Benzocaine Ointment
» Benzocaine Ointment contains not less than 90.0 percent and not more than 110.0 percent of the labeled amount of C9H11NO2 in a suitable ointment base.
Packaging and storage— Preserve in tight containers, protected from light, and avoid prolonged exposure to temperatures exceeding 30.
Identification—
Ointments having water-soluble bases— Transfer an amount of Ointment, equivalent to about 5 mg of benzocaine, to a small beaker, add 20 mL of 0.5 N hydrochloric acid, warm gently to disperse the Ointment, cool, and filter, if necessary. To 10 mL of the filtrate add 5 drops of a solution of sodium nitrite (1 in 10) and 2 drops of methyl red TS, and neutralize with 1 N sodium hydroxide. Add 2 mL of a solution of 100 mg of 2-naphthol in 5 mL of sodium hydroxide TS: an orange-red precipitate is formed.
Ointments having water-insoluble bases— Transfer an amount of Ointment, equivalent to about 2.5 mg of benzocaine, to a small separator, and dissolve in 20 mL of ether. Extract with 10 mL of 0.5 N hydrochloric acid, and filter the aqueous phase through paper into a small beaker. Add 5 drops of a solution of sodium nitrite (1 in 10) and 2 drops of methyl red TS, and neutralize with 1 N sodium hydroxide. Add 2 mL of a solution of 100 mg of 2-naphthol in 5 mL of 1 N sodium hydroxide: an orange-red precipitate is formed.
Microbial enumeration tests 61 and Tests for specified microorganisms 62— It meets the requirements of the tests for absence of Staphylococcus aureus and Pseudomonas aeruginosa.
Minimum fill 755: meets the requirements.
Assay—
Ointments having water-soluble bases— Accurately weigh an amount of Ointment, equivalent to about 200 mg of benzocaine, in a tared 250-mL beaker. Add 50 mL of water and 5 mL of hydrochloric acid, and stir by mechanical means until solution is effected. Cool the solution in an ice bath to about 10, and titrate slowly with 0.1 M sodium nitrite VS, determining the endpoint potentiometrically using a calomel-platinum electrode system. Perform a blank determination, and make any necessary correction. Each mL of 0.1 M sodium nitrite is equivalent to 16.52 mg of C9H11NO2.
Ointments having water-insoluble bases— Accurately weigh an amount of Ointment, equivalent to about 200 mg of benzocaine, and transfer to a 125-mL separator. Suspend the Ointment in 50 mL of ether by shaking, and extract with three successive 25-mL portions of 1 N hydrochloric acid, filtering each portion into a 250-mL beaker, and proceed as directed under Ointments having water-soluble bases, beginning with “Cool the solution.”
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Topic/Question Contact Expert Committee
Monograph Domenick Vicchio, Ph.D.
Senior Scientific Liaison
1-301-998-6828		 (SM42010) Monographs - Small Molecules 4
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 2321