» Liotrix Tablets contain not less than 90.0 percent and not more than 110.0 percent of the labeled amounts of Levothyroxine Sodium (C15H10I4NNaO4) and Liothyronine Sodium (C15H11I3NNaO4) in a ratio by weight of 4 to 1, respectively.
Packaging and storage Preserve in tight containers.
USP Reference standards 11
Identification The retention time of the two major peaks in the chromatogram of the Assay preparation corresponds to the levothyroxine and liothyronine peaks in the chromatogram of the Standard preparation, as obtained in the Assay.
Disintegration 701: 30 minutes.
Uniformity of dosage units 905: meet the requirements.
Mobile phase Prepare a filtered and degassed mixture of water and acetonitrile (65:35) that contains 2 mL of trifluoroacetic acid in each 1000 mL of solution. Make adjustments if necessary (see System Suitability under Chromatography 621).
0.01 M Methanolic sodium hydroxide Dissolve 400 mg of sodium hydroxide in 500 mL of water. Cool, add 500 mL of methanol, and mix.
Levothyroxine stock solution Dissolve an accurately weighed quantity of USP Levothyroxine RS in 0.01 M Methanolic sodium hydroxide to obtain a solution having a known concentration of about 0.4 mg of levothyroxine per mL.
Liothyronine stock solution Dissolve an accurately weighed quantity of USP Liothyronine RS in 0.01 M Methanolic sodium hydroxide to obtain a solution having a known concentration of about 0.4 mg of liothyronine per mL. Make a 1:10 dilution of this solution using Mobile phase.
Standard preparation Transfer appropriate volumes of Levothyroxine stock solution and Liothyronine stock solution to a suitable container, and dilute quantitatively and stepwise, if necessary, with Mobile phase to obtain a solution having known concentrations of about 10 µg of levothyroxine per mL and 2.5 µg of liothyronine per mL.
Assay preparation Transfer 20 Tablets to a 200-mL volumetric flask, add 180 mL of Mobile phase, and sonicate for 15 minutes, occasionally swirling the flask to accelerate the disintegration of the Tablets. Cool to room temperature, and dilute with Mobile phase to volume. Transfer a portion of the solution to a centrifuge tube, and centrifuge for 10 minutes at 5000 rpm. Quantitatively dilute a portion of the clear supernatant with Mobile phase to obtain concentrations of about 10.0 µg of levothyroxine sodium per mL and 2.5 µg of liothyronine sodium per mL.
Chromatographic system Proceed as directed in the Assay under Levothyroxine Sodium.
Procedure Proceed as directed for Procedure in the Assay under Levothyroxine Sodium. Calculate the quantity, in µg, of levothyroxine sodium (C15H10I4NNaO4) in the portion of Tablets taken by the formula:
(798.86/776.87)(10C)(rU / rS)in which 798.86 and 776.87 are the molecular weights of levothyroxine sodium and levothyroxine, respectively; C is the concentration, in µg per mL, of USP Levothyroxine RS in the Standard preparation; and rU and rS are the levothyroxine peak responses obtained from the Assay preparation and the Standard preparation, respectively.
Calculate the quantity, in µg of liothyronine sodium (C15H11I3NNaO4) in the portion of Tablets taken by the formula:
(672.96/650.98)(10C)(rU / rS)
in which 672.96 and 650.98 are the molecular weights of liothyronine sodium and liothyronine, respectively; C is the concentration, in µg per mL, of USP Liothyronine RS in the Standard preparation; and rU and rS are the liothyronine peak responses obtained from the Assay preparation and the Standard preparation, respectively.
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USP35NF30 Page 3693Pharmacopeial Forum: Volume No. 34(4) Page 955