Dibucaine Cream

» Dibucaine Cream contains not less than 90.0 percent and not more than 110.0 percent of the labeled amount of dibucaine (C20H29N3O2) in a suitable cream base.

Packaging and storage— Preserve in collapsible tubes or in tight, light-resistant containers.

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USP Dibucaine Hydrochloride 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, 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 and Chromatographic system— Proceed as directed in the Assay under Dibucaine.

Standard preparation— Dissolve an accurately weighed quantity of USP Dibucaine Hydrochloride RS in an amount of 0.1 N hydrochloric acid equivalent to 20% of the flask's volume, and dilute quantitatively, and stepwise if necessary, with methanol to obtain a solution having a known concentration of about 0.25 mg per mL.

Assay preparation— Weigh accurately a portion of Cream, equivalent to about 22 mg of dibucaine, transfer to a separator containing 25 mL of ether, and mix to dissolve. Extract successively with two 9-mL portions of 0.1 N hydrochloric acid, combining the extracts in a 100-mL volumetric flask. Extract the ether phase in the separator with 2 mL of water, collecting the aqueous extract in the 100-mL volumetric flask. Dilute with methanol to volume, and mix. Pass through a suitable filter having a 0.5-µm or finer porosity.

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 area responses for the major peaks. Calculate the quantity, in mg, of dibucaine (C20H29N3O2) in the portion of Cream taken by the formula:

(343.46/379.93)(100C)(rU / rS)

in which 343.46 and 379.93 are the molecular weights of dibucaine and dibucaine hydrochloride, respectively; C is the concentration, in mg per mL, of USP Dibucaine Hydrochloride RS in the Standard preparation; and rU and rS are the area responses of the dibucaine peaks obtained 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 2874

Pharmacopeial Forum: Volume No. 31(2) Page 399