Betamethasone Benzoate Gel

» Betamethasone Benzoate Gel contains an amount of betamethasone benzoate (C29H33FO6) equivalent to not less than 90.0 percent and not more than 110.0 percent of the labeled amount of betamethasone benzoate (C29H33FO6).

Packaging and storage— Preserve in tight containers. Store at 25

, excursions permitted between 15

and 30

. Protect from freezing.

USP Reference standards

—

USP Betamethasone Benzoate RS

USP Methyltestosterone RS

Identification— The retention time of the major peak in the chromatogram of the Assay preparation corresponds to that in the chromatogram of the Standard preparation, both relative to the internal standard, as obtained in the Assay.

Microbial enumeration tests

and Tests for specified microorganisms

— It meets the requirements of the tests for absence of Staphylococcus aureus and Pseudomonas aeruginosa.

Minimum fill

755

: meets the requirements.

Assay—

Mobile phase— Prepare a filtered and degassed mixture of methanol, water, and acetonitrile (23:18:9). Make adjustments if necessary (see System Suitability under Chromatography

621

Internal standard solution— Dissolve suitable quantities of USP Methyltestosterone RS in methanol to obtain a solution containing about 250 µg per mL.

Standard preparation— Dissolve an accurately weighed quantity of USP Betamethasone Benzoate RS in methanol, and dilute quantitatively, and stepwise if necessary, with methanol to obtain a solution having a known concentration of about 0.5 mg per mL. Transfer 5.0 mL of this solution to a 50-mL volumetric flask, add 10.0 mL of Internal standard solution, dilute with methanol to volume, and mix.

Assay preparation— Transfer an accurately weighed portion of Gel, equivalent to about 0.5 mg of betamethasone benzoate, to a 125-mL separatory funnel, add 20 mL of water and 2 mL of saturated sodium acetate solution, shake to disperse the Gel, add 2.0 mL of Internal standard solution, and mix. Extract this solution with one 50-mL portion of chloroform followed by three 40-mL portions of chloroform. Discard the aqueous layer. Wash the chloroform extract with 10 mL of water, allow to stand for 10 minutes, then pass through chloroform-wetted glass fiber filter paper and anhydrous sodium sulfate into a suitable container. Evaporate to dryness under vacuum at 30

. Dissolve the residue in 10 mL of methanol.

Chromatographic system (see Chromatography

621

)— The liquid chromatograph is equipped with a 236-nm detector and a 3.9-mm × 30-cm column that contains packing L1. The flow rate is about 1.5 mL per minute. The column temperature is maintained at 30

. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the relative retention times are about 1.33 for betamethasone benzoate and 1.0 for methyltestosterone; the resolution, R, between methyltestosterone and betamethasone benzoate is not less than 3.0; and the relative standard deviation for replicate injections is not more than 1.0%.

Procedure— Separately inject equal volumes (about 10 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of betamethasone benzoate (C29H33FO6) in the portion of Gel taken by the formula:

0.01C(RU / RS)

in which C is the concentration, in µg per mL, of USP Betamethasone Benzoate RS in the Standard preparation; and RU and RS are the ratios of the peak responses obtained for betamethasone benzoate and methyltestosterone from the Assay preparation and the Standard preparation, respectively.

Auxiliary Information— Please check for your question in the FAQs before contacting USP.

Topic/Question	Contact	Expert Committee
Monograph	Domenick Vicchio, Ph.D. Senior Scientific Liaison 1-301-998-6828	(SM42010) Monographs - Small Molecules 4
Reference Standards	RS Technical Services 1-301-816-8129 rstech@usp.org
61	Radhakrishna S Tirumalai, Ph.D. Principal Scientific Liaison 1-301-816-8339	(GCM2010) General Chapters - Microbiology
62	Radhakrishna S Tirumalai, Ph.D. Principal Scientific Liaison 1-301-816-8339	(GCM2010) General Chapters - Microbiology

USP35–NF30 Page 2340

Pharmacopeial Forum: Volume No. 29(5) Page 1428