Carbidopa and Levodopa Tablets

This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition

Issued and maintained by the United States Pharmacopeial Convention (USP)

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1 DEFINITION

Carbidopa and Levodopa Tablets contain NLT 90.0% and NMT 110.0% of the labeled amount of carbidopa (C₁₀H₁₄N₂O₄) and levodopa (C₉H₁₁NO₄).

2 IDENTIFICATION

A. The UV spectra of the carbidopa and levodopa peaks of Sample solution A and Sample solution B, respectively, correspond to those of the Standard solution, as obtained in the Assay.

B. The retention times of the carbidopa and levodopa peaks of Sample solution A and Sample solution B, respectively, correspond to those of the Standard solution, as obtained in the Assay.

3 ASSAY

PROCEDURE

Protect solutions containing carbidopa or levodopa from light and maintain them at 2"-8" until they are injected. Use within 12 h.

Buffer: 6 g/L of anhydrous monobasic sodium phosphate in water, adjusted with phosphoric acid to a pH of 2.2

Mobile phase: Alcohol and Buffer (5:95)

Standard solution: 125 µg/mL of USP Carbidopa RS and 125 µg/mL of USP Levodopa RS in Mobile phase

System suitability solution: 2.5 µg/mL of USP Levodopa Related Compound B RS in Standard solution

Sample solution A: Nominally 125 µg/mL of carbidopa from Tablets prepared as follows. Transfer a suitable portion of powder from Tablets (NLT 10) to an appropriate volumetric flask. Add 80% of the total flask volume of Mobile phase. Sonicate for 15 min with intermittent shaking. Dilute with Mobile phase. Centrifuge the resulting solution and use the supernatant.

[NOTE-The use of a centrifuge speed of 3000 rpm for 5 min may be suitable.]

Sample solution B: Nominally 125 µg/mL of levodopa from Sample solution A in Mobile phase

Chromatographic system

(See Chromatography (621), System Suitability.)

Mode: LC

Detector: UV 280 nm. For Identification A, use a diode array detector in the range of 210-400 nm.

Column: 4.6-mm x 15-cm; 5-µm packing L1

Autosampler temperature: 5°

Flow rate: 1 mL/min

Injection volume: 20 µL

Run time: NLT 5 times the retention time of carbidopa

System suitability

Samples: Standard solution and System suitability solution

[NOTE-See Table 1 for the relative retention times.]

Suitability requirements

Resolution: NLT 1.5 between levodopa related compound B and carbidopa, System suitability solution

Tailing factor: NMT 2.0 each for levodopa and carbidopa, Standard solution

Relative standard deviation: NMT 1.0% each for levodopa and carbidopa, Standard solution

Analysis

Samples: Standard solution, Sample solution A, and Sample solution B

Calculate the percentage of the labeled amount of carbidopa (C₁₀H₁₄N₂O₄) in the portion of Tablets taken:

Result = (r_U/r_S) x (C_S/C_U) × 100

r_U = peak response of carbidopa from Sample solution A

r_S = peak response of carbidopa from the Standard solution

C_U = concentration of USP Carbidooa RS in the Standard solution (µg/mL)

C_S = nominal concentration of carbidopa in Sample solution A (ug/ml)

Calculate the percentage of the labeled amount of levodopa (C₉H₁₁NO₄) in the portion of Tablets taken:

Result = (r_U/r_S) x (C_S/C_U) ×100

r_U = peak response of levodopa from Sample solution B

r_S = peak response of levodopa from the Standard solution

C_U = concentration of USP Levodopa RS in the Standard solution (µg/mL)

C_S = nominal concentration of levodopa in Sample solution B (µg/mL)

Acceptance criteria: 90.0%-110.0% of the labeled amount of carbidopa; 90.0%-110.0% of the labeled amount of levodopa

4 PERFORMANCE TESTS

Change to read:

DISSOLUTION (711)

Test 1

Medium: 0.1 N hydrochloric acid: 750 mL

Apparatus 1: 50 rpm

Time: 30 min

Diluent: 0.24 g/L of sodium 1-decanesulfonate in water

Mobile phase: 11.0 g/L of monobasic sodium phosphate in solution, prepared as follows. Transfer a sufficient quantity of monobasic sodium phosphate into a container, and dissolve in water, using 95% of the total volume. Add 0.13% of the total volume of Diluent, and adjust with phosphoric acid to a pH of 2.8. Transfer to a suitable volumetric flask, and dilute with water to volume.

Standard solution: (1,/750) mg/mL of USP Levodopa RS and (L/750) mg/ml, of USP Carbidopa RS in Medium, where L, and L, are the label claims of levodopa and carbidopa, respectively, in mg/Tablet

Sample solution: A filtered portion of the solution under test

Chromatographic system

(See Chromatography (621), System Suitability.)

Mode: LC

Detector: UV 280 nm

Column: 3.9-mm x 30-cm; 10-µm packing 11

Flow rate: 2 mL/min

Injection volume: 20 μL

Run time: NLT 2 times the retention time for carbidopa

System suitability

Sample: Standard solution

[NOTE-The relative retention times for levodopa and carbidopa are 0.4 and 1.0, respectively.]

Suitability requirements

Resolution: NLT 6 between levodopa and carbidopa

Relative standard deviation: NMT 2.0% for levodopa; NMT 2.0% for carbidopa

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of the labeled amount of carbidopa (C₁₀H₁₄N₂O₄) and levodopa (C₉H₁₁NO₄) dissolved:

Result = (r_U/r_S)xC_SxVx (1/L) ×100

r_U = peak response of carbidopa or levodopa from the Sample solution

r_S = peak response of carbidopa or levodopa from the Standard solution

C_S = concentration of USP Carbidopa RS or USP Levodopa RS in the Standard solution (mg/mL)

V = volume of the Medium, 750 mL

L = label claim of carbidopa or levodopa (mg/Tablet)

Tolerances: NLT 80% (Q) of the labeled amount of carbidopa (C₁₀H₁₄N₂O₄) and levodopa (C₉H₁₁NO₄) are dissolved.

Test 2: If the product complies with this test, the labeling indicates that it meets USP Dissolution Test 2.

Medium: 0.1 N hydrochloric acid: 750 mL

Apparatus 1: 100 rpm

Time: 15 min

Solution A: 0.24 g/L of sodium 1-decanesulfonate in water

Mobile phase: 11.0 g/L of monobasic sodium phosphate in solution, prepared as follows. Transfer a sufficient quantity of monobasic sodium phosphate into a container, and dissolve in water, using 95% of the final volume. Add 0.13% of the final volume of Solution A, and adjust with phosphoric acid to a pH of 2.8. Transfer to a suitable volumetric flask, and dilute with water to volume.

Standard solution: (L/750) mg/mL of USP Levodoga RS and (L/750) mg/mL of USP Carbidopa RS in Medium, where L, and L, are the label claims of levodopa and carbidopa, respectively, in mg/Tablet

Sample solution: Pass a portion of the solution under test through a suitable filter.

Chromatographic system

(See Chromatography (621), System Sultability.)

Mode: LC

Detector: UV 280 nm

Column: 3.9-mm x 30-cm; 10-µm packing L1

Flow rate: 2 mL/min

Injection volume: 40 µL

Run time: NLT 2 times the retention time for carbidopa

System suitability

Sample: Standard solution

[NOTE-The relative retention times for levodopa and carbidopa are 0.4 and 1.0, respectively.]

Suitability requirements

Resolution: NLT 6 between levodopa and carbidopa

Relative standard deviation: NMT 2.0% for levodopa; NMT 2.0% for carbidopa

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of the labeled amount of carbidopa (C₁₀H₁₄N₂O₄) and levodopa (C₉H₁₁NO₄) dissolved:

Result = (r_U/r_S)xC_sxVx (1/L) ×100

r_U = peak response of carbidopa or levodopa from the Sample solution

r_S = peak response of carbidopa or levodopa from the Standard solution

C_S = concentration of USP Carbidopa RS or USP Levodopa RS in the Standard solution (mg/mL)

V = volume of the Medium, 750 mL

L = label claim of carbidopa or levodopa (mg/Tablet)

Tolerances: NLT 80% (Q) of the labeled amount of carbidopa (C₁₀H₁₄N₂O₄) and levodopa (C₉H₁₁NO₄) are dissolved.

Test 3: If the product complies with this test, the labeling indicates that it meets USP Dissolution Test 3.

Medium: 0.1 N hydrochloric acid: 750 mL, deaerated

Apparatus 1: 65 rpm

Time: 30 min

Solution A: 0.24 g/L of sodium 1-decanesulfonate in water

Mobile phase: 12.5 g/L of monobasic sodium phosphate dihydrate in solution, prepared as follows. Transfer a sufficient quantity of monobasic sodium phosphate dihydrate into a suitable volumetric flask, and dissolve in water, using 95% of the final volume. Add 0.13% of the final volume of Solution A, and adjust with phosphoric acid to a pH of 2.8. Dilute with water to volume.

Carbidopa standard stock solution: 0.19 mg/mL of USP Carbidoga RS in Medium. Sonicate to dissolve if necessary.

Levodopa standard stock solution: 1.1 mg/mL of USP Levodopa RS in Medium. Sonicate to dissolve if necessary.

Standard solution

For Tablets labeled to contain 25-mg carbidopa/100-mg levodopa or 25-mg carbidopa/250-mg levodopa: 0.038 mg/mL of USP

Carbidopa RS from Carbidopa standard stock solution and 0.22 mg/mL of USP Levodopa RS from Levodopa standard stock solution in Medium

For Tablets labeled to contain 10-mg carbidopa/100-mg levodopa: 0.015 mg/mL of USP Carbidopa RS from Carbidopa standard stock solution and 0.132 mg/mL of USP Levodopa RS from Levodopa standard stock solution in Medium

Sample solution: Pass a portion of the solution under test through a suitable filter of 0.45-um pore size, discarding the first 2 mL of filtrate.

Chromatographic system

(See Chromatography (621). System Suitability.)

Mode: LC

Detector: UV 280 nm

Column: 3,9-mm x 30-cm; 10-µm packing Li

Flow rate: 2 mL/min

Injection volume: 20 µL

Run time: NLT 2 times the retention time for carbidopa

System suitability

Sample: Standard solution

[NOTE-The relative retention times for levodopa and carbidopa are 0.4 and 1.0, respectively.]

Suitability requirements

Resolution: NLT 6 between levodopa and carbidopa

Relative standard deviation: NMT 2.0% each for levodopa and carbidopa

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of the labeled amount of carbidopa (C₁₀H₁₄N₂O₄) and levodopa (C₉H₁₁NO₄) dissolved:

Result = (r_U/r_S)xC_SxVx(1/L) ×100

r_U = peak response of carbidopa or levodopa from the Sample solution

r_S = peak response of carbidopa or levodopa from the Standard solution

C_S = concentration of USP Carbidopa RS or USP Levodopa RS in the Standard solution (mg/mL)

V = volume of the Medium, 750 mL

L = label claim of carbidopa or levodopa (mg/Tablet)

Tolerances: NLT 80% (Q) of the labeled amount of carbidopa (C₁₀H₁₄N₂O₄) and levodopa (C₉H₁₁NO₄) are dissolved.

Test 4: If the product complies with this test, the labeling indicates that it meets USP Dissolution Test 4.

Medium: 0.1 N hydrochloric acid: 500 mL

Apparatus 1: 100 rpm

Time: 30 min

Mobile phase: Dissolve 13.6 g of potassium phosphate monobasic in 1000 ml, of water. Adjust with phosphoric acid to a pH of 3.0.

Standard solution: (L,/500) mg/mL of USP Levodopa RS and (L/500) mg/mL of USP Carbidopa RS in Medium, where L, and L., are the label claims of levodopa and carbidopa, respectively, in mg/Tablet. Sonicate to dissolve.

Sample solution: Pass a portion of the solution under test through a suitable filter of 0.45-µm pore size, discarding an appropriate volume of filtrate so that a consistent result can be obtained.

Chromatographic system

(See Chromatography (621), System Suitability.)

Mode: LC

Detector: UV 282 nm

Column: 4.6-mm x 15-cm; 3.5-µm packing LZ

Flow rate: 1.5 mL/min

Injection volume: 20 µL.

Run time: NLT 1.8 times the retention time for carbidopa

System suitability

Sample: Standard solution

[NOTE-The relative retention times for levodopa and carbidopa are 0.4 and 1.0, respectively.]

Suitability requirements

Tailing: NMT 2.0 for levodopa; NMT 2.0 for carbidopa

Relative standard deviation: NMT 2.0% each for levodopa and carbidopa

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of the labeled amount of carbidopa (C₁₀H₁₄N₂O₄) and levodopa (C₉H₁₁NO₄) dissolved:

Result = (r_U/r_S) x C_S x V x (1/L) x 100

r_U = peak response of carbidopa or levodopa from the Sample solution

r_S = peak response of carbidopa or levodopa from the Standard solution

C_S = concentration of USP Carbidopa RS or USP Levodopa RS in the Standard solution (mg/mL)

V = volume of the Mediurn, 500 mL

L = label claim of carbidopa or levodopa (mg/Tablet)

Tolerances: NLT 80% (Q) of the labeled amount of carbidopa (C₁₀H₁₄N₂O₄) and levodopa (C₉H₁₁NO₄) are dissolved. (RB 1-Oct-2023)

UNIFORMITY OF DOSAGE UNITS (905): Meet the requirements

5 IMPURITIES

ORGANIC IMPURITIES

Protect solutions containing carbidopa or levodopa from light and maintain them at 2-8° until they are injected. Use within 12 h.

Mobile phase and Chromatographic system: Proceed as directed in the Assay.

System suitability solution: 125 µg/mL of USP Carbidopa RS, 0.25 µg/mL of dihydroxybenzaldehyde, 1.25 µg/mL of dihydroxyphenylacetone, and 2.5 µg/mL of USP Levodopa Related Compound B RS in Mobile phase

Standard solution: 1.25 µg/mL of USP Carbidopa RS and 5 µg/mL of USP Levodopa RS in Mobile phase

Sample solution: Nominally 125 µg/mL of carbidopa from Tablets prepared as follows. Transfer a suitable amount of powder from Tablets (NLT 10) to an appropriate volumetric flask. Add 80% of the total flask volume of Mobile phase. Sonicate for 15 min with intermittent shaking. Dilute with Mobile phase. Centrifuge the resulting solution and use the supernatant.

[NOTE-The use of a centrifuge speed of 3000 rpm for 5 min may be suitable.]

System suitability

Samples: System suitability solution and Standard solution

[NOTE-See Table 1 for the relative retention times.]

Suitability requirements

Resolution: NLT 1.5 between levodopa related compound B and carbidopa, NLT 1.5 between dihydroxybenzaldehyde and dihydroxyphenylacetone, System suitability solution

Relative standard deviation: NMT 3.0% each for levodopa and carbidopa, Standard solution

Signal-to-noise ratio: NLT 10 for dihydroxybenzaldehyde and dihydroxyphenylacetone, System suitability solution

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of methyldopa and dihydroxyphenylacetone in the portion of Tablets taken:

Result = (r_U/r_S) x (C_S/C_U) × (1/F) ×100

r_U = peak response of methyldopa or dihydroxyphenylacetone from the Sample solution

r_S = peak response of carbidopa from the Standard solution

C_U = concentration of USP Carbidora RS in the Standard solution (µg/mL)

C_S = nominal concentration of carbidopa in the Sample solution (µg/mL)

F = relative response factor (see Table 1)

Calculate the percentage of any unspecified degradation product in the portion of Tablets taken:

Result = (r_U/r_S) x (C_S/C_U) × (1/F) x 100

r_U = peak response of any unspecified degradation product from the Sample solution

r_S = peak response of levodopa from the Standard solution

C_U = concentration of USP Levodopa RS in the Standard solution (µg/mL)

C_S = nominal concentration of levodopa in the Sample solution (µg/mL)

F = relative response factor (see Table 1)

Acceptance criteria: See Table 1. The reporting thresholds are 0.1% and 0.05% for peaks associated with carbidopa and levodopa, respectively.

Table 1

^a Process impurity is included in the table for identification only. Process impurities are controlled in the drug substance and are not to be reported or included in the total impurities for the drug product.

^b 3-(2,4,5-Trihydroxyphenyl)-l-alanine.

^c 3,4-Dihydroxybenzaldehyde.

^d 3,4-Dihydroxyphenylacetone.

^e (S)-2-Hydrazinyl-3-(4-hydroxy-3-methoxyphenyl)-2-methylpropanoic acid; also known as 3-O-methylcarbidopa.

6 ADDITIONAL REQUIREMENTS

Packaging and Storage: Dispense in a tight, light-resistant container. Store at controlled room temperature.

Labeling: The labeling states the Dissolution test used only if Test 1 is not used.

USP Reference Standards 〈11〉

USP Carbidopa RS

USP Levodopa RS

USP Levodopa Related Compound B RS

3-Methoxy-l-tyrosine;

Also known as 3-Methoxytyrosine.

C₁₃H₁₄NO₄ 211.22