» Rifabutin Capsules contain not less than 90.0 percent and not more than 110.0 percent of the labeled amount of C46H62N4O11.
Packaging and storage Preserve in well-closed containers, protected from light and from excessive heat.
USP Reference standards 11
Solution Prepare the test solution as follows. Suspend a quantity of Capsule contents, equivalent to about 200 mg of rifabutin, in 20 mL of methanol, sonicate for about 5 minutes, and filter through a 0.5-µm or finer porosity filter. Dilute a portion of the filtrate quantitatively, and stepwise if necessary, with methanol to obtain a solution having a concentration of about 20 µg per mL. Prepare a Standard solution by dissolving a quantity of USP Rifabutin RS in methanol, with the aid of sonication, to obtain a solution having a concentration of about 20 µg per mL, and filter through a 0.5-µm or finer porosity filter.
B: The retention time of the major peak in the chromatogram of the Assay preparation corresponds to that in the chromatogram of the Standard preparation obtained as directed in the Assay.
Medium: 0.01 N hydrochloric acid; 900 mL.
Apparatus 1: 100 rpm.
Time: 45 minutes.
Procedure Determine the amount of C46H62N4O11 dissolved from UV absorbances at the wavelength of maximum absorbance at about 280 nm of filtered portions of the solution under test, suitably diluted with Dissolution Medium, in comparison with a Standard solution having a known concentration of USP Rifabutin RS in the same medium, taking into account its designated potency.
Tolerances Not less than 75% (Q) of the labeled amount of C46H62N4O11 is dissolved in 45 minutes.
Chromatographic purity Using the chromatogram of the Assay preparation obtained as directed in the Assay, calculate the percentage of impurities by the formula:
100(ri / rS)in which ri is the response of an individual impurity and rS is the sum of the responses of all peaks: any impurity peak detected at a retention time of about 0.5, 0.6, 0.8, or 1.4 relative to the retention time of the rifabutin peak does not exceed 1.0%, not more than 0.5% of any other impurity is detected, and the total of all impurity peaks is not more than 4.5%.
0.1 M Monobasic potassium phosphate, Mobile phase, Standard preparation, Resolution solution, and Chromatographic system Proceed as directed in the Assay under Rifabutin.
Assay preparation Remove as completely as possible the contents of not less than 20 Capsules, weigh accurately, and determine the average weight of the Capsule contents. Transfer an accurately weighed portion of the powder, equivalent to about 25 mg of rifabutin, to a 50-mL volumetric flask. Add 5 mL of acetonitrile, dilute with Mobile phase to volume, and mix. Filter through a 0.5-µm or finer porosity filter, and use the filtrate as the Assay preparation.
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USP35NF30 Page 4550