U.S. PHARMACOPEIA

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Erythromycin and Benzoyl Peroxide Topical Gel
» Erythromycin and Benzoyl Peroxide Topical Gel is a mixture of Erythromycin in a suitable gel vehicle containing benzoyl peroxide and one or more suitable dispersants, stabilizers, and wetting agents. It contains not less than 90.0 percent and not more than 125.0 percent of the labeled amounts of erythromycin (C37H67NO13) and benzoyl peroxide (C14H10O4).
Packaging and storage— Before mixing, preserve the Erythromycin and the vehicle containing benzoyl peroxide in separate, tight containers. After mixing, preserve the mixture in tight containers.
Identification— Prepare Standard preparation and an Assay preparation as directed in the Assay, except to omit the Internal standard solution, and chromatograph as directed in the Assay: the Assay preparation exhibits a major peak for benzoyl peroxide, the retention time of which corresponds to that exhibited by the Standard preparation.
Minimum fill 755: meets the requirements.
Limit of benzoyl peroxide related substances—
Mobile phase A, Mobile phase B, Standard preparation A, Standard preparation B, Standard preparation C, Standard preparation D, Resolution solution, and Chromatographic system— Proceed as directed in the test for Related compounds under Benzoyl Peroxide Gel.
Test preparation— Transfer an accurately weighed quantity of Topical Gel, equivalent to about 100 mg of benzoyl peroxide, to a 50-mL volumetric flask, add 25 mL of acetonitrile, shake vigorously to disperse the specimen, sonicate for 5 minutes, dilute with acetonitrile to volume, mix, and filter.
Procedure— Proceed as directed for Procedure in the test for Related compounds under Benzoyl Peroxide Gel: it meets the limits stated.
Residual solvents 467: meets the requirements.
(Official January 1, 2007)
Assay for erythromycin— Proceed as directed for erythromycin under Antibiotics—Microbial Assays 81, using an accurately weighed portion of Topical Gel blended for 3 to 5 minutes in a high-speed glass blender jar containing 0.5 mL of polysorbate 80 and an accurately measured volume of Buffer No. 3 sufficient to obtain a stock solution having a convenient concentration of erythromycin. Dilute an accurately measured volume of this stock solution quantitatively with Buffer No. 3 to obtain a Test Dilution having a concentration of erythromycin assumed to be equal to the median dose level of the Standard.
Assay for benzoyl peroxide—
Mobile phase, Internal standard solution, Standard preparation, and Chromatographic system— Proceed as directed in the Assay under Benzoyl Peroxide Gel.
Assay preparation— Prepare as directed for Assay preparation in the Assay under Benzoyl Peroxide Gel, using Topical Gel.
Procedure— Proceed as directed for Procedure in the Assay under Benzoyl Peroxide Gel. Calculate the quantity, in mg, of benzoyl peroxide (C14H10O4) in the portion of Topical Gel taken by the formula:
125C(RU / RS),
in which C is the concentration, in mg per mL, of benzoyl peroxide in the Standard preparation, and RU and RS are the ratios of benzoyl peroxide peak response to ethyl benzoate peak response obtained from the Assay preparation and the Standard preparation, respectively.
Auxiliary Information— Staff Liaison : Brian D. Gilbert, Ph.D., Scientist
Expert Committee : (MDANT05) Monograph Development-Antibiotics
USP29–NF24 Page 834
Phone Number : 1-301-816-8223