Methenamine Tablets
»Methenamine Tablets contain not less than 95.0percent and not more than 105.0percent of the labeled amount of methenamine (C6H12N4).
Packaging and storage— Preserve in well-closed containers.
Identification— Dissolve about 500mg of powdered Tablets in 10mLof water,add 10mLof 2Nsulfuric acid,and heat:formaldehyde is liberated,recognizable by its odor and by its darkening of paper moistened with silver ammonium nitrate TS.On the subsequent addition of an excess of 1Nsodium hydroxide to the solution,ammonia is evolved.
Dissolution,Procedure for a Pooled Sample á711ñ—
Medium: water;900mL.
Apparatus 1: 100rpm.
Time: 45minutes.
Procedure— Determine the amount of C6H12N4dissolved,employing the procedure set forth in theAssay,making any necessary modifications.
Tolerances— Not less than 75%(Q)of the labeled amount of C6H12N4is dissolved in 45minutes.
Uniformity of dosage units á905ñ: meet the requirements.
Assay—
Chromotropic acid solutionand Standard preparation— Prepare as directed in theAssay underMethenamine Elixir(Oral Solution,official June 1,2005).
Assay preparation— Weigh and finely powder not fewer than 20Tablets.Transfer an accurately weighed portion of the powder,equivalent to about 500mg of methenamine,to a 250-mLvolumetric flask,dilute with water to volume,mix,and filter,discarding the first 20mLof the filtrate.Transfer 25.0mLof the subsequent filtrate to a 1000-mLvolumetric flask,dilute with water to volume,and mix.Proceed as directed forAssay preparation in theAssay underMethenamine Elixir(Oral Solution,official June 1,2005),beginning with “Transfer a 2.0-mLportion of this stock solution.”
Procedure— Proceed as directed forProcedure in theAssay underMethenamine Elixir (Oral Solution,official June 1,2005).Calculate the quantity,in mg,of methenamine (C6H12N4)in the portion of Tablets taken by the formula:
500C[(AU-BU)/(AS-BS)],
in whichCis the concentration,in µg per mL,of USP Methenamine RSin theStandard preparation;and AU,AS,BU,and BSare as defined therein.
Auxiliary Information— Staff Liaison:Behnam Davani,Ph.D.,MBA,Senior Scientist
Expert Committee:(PA7)Pharmaceutical Analysis 7
USP28–NF23Page 1242
Pharmacopeial Forum:Volume No.30(1)Page 130
Phone Number:1-301-816-8394