for solid packaged in single-unit containers: meets the requirements for Content Uniformity with respect to ampicillin and probenecid.

Standard preparation— Prepare as directed for Standard Preparation under Iodometric Assay—Antibiotics 425, using USP Ampicillin RS.

Assay preparation— Constitute Ampicillin and Probenecid for Oral Suspension as directed in the labeling, and mix. Transfer the resulting suspension to a high-speed glass blender jar containing sufficient water to make 500.0 mL, and blend for about 10 minutes. Quantitatively dilute an accurately measured volume of this stock solution with water to obtain an Assay preparation containing about 1.25 mg of ampicillin per mL.

Procedure— Proceed as directed for Procedure under Iodometric Assay—Antibiotics 425. Calculate the quantity, in mg, of ampicillin (C16H19N3O4S) in the Ampicillin and Probenecid for Oral Suspension taken by the formula: in which L is the labeled quantity, in mg, of ampicillin in the Ampicillin and Probenecid for Oral Suspension; and D is the concentration, in mg per mL, of ampicillin in the Assay preparation on the basis of the labeled quantity in the Ampicillin and Probenecid for Oral Suspension and the extent of dilution.

Standard preparation— Dissolve an accurately weighed portion of USP Probenecid RS in sodium carbonate solution (1 in 100) to obtain a solution having a known concentration of about 1 mg per mL.

Assay preparation— Constitute Ampicillin and Probenecid for Oral Suspension as directed in the labeling, and mix. Quantitatively dilute the resulting suspension with sodium carbonate solution (1 in 100) to obtain a solution containing about 1 mg of probenecid per mL, mix, and filter.

Procedure— Transfer 2.0 mL of the clear Assay preparation to a 125-mL separator, and add 8.0 mL of 1.0 N hydrochloric acid. Extract this solution with four 20-mL portions of chloroform, filtering each extract through a glass wool pledget and 6 g of chloroform-washed anhydrous sodium sulfate into a 100-mL volumetric flask. Wash the pledget and the sodium sulfate with chloroform, collecting the washings in the 100-mL volumetric flask, dilute with chloroform to volume, and mix. Treat 2.0 mL of the Standard preparation in the same manner. Concomitantly determine the absorbances of the solutions from the Assay preparation and the Standard preparation at the wavelength of maximum absorbance at about 257 nm, with a suitable spectrophotometer, using chloroform washed with sodium carbonate solution (1 in 100) as the blank. Calculate the quantity, in mg, of probenecid (C13H19NO4S) in the Ampicillin and Probenecid for Oral Suspension taken by the formula: in which C is the concentration, in mg per mL, of USP Probenecid RS in the Standard preparation; L is the labeled quantity, in mg, of probenecid in the Ampicillin and Probenecid for Oral Suspension; D is the concentration, in mg per mL, of probenecid in the Assay preparation on the basis of the labeled quantity in the Ampicillin and Probenecid for Oral Suspension and the extent of dilution; and AU and AS are the absorbances of the solutions from the Assay preparation and the Standard preparation, respectively.