(Official January 1, 2007)

pH 6.8 buffer, Mobile phase, Imipenem standard preparation, Cilastatin standard preparation, and Chromatographic system— Prepare as directed in the Assay under Imipenem and Cilastatin for Injection.

Assay preparation— Constitute Imipenem and Cilastatin for Injectable Suspension in a volume of saline TS, accurately measured, corresponding to the volume of solvent specified in the labeling. Withdraw all of the withdrawable contents, using a suitable hypodermic needle and syringe, and dilute quantitatively with saline TS to obtain a stock solution containing about 2500 µg of imipenem per mL. Transfer 10.0 mL of this solution to a 50-mL volumetric flask, dilute with pH 6.8 buffer to volume, and mix.

Procedure— Separately inject equal volumes (about 10 µL) of the Imipenem standard preparation, the Cilastatin standard preparation, and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantities, in mg, of anhydrous imipenem (C12H17N3O4S) and cilastatin (C16H26N2O5S) withdrawn from the container taken by the formula: in which C is the concentration, in mg per mL, of USP Imipenem Monohydrate RS or USP Cilastatin Ammonium Salt RS in the appropriate Standard preparation, P is the content, in µg per mg, of anhydrous imipenem (C12H17N3O4S) or cilastatin (C16H26N2O5S) in the relevant Reference Standard, L is the labeled quantity, in mg, of imipenem or cilastatin in the container, D is the concentration, in µg per mL, of imipenem or cilastatin in the Assay preparation based on the labeled quantity in the container and the extent of dilution, and rU and rS are the peak responses of the corresponding analyte obtained from the Assay preparation and the appropriate Standard preparation, respectively.