Dexamethasone Gel
»Dexamethasone Gel contains not less than 90.0percent and not more than 110.0percent of the labeled amount of C22H29FO5.
Packaging and storage— Preserve in collapsible tubes.Keep tightly closed.Avoid exposure to temperatures exceeding 30.
Identification— Evaporate 25mLof the Assay preparation,prepared as directed in the Assay,on a steam bath just to dryness,and dissolve the residue in 0.5mLof chloroform.The chloroform extract responds to the Thin-Layer Chromatographic Identification Test á201ñ,10µLof the chloroform extract and 10µLof a Standard solution containing about 500µg per mLof USP Dexamethasone RSbeing applied,and a mixture of chloroform and diethylamine (2:1)being used for development.Locate the spots on the plate by lightly spraying with dilute sulfuric acid (1in 2)and heating.
Minimum fill á755ñ: meets the requirements.
Assay—
Mobile solvent— Dilute 100mLof methylene chloride with isooctane to one liter.
Chromatographic columns— Tamp a pledget of glass wool at the constriction of a glass chromatographic tube measuring about 30-×1.5-cm,equipped with a polytef stopcock.Fill the tube about half-full with Mobile solvent.Mix 8g of chromatographic siliceous earth with 8mLof methanol and water (1:1).Transfer successive portions of the mixture to the column,emptying and adding Mobile solventafter each addition to pack the column.Finally drain the column to a layer of Mobile solventabout 1cm above the absorbant.Pack a second tube to provide a blank and proceed as directed for Assay preparation,but omit the specimen.
Standard preparation— Prepare a solution of USP Dexamethasone RSin alcohol to obtain a solution having a known concentration of about 10µg per mL.
Assay preparation— Accurately weigh an amount of Gel,equivalent to about 0.5mg of Dexamethasone in a 100-mLbeaker,add 1g of chromatographic siliceous earth,and mix.Transfer the mixture to the column,wash the beaker with small portions of Mobile solvent,adding them to the column.Adjust the flow rate to about 2mLper minute,discarding the eluate.Elute with four additional 25-mLportions of Mobile solvent,and discard.Rinse the sample beaker with two 25-mLportions of methylene chloride and transfer to the column,collecting the eluate in a suitable beaker.Elute the column with six additional 25-mLportions of methylene chloride,combining the eluates and evaporating with a gentle stream of air to dryness,dissolve the residue in alcohol,and transfer to a 50-mLvolumetric flask.Wash the beaker with successive 5-mLportions of alcohol,collecting the washings in the flask,dilute with alcohol to volume,and mix.Centrifuge or filter and then pipet 10mLof this solution,10mLof the Standard preparation,10mLof the column blank solution,and 10mLof alcohol to provide a reagent blank to separate flasks.Proceed as directed under Assay for Steroids á351ñ,except to allow to stand in the dark for 45minutes.Calculate the quantity,in mg,of C22H29FO5in the portion of Gel taken by the formula:
(0.05C)(AU-ACB/AS-ARB),
in which Cis the concentration,in µg per mL,of USP Dexamethasone RSin the Standard preparation;and AU,ACB,AS,and ARBare the absorbances of the solutions from the Assay preparation,column blank preparation,Standard preparation,and reagent blank preparation,respectively.
Auxiliary Information— Staff Liaison:Clydewyn M.Anthony,Ph.D.,Scientist
Expert Committee:(PA1)Pharmaceutical Analysis 1
USP28–NF23Page 589
Phone Number:1-301-816-8139