Carbidopa and Levodopa Tablets
»Carbidopa and Levodopa Tablets contain not less than 90.0percent and not more than 110.0percent of the labeled amounts of carbidopa (C10H14N2O4)and of levodopa (C9H11NO4).
Packaging and storage— Preserve in well-closed,light-resistant containers.
Identification— Transfer a portion of powdered Tablets,equivalent to about 10mg of carbidopa,to a 100-mLvolumetric flask containing about 50mLof 0.05Nhydrochloric acid.Agitate for 20minutes,add methanol to volume,mix,and filter or centrifuge.Separately prepare 2Standard solutions containing 0.1mg per mLof USP Carbidopa RSand USP Levodopa RS,respectively,in a solvent prepared by mixing equal volumes of 0.05Nhydrochloric acid and methanol.Apply 20µLof the test solution and 20µLof each Standard solution at separate points to a thin-layer chromatographic plate (see Chromatography á621ñ)coated with a 0.25-mm layer of chromatographic silica gel.Develop the chromatogram using a solvent system consisting of a mixture of acetone,chloroform,n-butanol,glacial acetic acid,and water (60:40:40:40:35)until the solvent front has moved about 15cm.Air-dry,spray uniformly with about 0.5mLof ninhydrin reagent (prepared by dissolving 0.3g of ninhydrin in 100mLof n-butanol acidified with 3mLof glacial acetic acid),and heat at 105for about 10minutes:the solution under test exhibits two spots (reddish brown for levodopa and yellow-orange for carbidopa)having RFvalues that correspond to those exhibited by the Standard solutions.
Dissolution á711ñ—
Medium: 0.1Nhydrochloric acid;750mL.
Apparatus 1: 50rpm.
Time: 30minutes.
Procedure— Determine the amounts of carbidopa and levodopa in solution in filtered portions of the solution under test,in comparison with a Standard solution having known concentrations of USP Carbidopa RSand USP Levodopa RSin the same medium,as directed for Procedurein the Assay.
Tolerances— Not less than 80%(Q)of the labeled amounts of carbidopa (C10H14N2O4)and levodopa (C9H11NO4)is dissolved in 30minutes.
Uniformity of dosage units á905ñ: meet the requirements.
Assay—
Sodium 1-decanesulfonate solution— Dissolve 0.24g of sodium 1-decanesulfonate in 1liter of water.
Mobile phase— Mix 11.04g of monobasic sodium phosphate and 950mLof water in a beaker.Add 1.3mLof Sodium 1-decanesulfonate solution,and adjust with phosphoric acid to a pHof 2.8.Transfer to a 1-Lvolumetric flask,dilute with water to volume,and pass through a membrane filter.
Standard preparation— Transfer about 50mg of USP Levodopa RS,accurately weighed,to a 100-mLvolumetric flask.Add an accurately weighed quantity of USP Carbidopa RS,which is in a ratio with USP Levodopa RSthat corresponds with the ratio of carbidopa to levodopa in the Tablets.Add 10mLof 0.1Nphosphoric acid.Warm gently to dissolve the standards.Dilute with water to volume,and mix.
Assay preparation— Weigh and finely powder not fewer than 20Tablets.Transfer an accurately weighed portion of the powder,equivalent to about 50mg of levodopa,to a 100-mLvolumetric flask,add 10mLof 0.1Nphosphoric acid,dilute with water to volume,and mix.
Chromatographic system (seeChromatography á621ñ)— The liquid chromatograph is equipped with a 280-nm detector and a 3.9-mm ×30-cm column that contains packing L1.The flow rate,about 2mLper minute,is adjusted until the retention times for levodopa and carbidopa are about 4minutes and 11minutes,respectively.Chromatograph five replicate injections of the Standard preparation,and record the peak responses as directed for Procedure:the relative standard deviation is not more than 2.0%;and the resolution factor between levodopa and carbidopa is not less than 6.
Procedure— Separately inject equal volumes (about 20µL)of the Standard preparationand the Assay preparationinto the chromatograph by means of a suitable microsyringe or sampling valve,record the chromatograms,and measure the responses for the major peaks.Calculate the quantity,in mg,of carbidopa (C10H14N2O4)in the portion of Tablets taken by the formula:
(100C)(rU/rS),
in which Cis the concentration,in mg per mL,of USP Carbidopa RSin the Standard preparation;and rUand rSare the responses of the carbidopa peak obtained from the Assay preparationand the Standard preparation,respectively.Calculate the quantity,in mg,of levodopa (C9H11NO4)by the same formula,reading the terms to refer to levodopa instead of carbidopa.
Auxiliary Information— Staff Liaison:Ravi Ravichandran,Ph.D.,Senior Scientist
Expert Committee:(PA3)Pharmaceutical Analysis 3
USP28–NF23Page 347
Pharmacopeial Forum:Volume No.29(3)Page 615
Phone Number:1-301-816-8330