Thyroid Tablets »Thyroid Tablets contain not less than 90.0percent and not more than 110.0percent of the labeled amounts of levothyroxine and liothyronine,the labeled amounts being 38µg of levothyroxine and 9µg of liothyronine for each 65mg of the labeled content of thyroid. Packaging and storage— Preserve in tight containers. USP Reference standards á11ñ USP Liothyronine RS.USP Levothyroxine RS. Microbial limits á61ñ Tablets meet the requirements of the tests for absence of Salmonellaspecies and Escherichia coli. Disintegration á701ñ: 15minutes,with disks. Uniformity of dosage units á905ñ: meet the requirements,the following procedure being used where the test for Content Uniformityis required. PROCEDUREFOR CONTENT UNIFORMITY Standard solution— Accurately weigh 1.69g of potassium iodate,and transfer to a 1-liter volumetric flask.Dissolve in about 200mLof water,dilute with water to volume,and mix.This is a stock solution having a concentration of about 1mg per mLwith respect to iodine.Pipet 8mLof the stock solution into a 250-mLvolumetric flask,dilute with water to volume,and mix.Transfer an appropriate aliquot,based on dosage being analyzed (i.e.,¼gr,1mL;½gr,2mL;1gr,4mL;1½gr,6mL;2gr,8mL;2½gr,10mL;3gr,12mL;4gr,16mL;5gr,20mL),to a 100-mLvolumetric flask containing 8g of potassium carbonate dissolved in 70mLof water.Add 1mLof bromine TS,mix,add sufficient sodium sulfite (about 20mg)until the solution becomes colorless,and mix.Dilute with water to volume,and mix. Test solution— Crush 1Tablet 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 4g of anhydrous potassium carbonate,mix carefully,and gently tap the crucible several times to compact the mixture.Overlay with 4g more of anhydrous potassium carbonate,and again compact the material thoroughly by tapping.Place the crucible in a preheated muffle furnace,and ignite at 675to 700for 25minutes.Cool,add 30mLof water,carefully heat on a hot plate to dissolve the residue,and filter through a funnel with a glass wool plug into a 100-mLvolumetric flask.Repeat the heating and filtration with two additional 30-mLportions of water,and add these filtrates to the volumetric flask.Add 1mLof bromine TS,mix,add sufficient sodium sulfite (about 20mg)until the solution becomes colorless,and mix.Dilute with water to volume,and mix. Blank solution— Prepare a reagent blank by putting 8g of anhydrous potassium carbonate into a 100-mLvolumetric flask and dissolving it in 70mLof water,add 1mLof freshly prepared bromine TS,mix,add sufficient sodium sulfite (about 20mg)until the solution becomes colorless,dilute with water to volume,and mix to obtain the Blank solution. Procedure— Transfer 10mLof the Test solutionto a dry polarographic cell.Bubble nitrogen through the solution for 5minutes,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 -0.8Vto -1.5Vat the rate of 5mVper second,and 50-mVpulses.Record the polarogram of the Test solution,the Standard solution,and the Blank solution.At the peaks near -1.18Vin the polarograms obtained from the Standard solutionand the Test solutionmeasure 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 126.90and 214.00are the atomic weight of iodine (I)and the molecular weight of potassium iodate (KIO3),respectively;Vis the volume,in mL,of the aliquot portion of potassium iodate solution used to prepare the Standard Solution;andPHUand PHSare the peak heights obtained from the Test solutionand the Standard solution,respectively.Proceed as directed for Content Uniformity á905ñ,using the results obtained by this procedure to determine the total iodine content of individual Tablets,and use the Assay preparationto 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 Assayunder Thyroid. Assay preparation— Weigh and finely powder not less than 20Tablets.Using an accurately weighed portion of the powder,proceed as directed for Assay preparationin the Assayunder Thyroid,beginning with “equivalent to about 38µg of levothyroxine.” Auxiliary Information— Staff Liaison:Larry N.Callahan,Ph.D.,Scientist Expert Committee:(BNT)Biotechnology and Natural Therapeutics/Diagnostics USP28–NF23Page 1924 Pharmacopeial Forum:Volume No.28(1)Page 88 Phone Number:1-301-816-8385