Ethosuximide Oral Solution, chemical structure, molecular formula, Reference Standards

Ethosuximide Oral Solution

»Ethosuximide Oral Solution contains not less than 90.0percent and not more than 105.0percent of the labeled amount of ethosuximide (C7H11NO2).

Packaging and storage— Preserve in tight containers.

USP Reference standards á11ñ— USP Ethosuximide RS.

Identification—

A: Infrared Absorption á197Sñ—

Spectral range: 3000cm–1to 1650cm–1.

Test solution— Transfer a portion of Oral Solution,equivalent to 150mg of ethosuximide,to a 125-mLseparatory funnel,add 50mLof ether,and shake well.Allow the layers to separate,and retain the ether layer.Wash the ether layer with three 10-mLportions of water.Transfer the ether layer to a suitable beaker,add 5g of anhydrous sodium sulfate,and swirl.Filter the mixture into a 50-mLvolumetric flask through a small pledget of cotton that has been previously washed with ether.Evaporate to dryness.Dissolve the residue in 5mLof chloroform.

Standard solution— Dissolve 150mg of USP Ethosuximide RSin 5.0mLof chloroform.

B: The retention time of the major peak in the chromatogram of the Assay preparationcorresponds to that in the chromatogram of the Standard preparation,as obtained in the Assay.

pHá791ñ: between 4.5and 5.8.

Limit of 2-ethyl-2-methylsuccinic acid—

Mobile phase,System suitability solution,and Chromatographic system— Proceed as directed in the Assayunder Ethosuximide Capsules.

Standard solution— Dissolve an accurately weighed quantity of 2-ethyl-2-methylsuccinic acid in Mobile phase,and dilute quantitatively,and stepwise if necessary,to obtain a solution having a known concentration of about 0.05mg per mL.

Test solution— Using a “to contain”pipet,transfer a volume of Oral Solution,equivalent to 250mg of ethosuximide,to a 100-mLvolumetric flask.Rinse the pipet several times with Mobile phase,dilute with Mobile phaseto volume,and mix.

Procedure— Separately inject equal volumes (about 10µL)of the Standard solutionand the Test solutioninto the chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the percentage of 2-ethyl-2-methylsuccinic acid,in relation to the quantity of ethosuximide,in the volume of Oral Solution taken by the formula:

40C(rU/rS),

in which Cis the concentration,in mg per mL,of 2-ethyl-2-methylsuccinic acid in the Standard solution;and rUand rSare the peak responses for 2-ethyl-2-methylsuccinic acid obtained from the Test solutionand the Standard solution,respectively:not more than 2.0%is found.

Assay—

Mobile phase,System suitability solution,Standard preparation,and Chromatographic system— Proceed as directed in the Assayunder Ethosuximide Capsules.

Assay preparation— Transfer an accurately measured volume of Oral Solution,equivalent to about 250mg of ethosuximide,to a 100-mLvolumetric flask.Dilute with Mobile phaseto volume,and mix.Transfer 5.0mLof this solution to a 200-mLvolumetric flask,dilute with Mobile phaseto volume,and mix.

Procedure— Separately inject equal volumes (about 10µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the quantity,in mg,of ethosuximide (C7H11NO2)in the volume of Oral Solution taken by the formula:

4000C(rU/rS),

in which Cis the concentration,in mg per mL,of USP Ethosuximide RSin the Standard preparation;and rUand rSare the ethosuximide peak responses obtained from the Assay preparationand the Standard preparation,respectively.

Auxiliary Information— Staff Liaison:Salvador C.Salado,M.S.,Scientist and Latin American Liaison

Expert Committee:(PA3)Pharmaceutical Analysis 3

USP28–NF23Page 793

Pharmacopeial Forum:Volume No.28(5)Page 1407

Phone Number:1-301-816-8165