A: It responds to Identification test A under Rifampin Capsules, the test solution being prepared by dissolving the contents of a container in chloroform to obtain a solution containing about 10 mg of rifampin per mL.

B: The retention time of the rifampin peak in the chromatogram of the Assay preparation corresponds to that in the chromatogram of the Standard preparation as obtained in the Assay.

(Official January 1, 2007)

Phosphate buffer, Mobile phase, Solvent mixture, Standard preparation, Resolution solution, and Chromatographic system— Prepare as directed in the Assay under Rifampin.

Assay preparation 1 (where it is represented as being in a single-dose container)—Constitute a container of Rifampin for Injection in a volume of water, accurately measured, corresponding to the volume of diluent specified in the labeling. [NOTE—Use this solution within 2 hours.] Withdraw all of the withdrawable contents, using a suitable hypodermic needle and syringe, and transfer to a suitable volumetric flask of such capacity that when diluted with acetonitrile to volume, a solution is obtained containing about 6 mg of rifampin (C43H58N4O12) per mL. [NOTE—Use this stock solution within 5 hours.] Dilute an accurately measured volume of this stock solution quantitatively and stepwise with Solvent mixture to obtain a solution having a concentration of about 0.02 mg of rifampin per mL. [NOTE—Prepare this final dilution immediately prior to injection into the chromatograph.]

Assay preparation 2 (where the label states the quantity of rifampin in a given volume of constituted solution)—Constitute a container of Rifampin for Injection in a volume of water, accurately measured, equivalent to the volume of diluent specified in the labeling. [NOTE—Use this solution within 2 hours.] Dilute an accurately measured volume of the constituted solution quantitatively and stepwise with acetonitrile to obtain a solution having a concentration of about 0.2 mg of rifampin (C43H58N4O12) per mL. [NOTE—Use this stock solution within 5 hours.] Transfer 10.0 mL of this solution to a 100-mL volumetric flask, dilute with Solvent mixture to volume, and mix. [NOTE—Prepare this final dilution immediately prior to the injection into the chromatogram.]

Procedure— Proceed as directed for Procedure in the Assay under Rifampin. Calculate the quantity, in mg, of rifampin (C43H58N4O12) withdrawn from the container of constituted Rifampin for Injection, or in the volume of constituted Rifampin for Injection taken by the formula: in which L is the labeled quantity, in mg, of rifampin in the container, or in the volume of constituted solution taken, D is the concentration, in mg per mL, of rifampin in Assay preparation 1 or in Assay preparation 2, on the basis of the labeled quantity in the container, or in the volume of constituted solution taken, and the extent of dilution, C is the concentration, in mg per mL, calculated on the dried basis, of USP Rifampin RS in the Standard preparation, and rU and rS are the rifampin peak responses obtained from Assay preparation 1, or Assay preparation 2, and the Standard preparation, respectively.