0.1 M Sodium acetate buffer— Transfer 13.61 g of sodium acetate trihydrate to a 1-L volumetric flask, add water to dissolve, dilute with water to volume, and mix. Adjust with 0.1 M acetic acid to a pH of 5.0.

Medium: 0.1 M Sodium acetate buffer; 900 mL.

Apparatus 2: 50 rpm.

Time: 30 minutes.

Procedure— Determine the amount of clarithromycin (C38H69NO13) dissolved in the Medium, as directed in the Assay, using instead of the Assay preparation a filtered portion of the solution under test quantitatively diluted with Mobile phase to yield a test solution containing about 125 µg of clarithromycin per mL. Calculate the quantity, in mg, of clarithromycin dissolved by the formula: in which D is the appropriate dilution factor used to prepare the test solution, and the other terms are as defined therein.

Tolerances— Not less than 80% (Q) of the labeled amount of clarithromycin (C38H69NO13) is dissolved in 30 minutes.

Mobile phase— Prepare a mixture of methanol and 0.067 M monobasic potassium phosphate (650:350), adjust with phosphoric acid to a pH of 4.0, pass through a filter having a 0.5-µm or finer porosity, and degas. Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard preparation— Dissolve an accurately weighed quantity of USP Clarithromycin RS in methanol, shaking and sonicating if necessary to effect dissolution, to obtain a stock solution having a known concentration of about 625 µg of clarithromycin (C38H69NO13) per mL, taking into account the stated potency, in µg per mg, of USP Clarithromycin RS. Transfer 10.0 mL of this stock solution to a 50-mL volumetric flask, dilute with Mobile phase to volume, and mix. Pass through a filter having a 0.5-µm or finer porosity, and use the filtrate as the Standard preparation. This solution contains about 125 µg of clarithromycin (C38H69NO13) per mL.

Resolution solution— Prepare a solution of USP Clarithromycin Related Compound A RS in methanol containing about 625 µg per mL. Transfer 10 mL of this solution and 10 mL of the stock solution used to prepare the Standard preparation to a 50-mL volumetric flask, dilute with Mobile phase to volume, and mix.

Assay preparation— Finely powder an accurately counted number of Tablets, equivalent to about 2000 mg of clarithromycin, and with the aid of methanol quantitatively transfer the powder to a 500-mL volumetric flask, add about 350 mL of methanol, and shake by mechanical means for 30 minutes. Dilute with methanol to volume, mix, and allow any insoluble matter to settle. Transfer 3.0 mL of the supernatant to a 100-mL volumetric flask, dilute with Mobile phase to volume, and mix. Pass a portion of this solution through a filter having a 0.5-µm or finer porosity, and use the filtrate as the Assay preparation.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 210-nm detector, an optional guard column that contains packing L1, and a 4.6-mm × 15-cm column that contains packing LI. The chromatograph is maintained at a constant temperature of about 50. The flow rate is about 1 mL per minute. Chromatograph the Resolution solution, and record the responses as directed for Procedure: the relative retention times are about 0.75 for clarithromycin and 1.0 for clarithromycin related compound A; and the resolution, R, between clarithromycin and clarithromycin related compound A is not less than 2.0. Chromatograph the Standard preparation, and record the responses as directed for Procedure: the column efficiency, determined from the clarithromycin peak, is not less than 750 theoretical plates when calculated by the formula: the tailing factor is not less than 0.9 and not more than 1.5; and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 20 to 50 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the areas for the major peaks. Calculate the quantity, in mg, of clarithromycin (C38H69NO13) in each Tablet taken by the formula: in which C is the concentration, in µg per mL, of clarithromycin (C38H69NO13) in the Standard preparation; N is the number of Tablets taken; and rU and rS are the clarithromycin peak responses obtained from the Assay preparation and the Standard preparation, respectively.