a lead-shielded container and frozen until use.
Radioactive decay factors to be applied to the stated value for radioactive concentration at calibration are given in Table 2. All radioactivity is calibrated to the reference date and time on the vial.
* Time = hours before (-) or after (+) calibration
QUADRAMET® (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 QUADRAMET® accumulates in osteoblastic lesions than in normal bone with a lesion-to-normal bone ratio of approximately 5. The mechanism of action of QUADRAMET® in relieving the pain of bone metastases is not known.
Human protein binding has not been studied; however, in dog, rat and bovine studies, less than 0.5% of samarium-153 EDTMP is bound to protein. At physiologic pH, >90% of the complex is present as 153 Sm[EDTMP]-5 , and <10% as 153 SmH[EDTMP]-4. The octanol/ water partition coefficient is <10-5.
The greater the number of metastatic lesions, the more skeletal uptake of Sm-153 radioactivity. The relationship between skeletal uptake and the size of the metastatic lesions has not been studied. The total skeletal uptake of radioactivity was 65.5%± 15.5% of the injected dose in 453 patients with metastatic lesions from a variety of primary malignancies. In a study of 22 patients with a wide range in the number of metastatic sites, the % of the injected dose (% ID) taken up by bone ranged from 56.3% in a patient with 5 metastatic lesions to 76.7% in a patient with 52 metastatic lesions. If the number of metastatic lesions is fixed, over the range 0.1 to 3.0 mCi/kg, the % ID taken up by bone is the same regardless of the dose.
The complex formed by samarium and EDTMP is excreted as an intact, single species that consists of one atom of the Sm-153 and one molecule of the EDTMP, as shown by an analysis of urine samples from patients (n=5) administered samarium Sm-153 EDTMP. Metabolic products of samarium Sm-153 EDTMP were not detected in humans.
For QUADRAMET® , calculations of the % ID detected in the whole body, urine and blood were corrected for radionuclide decay. The clearance of activity through the urine is expressed as the cumulated activity excreted. The whole body retention is the simple reciprocal of the cumulated urine activity. (See Skeletal Uptake Section).
Blood: Clearance of radioactivity from the blood demonstrated biexponential kinetics after intravenous injection in 19 patients (10 men, 9 women) with a variety of primary cancers that were metastatic to bone. Over the first 30 minutes, the radioactivity (mean ± SD) in the blood decreased to 15% (±8%) of the injected dose with a t 1/2 of 5.5 min (±1.1 min). After 30 minutes, the radioactivity cleared from the blood more slowly with a t1/2 of 65.4 min (± 9.6 min). Less than 1% of the dose injected remained in the blood 5 hr after injection.
Urine: Samarium Sm-153 EDTMP radioactivity was excreted in the urine after intravenous injection. During the first 6 hours, 34.5% (±15.5%) was excreted. Overall, the greater the number of metastatic lesions, the less radioactivity was excreted.
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