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

B: The retention time of the rifampin peak in the chromatogram of the Assay preparationcorresponds to that in the chromatogram of the Standard preparationas obtained in the Assay.

Phosphate buffer,Mobile phase,Solvent mixture,Standard preparation,Resolution solution,andChromatographic system— Prepare as directed in the Assayunder 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 2hours.]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 6mg of rifampin (C43H58N4O12)per mL.[NOTE—Use this stock solution within 5hours.]Dilute an accurately measured volume of this stock solution quantitatively and stepwise with Solvent mixtureto obtain a solution having a concentration of about 0.02mg 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 2hours.]Dilute an accurately measured volume of the constituted solution quantitatively and stepwise with acetonitrile to obtain a solution having a concentration of about 0.2mg of rifampin (C43H58N4O12)per mL.[NOTE—Use this stock solution within 5hours.]Transfer 10.0mLof this solution to a 100-mLvolumetric flask,dilute with Solvent mixtureto volume,and mix.[NOTE—Prepare this final dilution immediately prior to the injection into the chromatogram.]

Procedure— Proceed as directed for Procedurein the Assayunder Rifampin.Calculate the quantity,in mg,of rifampin (C43H58N4O12)withdrawn from the container of constituted Rifampin for Injection,or in the volume of constituted Rifampin for Injection taken by the formula: in which Lis the labeled quantity,in mg,of rifampin in the container,or in the volume of constituted solution taken,Dis the concentration,in mg per mL,of rifampin in Assay preparation 1or 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,Cis the concentration,in mg per mL,calculated on the dried basis,of USP Rifampin RSin the Standard preparation,and rUand rSare the rifampin peak responses obtained from Assay preparation 1,or Assay preparation 2,and the Standard preparation,respectively.