» Digoxin Tablets contain not less than 90.0 percent and not more than 105.0 percent of the labeled amount of C41H64O14.
Packaging and storage Preserve in tight containers.
USP Reference standards 11
A: Chloramine Ttrichloroacetic acid reagentPrepare as directed for Identification test B under Digoxin Oral Solution.
Spotting solvent Use dehydrated alcohol.
Test solution Transfer an accurately weighed portion of finely powdered Tablets, equivalent to 0.5 mg of digoxin, to a 10-mL centrifuge tube. Add 2 mL of Spotting solvent, sonicate for 10 to 15 minutes, and centrifuge. Decant and use the supernatant.
Standard solution Dissolve an accurately weighed quantity of USP Digoxin RS in Spotting solvent to obtain a solution having a known concentration of about 0.25 mg per mL.
Procedure Proceed as directed for Procedure in the test for Related glycosides under Digoxin, except to omit the use of the Gitoxin standard solution. Examine the plate under long-wavelength UV light: the RF value of the principal spot obtained from the Test solution corresponds to that obtained from the Standard solution.
B: The retention time of the major peak in the chromatogram of the Assay preparation corresponds to that in the chromatogram of the Standard preparation, as obtained in the Assay.
Dissolution 711 [noteThroughout this procedure, use scrupulously clean glassware, which previously has been rinsed successively with hydrochloric acid, water, and alcohol, and carefully dried. Take precautions to prevent contamination from fluorescent particles and from metal and rubber surfaces. ]
Medium: 0.1 N hydrochloric acid; 500 mL. [noteUse the same batch of Dissolution Medium throughout the test. ]
Apparatus 1: 120 rpm.
Time: 60 minutes.
Ascorbic acidmethanol solution Prepare a solution containing 2 mg of ascorbic acid per mL of methanol.
Hydrogen peroxidemethanol solution On the day of use, dilute 2.0 mL of recently assayed 30 percent hydrogen peroxide with methanol to 100 mL. Store in a refrigerator. Just prior to use, dilute 2.0 mL of this solution with methanol to 100 mL.
Standard solutions Transfer about 25 mg of USP Digoxin RS, accurately weighed, to a 500-mL volumetric flask. Dissolve in a minimum amount of alcohol, add dilute alcohol (4 in 5) to volume, and mix. Dilute 10.0 mL of this solution with dilute alcohol (4 in 5) to 100.0 mL, and mix. Just prior to use, dilute suitable aliquots of the resulting solution with Dissolution Medium to 50.0 mL to prepare Standard solutions equivalent to 20%, 40%, 60%, 80%, and 100%, respectively, of the labeled amount of digoxin in 500 mL.
Test solution Promptly after withdrawal, pass a portion of the solution under test through a filter having a 0.8-µm or finer porosity, discarding the first 10 mL of the filtrate. This is the Test solution.
Procedure Transfer to individual glass-stoppered flasks duplicate 1.0-mL portions of the Test solution, 1.0-mL portions of each of the Standard solutions, and 1.0 mL of the Medium to provide a blank. Begin with the Standard solutions, and keep all flasks in the same sequence throughout, so that the elapsed time from addition of reagents to reading of fluorescence is the same for each flask in the set. Treating one flask at a time, add the following three reagents, in the order named, in as rapid a sequence as possible, swirling after each addition: 1.0 mL of Ascorbic acidmethanol solution, 5.0 mL of hydrochloric acid, and 1.0 mL of Hydrogen peroxidemethanol solution. Insert the stoppers in the flasks, and after 2 hours, measure the fluorescence at about 485 nm, the excitation wavelength being about 372 nm. To check the stability of the fluorometer, repeat the measurement of fluorescence on one or more treated Standard solutions. Correct each reading for the blank, and plot a standard curve of fluorescence versus percentage dissolution. Determine the percentage dissolution of digoxin in the Test solution by reading from the standard graph.
Tolerances Not less than 80% (Q) of the labeled amount of C41H64O14 is dissolved in 60 minutes. The requirement is met if the quantities dissolved from the Tablets tested conform to the accompanying acceptance table instead of the table shown under Dissolution 711.
Uniformity of dosage units 905: meet the requirements.
Mobile phase, Chromatographic system, and System suitability preparation Proceed as directed in the Assay under Digoxin.
Standard preparation Dissolve an accurately weighed quantity of USP Digoxin RS in diluted alcohol, and dilute quantitatively and stepwise with diluted alcohol to obtain a solution having a known concentration of about 40 µg per mL. Use a sonic bath to aid dissolution.
Assay preparation Weigh and finely powder not fewer than 20 Tablets. Transfer an accurately weighed portion of the powder, equivalent to about 1 mg of digoxin, to a glass-stoppered, 50-mL conical flask. Add 25.0 mL of diluted alcohol with swirling, sonicate for about 30 minutes, and cool. Filter a portion of this solution through a 0.8-µm porosity membrane filter, discarding the first 10 mL of the filtrate.
Procedure Separately inject equal volumes (about 50 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of C41H64O14 in the portion of Tablets taken by the formula:
25C(rU / rS)in which C is the concentration, in mg per mL, of USP Digoxin RS in the Standard preparation; and rU and rS are the responses for the digoxin peaks obtained from the Assay preparation and the Standard preparation, respectively.
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USP35NF30 Page 2906Pharmacopeial Forum: Volume No. 28(2) Page 281