Methimazole Tablets
»Methimazole Tablets contain not less than 94.0percent and not more than 106.0percent of the labeled amount of methimazole (C4H6N2S).
Packaging and storage— Preserve in well-closed,light-resistant containers.
Identification— Digest a quantity of powdered Tablets,equivalent to about 10mg of methimazole,with 10mLof warm chloroform for 20minutes,filter,and evaporate the filtrate on a steam bath to dryness:the residue responds to the Identificationtests under Methimazole.
Dissolution á711ñ—
Medium: water;500mL.
Apparatus 1: 100rpm.
Time: 30minutes.
Procedure— Determine the amount of C4H6N2Sdissolved from UVabsorbances at the wavelength of maximum absorbance at about 252nm of filtered portions of the solution under test,suitably diluted with Medium,if necessary,in comparison with a Standard solution having a known concentration of USP Methimazole RSin the same Medium.
Tolerances— Not less than 80%(Q)of the labeled amount of C4H6N2Sis dissolved in 30minutes.
Uniformity of dosage units á905ñ: meet the requirements.
Procedure for content uniformity— Place 1Tablet,previously crushed or finely powdered,in a 100-mLvolumetric flask,add 50mLof water,and shake by mechanical means for 30minutes.Dilute with water to volume,mix,and filter,discarding the first 20mLof filtrate.Dilute a portion of the subsequent filtrate quantitatively and stepwise with water so that the assumed concentration of methimazole is about 5µg per mL.Dissolve an accurately weighed quantity of USP Methimazole RSin water,and dilute quantitatively and stepwise with water to obtain a Standard solution having a known concentration of about 5µg per mL.Concomitantly determine the absorbances of both solutions in 1-cm cells at the wavelength of maximum absorbance at about 252nm,with a suitable spectrophotometer,using water as the blank.Calculate the quantity,in mg,of methimazole (C4H6N2S)in the Tablet taken by the formula:
(T/5)C(AU/AS),
in which Tis the labeled quantity,in mg,of methimazole in the Tablet;Cis the concentration,in µg per mL,of USP Methimazole RSin the Standard solution;and AUand ASare the absorbances of the solution from the Tablet and the Standard solution,respectively.
Assay— Weigh and finely powder not fewer than 20Tablets.Weigh accurately a portion of the powder,equivalent to about 120mg of methimazole,and place in a 100-mLvolumetric flask.Add about 80mLof water,insert the stopper,and shake by mechanical means or occasionally by hand during 30minutes.Dilute with water to volume,and mix.Filter,and transfer 50.0mLof the filtrate to a 125-mLconical flask.Add from a buret 3.5mLof 0.1Nsodium hydroxide VS,mix,and add,with agitation,about 7mLof 0.1Nsilver nitrate.Add 1mLof bromothymol blue TS,and continue the titration with the 0.1Nsodium hydroxide VSuntil a permanent,blue-green color is produced.Each mLof 0.1Nsodium hydroxide is equivalent to 11.42mg of C4H6N2S.
Auxiliary Information— Staff Liaison:Elena Gonikberg,Ph.D.,Scientist
Expert Committee:(PA4)Pharmaceutical Analysis 4
USP28–NF23Page 1244
Phone Number:1-301-816-8251