Tobramycin Ophthalmic Ointment »Tobramycin Ophthalmic Ointment contains the equivalent of not less than 90.0percent and not more than 120.0percent of the labeled amount of tobramycin (C18H37N5O9). Packaging and storage— Preserve in collapsible ophthalmic ointment tubes. USP Reference standards á11ñ USP Tobramycin RS. Identification— Vigorously shake by mechanical means a quantity of Ophthalmic Ointment,equivalent to about 3mg of tobramycin,with 2mLof chloroform.Add 1mLof water,shake vigorously by mechanical means for 1minute,and centrifuge for 15minutes:the clear upper,aqueous layer so obtained meets the requirements of Identificationtest Aunder Tobramycin. Sterility á71ñ It meets the requirements when tested as directed for Membrane Filtrationunder Test for Sterility of the Product to be Examined.. Minimum fill á755ñ: meets the requirements. Water,Method Iá921ñ: not more than 1.0%,20mLof a mixture of toluene and methanol (7:3)being used in place of methanol in the titration vessel. Metal particles á751ñ: meets the requirements. Assay— Mobile phase,2,4-Dinitrofluorobenzene reagent,Tris(hydroxymethyl)aminomethane reagent,Standard preparation,Resolution solution,and Chromatographic system— Proceed as directed in the Assayunder Tobramycin. Assay preparation— Transfer an accurately weighed portion of Ophthalmic Ointment,equivalent to about 4.5mg of tobramycin,to a separator,add 50mLof ether,and extract with four 20-to 25-mLportions of water.Combine the water extracts in a 100-mLvolumetric flask,dilute with water to volume,and mix. Derivatization procedure— Proceed as directed in the Assayunder Tobramycin,except to use 15.0mLof Assay preparationinstead of 4.0mL. Procedure— Proceed as directed in the Assayunder Tobramycin.Calculate the quantity of tobramycin (C18H37N5O9),in mg,in the portion of Ophthalmic Ointment taken by the formula: (4/150)(CE)(rU/rS), in which the terms are as defined therein. Auxiliary Information— Staff Liaison:William W.Wright,Ph.D.,Scientific Fellow Expert Committee:(PA7)Pharmaceutical Analysis 7 USP28–NF23Page 1940 Phone Number:1-301-816-8335