Betamethasone Sodium Phosphate 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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Betamethasone Sodium Phosphate Injection is a sterile solution of Betamethasone Sodium Phosphate in Water for Injection. It contains an amount of betamethasone sodium phosphate (C₂₂H₂₈FNa₂O₈P) equivalent to not less than 90.0 percent and not more than 110.0 percent of the labeled amount of betamethasone (C₂₂H₂₆FO₅).

Packaging and storage-Preserve in single-dose or in multiple-dose containers, preferably of Type I glass.

USP REFERENCE STANDARDS (11)

USP Betamethasone Sodium Phosphate RS

1 Identification

Dilute the Injection with methanol, if necessary, to obtain a solution containing about 2 mg of betamethasone sodium phosphate per mL Separately apply 10 µL of this test solution and 10 µL of a solution of USP Betamethasone Sodium Phosphate RS in methanol containing 2 mg per mL to a thin-layer chromatographic plate (see Chromatography (621)) coated with chromatographic silica gel mixture. Develop the chromatogram in an equilibrated chamber containing n-butyl alcohol previously shaken with 1 N hydrochloric acid, until the solvent front has moved about three-fourths of the length of the plate. Remove the plate from the developing chamber, air-dry, then spray with a mixture of sulfuric acid, methanol, and nitric acid (10:10:1). Heat the plate at 105° for 10 minutes: the R_F value of the principal spot from the test solution corresponds to that obtained from the Standard solution.

BACTERIAL ENDOTOXINS TEST (85) It contains not more than 29.2 USP Endotoxin Units per mg of betamethasone.

PH (791): between 8.0 and 9.0.

PARTICULATE MATTER IN INJECTIONS (788): meets the requirements for small-volume injections.

Other requirements-It meets the requirements under Injections and Implanted Drug Products (1).

2 Assay

Mobile phase-Prepare a filtered and degassed mixture of methanol and 0.05 M monobasic potassium phosphate (1:1). Make adjustments if necessary (see System Suitability under Chromatography (621)).

Internal standard solution-Transfer about 100 mg of butylparaben to a 100-ml volumetric flask, add methanol to volume, and mix.

Standard preparation-Using an accurately weighed quantity of USP Betamethasone Sodium Phosphate RS, prepare a solution in water containing 4 mg per mL. Transfer 3.0 mL of this solution to a 25-mL volumetric flask, add 5.0 mL of Internal standard solution, dilute with water to volume, and mix to obtain a solution having a known concentration of about 0.5 mg of USP Betamethasone Sodium Phosphate RS per mL.

Assay preparation-Transfer an accurately measured volume of Injection, equivalent to about 9 mg of betamethasone, to a 25-mL volumetric flask. Add 5.0 mL of the Internal standard solution, dilute with water to volume, and mix.

Chromatographic system (see Chromatography (621))-The liquid chromatograph is equipped with a 254-nm detector and a 3.9-mm x 30-cm column that contains packing L1. The flow rate is about 2 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the resolution, R, between the analyte and internal standard peaks is not less than 5; and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure-Separately inject equal volumes (about 20 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. The relative retention times are about 2.4 for butylparaben and 1.0 for betamethasone sodium phosphate. Calculate the quantity, in mg, of C₂₂H₂₆FO₅ in each mL of the Injection taken by the formula:

(392.47/516.41)(25C/V)(R_u /R_s )

in which 392.47 and 516.41 are the molecular weights of betamethasone and betamethasone sodium phosphate, respectively, C is the concentration, in mg per mL, of USP Betamethasone Sodium Phosphate RS in the Standard preparation; V is the volume, in mL, of Injection taken; and R_u and R_s are the peak response ratios obtained from the Assay preparation and the Standard preparation, respectively.