Thyroid Tablets

» Thyroid Tablets contain not less than 90.0 percent and not more than 110.0 percent of the labeled amounts of levothyroxine and liothyronine, the labeled amounts being 38 µg of levothyroxine and 9 µg of liothyronine for each 65 mg of the labeled content of thyroid.

Packaging and storage— Preserve in tight containers.

—

USP Liothyronine RS

USP Levothyroxine RS

Microbial enumeration tests

and Tests for specified microorganisms

— Tablets meet the requirements of the tests for absence of Salmonella species and Escherichia coli.

Disintegration

701

: 15 minutes, with disks.

Uniformity of dosage units

905

: meet the requirements, the following procedure being used where the test for Content Uniformity is required.

Procedure for content uniformity—

Standard solution— Accurately weigh 1.69 g of potassium iodate, and transfer to a 1-liter volumetric flask. Dissolve in about 200 mL of water, dilute with water to volume, and mix. This is a stock solution having a concentration of about 1 mg per mL with respect to iodine. Pipet 8 mL of the stock solution into a 250-mL volumetric flask, dilute with water to volume, and mix. Transfer an appropriate aliquot, based on dosage being analyzed (i.e., ¼ gr, 1 mL; ½ gr, 2 mL; 1 gr, 4 mL; 1½ gr, 6 mL; 2 gr, 8 mL; 2½ gr, 10 mL; 3 gr, 12 mL; 4 gr, 16 mL; 5 gr, 20 mL), to a 100-mL volumetric flask containing 8 g of potassium carbonate dissolved in 70 mL of water. Add 1 mL of bromine TS, mix, add sufficient sodium sulfite (about 20 mg) until the solution becomes colorless, and mix. Dilute with water to volume, and mix.

Test solution— Crush 1 Tablet in a porcelain crucible with a glass rod. Remove any sample adhering to the glass rod with a spatula, and add it to the crucible. Add 4 g of anhydrous potassium carbonate, mix carefully, and gently tap the crucible several times to compact the mixture. Overlay with 4 g more of anhydrous potassium carbonate, and again compact the material thoroughly by tapping. Place the crucible in a preheated muffle furnace, and ignite at 675

to 700

for 25 minutes. Cool, add 30 mL of water, carefully heat on a hot plate to dissolve the residue, and filter through a funnel with a glass wool plug into a 100-mL volumetric flask. Repeat the heating and filtration with two additional 30-mL portions of water, and add these filtrates to the volumetric flask. Add 1 mL of bromine TS, mix, add sufficient sodium sulfite (about 20 mg) until the solution becomes colorless, and mix. Dilute with water to volume, and mix.

Blank solution— Prepare a reagent blank by putting 8 g of anhydrous potassium carbonate into a 100-mL volumetric flask and dissolving it in 70 mL of water, add 1 mL of freshly prepared bromine TS, mix, add sufficient sodium sulfite (about 20 mg) until the solution becomes colorless, dilute with water to volume, and mix to obtain the Blank solution.

Procedure— Transfer 10 mL of the Test solution to a dry polarographic cell. Bubble nitrogen through the solution for 5 minutes, and then direct the stream of nitrogen above the solution. Use a suitable differential pulse polarograph equipped with a saturated calomel reference electrode and a dropping mercury electrode with a 1-second drop time. Scan from

0.8V to

1.5V at the rate of 5 mV per second, and 50-mV pulses. Record the polarogram of the Test solution, the Standard solution, and the Blank solution. At the peaks near

1.18V in the polarograms obtained from the Standard solution and the Test solution measure the heights from the baseline, as established by the Blank solution. Calculate the amount of iodine, in µg, in the Tablet taken by the formula:

(126.90 / 214.00)(54.08V)(PHU / PHS)

in which 126.90 and 214.00 are the atomic weight of iodine (I) and the molecular weight of potassium iodate (KIO3), respectively; V is the volume, in mL, of the aliquot portion of potassium iodate solution used to prepare the Standard Solution; and PHU and PHS are the peak heights obtained from the Test solution and the Standard solution, respectively. Proceed as directed for Content Uniformity

905

, using the results obtained by this procedure to determine the total iodine content of individual Tablets, and use the Assay preparation to perform the composite determination for iodine. The requirement is met if the amount of iodine in each Tablet is within the range of 85.0% to 115% of the composite assay for iodine with a relative standard deviation of not more than 6.0%.

Assay—

Mobile phase, Reducing buffer solution, Proteolytic enzyme, Enzyme deactivating solution, Standard preparation, Chromatographic system, and Procedure— Proceed as directed in the Assay under Thyroid.

Assay preparation— Weigh and finely powder not less than 20 Tablets. Using an accurately weighed portion of the powder, proceed as directed for Assay preparation in the Assay under Thyroid, beginning with “equivalent to about 38 µg of levothyroxine.”

Auxiliary Information— Please check for your question in the FAQs before contacting USP.

Topic/Question	Contact	Expert Committee
Monograph	Thomas A. Sigambris, M.S. Scientific Liaison 1-301-998-6789	(BIO12010) Monographs - Biologics and Biotechnology 1
Reference Standards	RS Technical Services 1-301-816-8129 rstech@usp.org
61	Radhakrishna S Tirumalai, Ph.D. Principal Scientific Liaison 1-301-816-8339	(GCM2010) General Chapters - Microbiology
62	Radhakrishna S Tirumalai, Ph.D. Principal Scientific Liaison 1-301-816-8339	(GCM2010) General Chapters - Microbiology
701	Margareth R.C. Marques, Ph.D. Senior Scientific Liaison 1-301-816-8106	(GCDF2010) General Chapters - Dosage Forms

USP35–NF30 Page 4856

Pharmacopeial Forum: Volume No. 28(1) Page 88