Ethopabate
;)
Benzoic acid,4-(acetylamino)-2-ethoxy-,methyl ester.
Methyl 4-acetamido-2-ethoxybenzoate [59-06-03].
»Ethopabate contains not less than 96.0percent and not more than 101.0percent of C12H15NO4,calculated on the dried basis.
Packaging and storage—
Preserve in well-closed containers,protected from light.
Labeling—
Label it to indicate that it is for veterinary use only.
Identification—
A:
Infrared Absorption á197Mñ.
Solution:
10µg per mL.
Medium:
methanol.
Loss on drying á731ñ—
Dry 1.0g of it in vacuum at 60
for 2hours:it loses not more than 1.0%of its weight.
for 2hours:it loses not more than 1.0%of its weight.
Residue on ignition á281ñ:
not more than 0.5%.
Chromatographic purity—
Examine the chromatogram of the Assay preparation,as obtained in the Assay,for peaks that elute at the following retention times in relation to ethopabate:0.33,p-aminosalicylic acid (ethopabate related compound B);0.64,methyl 2-ethoxy-4-aminobenzoate (ethopabate related compound C);0.68,methyl 2-hydroxy-4-aminobenzoate (ethopabate related compound D);0.9,methyl 4-acetamido-2-hydroxybenzoate (ethopabate related compound A);and 1.6,ethyl 4-acetamido-2-ethoxybenzoate (ethopabate related compound E).Calculate the percentage of diazotizable substances,represented by peaks for ethopabate related compounds B,C,and D,if present,by the formula:
(0.72rB+0.68rC+0.74rD)/0.01rU,
in which 0.72,0.68,and 0.74are the response factors of ethopabate related compounds B,C,and D,respectively,relative to that of ethopabate,rB,rC,and rDare the responses of the peaks observed for ethopabate related compounds B,C,and D,respectively,and rUis the ethopabate peak response obtained from the Assay preparation:not more than 0.5%of diazotizable substances is found.Calculate the percentage of any other impurities by the formula:
100-AE-As,
in which AEis the percentage of total peak area represented by the main ethopabate peak in the chromatogram obtained from the Assay preparation,and Asis the percentage of peak area represented by the sum of the peaks for ethopabate related compounds B,C,and D:not more than 2.0%of other impurities is found.[NOTE—Exclude from the total peak area the responses of any minor peaks that are 0.01%or less than that of the main ethopabate peak.]
Assay—
Mobile phase—
Dissolve 3g of sodium 1-hexanesulfonate in 1liter of water,and adjust with phosphoric acid to a pHof 2.5.Prepare a filtered and degassed mixture of this solution,methanol,and acetonitrile (450:150:30).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).
Diluent—
Prepare a mixture of methanol and water (50:50).
Standard preparation—
Prepare a solution of USP Ethopabate RSin Diluenthaving a known concentration of about 0.4mg per mL.If necessary,filter this solution through a filter having a porosity of 0.5µm or finer,and use the filtrate as the Standard preparation.Use this solution on the day prepared.
Assay preparation—
Transfer about 40mg of Ethopabate,accurately weighed,to a 100-mLvolumetric flask,add about 80mLof Diluent,and dissolve with the aid of sonication.If necessary,filter this solution through a filter having a porosity of 0.5µm or finer,and use the filtrate as the Assay preparation.Use this solution on the day prepared.
Resolution solution—
Prepare a solution in Diluentcontaining about 0.4mg of USP Ethopabate RSand 0.1mg of USP Ethopabate Related Compound A RSper mL.
Chromatographic system
(see Chromatography á621ñ)—The liquid chromatograph is equipped with a 268-nm detector and a 3.9-mm ×30-cm column that contains packing L11and is maintained at about 40.The flow rate is about 1mLper minute.Chromatograph the Resolution solution,and record the peak responses as directed under Procedure:the relative retention times are about 0.9for methyl 4acetamido-2-hydroxybenzoate (ethopabate related compound A)and 1.0for ethopabate,the column efficiency is not less than 4000theoretical plates,the resolution,R,between the ethopabate related compound Apeak and the ethopabate peak is not less than 1.2,and the tailing factor is not more than 1.5.Chromatograph the Standard preparation,and record the peak responses as directed under Procedure:the relative standard deviation for replicate injections is not more than 1.0%.
.The flow rate is about 1mLper minute.Chromatograph the Resolution solution,and record the peak responses as directed under Procedure:the relative retention times are about 0.9for methyl 4acetamido-2-hydroxybenzoate (ethopabate related compound A)and 1.0for ethopabate,the column efficiency is not less than 4000theoretical plates,the resolution,R,between the ethopabate related compound Apeak and the ethopabate peak is not less than 1.2,and the tailing factor is not more than 1.5.Chromatograph the Standard preparation,and record the peak responses as directed under Procedure:the relative standard deviation for replicate injections is not more than 1.0%.
Procedure—
Separately inject equal volumes (about 10µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the areas of the responses for the major peaks.Calculate the quantity,in mg,of C12H15NO4in the portion of Ethopabate taken by the formula:
100C(rU/rS),
in which Cis the concentration,in mg per mL,of USP Ethopabate RSin the Standard preparation,and rUand rSare the ethopabate peak responses obtained from the Assay preparationand the Standard preparation,respectively.
Auxiliary Information—
Staff Liaison:Ian DeVeau,Ph.D.,Senior Scientist
Expert Committee:(VET)Veterinary Drugs
USP28–NF23Page 791
Phone Number:1-301-816-8178