A: Ultraviolet Absorption 197U—

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.

Medium: methanol.

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.

100(ri / rS)

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.

Procedure— Proceed as directed for Procedure in the Assay under Rifabutin. Calculate the quantity, in mg, of C46H62N4O11 in the portion of Capsules taken by the formula: in which the terms are as defined therein.