Samarium Sm 153 Lexidronam Injection

This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition

Issued and maintained by the United States Pharmacopeial Convention (USP)

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» Samarium Sm 153 Lexidronam Injection is a sterile aqueous solution suitable for intravenous injection that contains 153Sm in the form of a complex with ethylenediaminetetramethylenephosphonic acid (EDTMP). It contains not less than 90.0 percent and not more than 110.0 percent of the labeled amount of 153Sm expressed in megabecquerels per mL (or in millicuries per mL) at the date and time indicated in the labeling. Not less than 99 percent of the Sm-153 is complexed by EDTMP. It contains no antimicrobial agents.

Packaging and storage— Preserve in adequately shielded single-dose containers in a freezer.

1 Labeling—

Label it to include the following, in addition to the information specified for Labeling 〈7〉, Labels and Labeling for Injectable Products:

the time and date of calibration;

the amount of 153Sm complexed with EDTMP expressed as total megabecquerels (or millicuries) and the concentration as megabecquerels per mL (or millicuries per mL) at the time of calibration;

the expiration date and time;

the statement “Caution—Radioactive Material.”

Labeling indicates that:

— dosage calculations must correct for radioactive decay;

— the radioactive half-life of 153Sm is 46.3 hours;

— it should not be diluted or mixed with other solutions;

— it must be thawed at room temperature before administration;

— it must be used within 8 hours of thawing.

Radionuclide identification 〈821〉—

Samarium-153 decays by beta emission to stable Europium 153 as follows:

640 keV (30%)

710 keV (50%)

810 keV (20%)

Average emission energy: 233 keV.

Its gamma-ray spectrum matches that of a known-purity specimen of 153Sm that exhibits major photopeaks at 70 keV and 103 keV.

Bacterial Endotoxins Test 〈85〉—

Limit: NMT 175/V EU per mL, where V = maximum recommended total dose (mL) at expiration time.

pH 〈791〉:

Between 7.0 and 8.5.

Radionuclidic purity 〈821〉—

Using a gamma-ray spectrophotometer, determine radionuclidic purity:

• NLT 99.8% of total radioactivity is Sm 153 at expiry.

• Europium 154 ≤ 3.44 kBq per 37 MBq (or 0.0093% of total Sm 153 at expiry).

• Sum of all other radionuclidic impurities ≤ 0.1907% of total Sm 153 at expiry.

Radiochemical purity 〈821〉—

2 Mobile phase—

To a 1-L volumetric flask add:

• 8.0 g sodium chloride

• 0.2 g monobasic potassium phosphate

• 1.15 g dibasic sodium phosphate

• 0.2 g potassium chloride

Dilute with distilled water to volume; mix.

Adjust if necessary (see System Suitability under Chromatography 〈621〉).

Chromatographic system—

Glass column: 10 mm × 40 mm

Packed by gravity flow with strong cation-exchange resin*

(prepare resin by mixing 5 g resin + 25 mL water → use 0.5 mL final resin volume)

3 Procedure—

Place packed column into an ion-chamber dose counter to measure background Sm 153.

Apply ~10 µL Injection to column → record total radioactivity.

Elute complexed radioactivity with ~20 mL Mobile phase → record retained radioactivity.

Subtract background radioactivity from all values.

Calculate % complexed radioactivity:

100(T − S/0.95) / T

T = total radioactivity

S = free Sm-153 retained on column

0.95 = correction factor (5% uncomplexed Sm-153 passes through)

Acceptance: NLT 99% of Sm-153 is complexed by EDTMP.

* Sephadex-CM C-25 ion exchange resin (Aldrich Chemical No. 27, 124-1).

Other requirements—

Meets requirements of Injections and Implanted Drug Products 〈1〉;

Not subject to Container content.

Assay for radioactivity (Radioactivity 〈821〉)—

Using a calibrated counting system, determine MBq (or mCi) per mL.

Activity must be within ±10% of labeled amount at calibration time.