Chlorzoxazone Tablets
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This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition
Issued and maintained by the United States Pharmacopeial Convention (USP)
1 DEFINITION
Chlorzoxazone Tablets contain NLT 90.0% and NMT 110.0% of the labeled amount of chlorzoxazone (C7H4ClNO2).
2 IDENTIFICATION
A. ULTRAVIOLET ABSORPTION
Standard solution: 0.02 mg/mL of USP Chlorzoxazone RS in methanol
Sample stock solution: Nominally 1.0 mg/mL of chlorzoxazone from Tablets prepared as follows. Disperse a portion of powdered Tablets, equivalent to 100 mg of chlorzoxazone, in 100 mL of methanol and shake for 15 min. Pass the resulting solution through a suitable filter.
Sample solution: Nominally 0.02 mg/mL of chlorzoxazone from Sample stock solution in methanol
Acceptance criteria: The UV absorption spectrum of the Sample solution exhibits maxima and minima at the same wavelengths as those of the Standard solution, concomitantly measured.
B. The retention time of the major peak of the Sample solution corresponds to that of the Standard solution, as obtained in the Assay.
3 ASSAY
3.1 PROCEDURE
Solution A: Dilute 10 mL of glacial acetic acid with water to make 1000 mL of solution. Mobile phase: Acetonitrile, water, and glacial acetic acid (30:70:1)
Internal standard solution: 1.25 mg/mL of phenacetin in acetonitrile
Standard stock solution: 1.25 mg/mL of USP Chlorzoxazone RS in Mobile phase
Standard solution: 0.125 mg/mL of USP Chlorzoxazone RS from Standard stock solution and 0.25 mg/mL of phenacetin from Internal standard solution in Solution A
System suitability stock solution: 8.5 mg/mL of p-chlorophenol in acetonitrile
System suitability solution: 0.17 mg/mL of p-chlorophenol from System suitability stock solution, 0.1 mg/mL of USP Chlorzoxazone RS from Standard stock solution, and 0.25 mg/mL of phenacetin from Internal standard solution in Solution A
Sample stock solution: Nominally 1.25 mg/mL of chlorzoxazone prepared as follows. Finely powder Tablets (NLT 20) and transfer a portion of powder to an appropriate volumetric flask. Add 70% of the flask volume of acetonitrile, and shake by mechanical means for about 30 min. Dilute with acetonitrile to volume. Filter a portion of this solution, discarding the first 10 mL of the filtrate.
Sample solution: Nominally 0.125 mg/mL of chlorzoxazone from Sample stock solution and 0.25 mg/mL of phenacetin from Internal standard solution in Solution A
3.1.1 Chromatographic system
(See Chromatography 〈621〉, System Suitability.) Mode: LC
Detector: UV 280 nm
Column: 4-mm × 30-cm; packing L1 Flow rate: 1.5 mL/min
Injection volume: 20 µL
3.1.2 System suitability
Samples: Standard solution and System suitability solution
[NOTE—The relative retention times for phenacetin, chlorzoxazone, and p-chlorophenol are about 0.7, 1.0, and 1.2, respectively.]
Suitability requirements
Resolution: NLT 2.0 between chlorzoxazone and p-chlorophenol, System suitability solution Relative standard deviation: NMT 2.0%, Standard solution
3.1.3 Analysis
Samples: Standard solution and Sample solution
Calculate the percentage of the labeled amount of chlorzoxazone (C7H4ClNO2) in the portion of Tablets taken:
Result = (Ru/Rs) × (Cs/Cu) × 100
Ru = peak response ratio of chlorzoxazone to phenacetin from the Sample solution
Rs = peak response ratio of chlorzoxazone to phenacetin from the Standard solution
Cs = concentration of USP Chlorzoxazone RS in the Standard solution (mg/mL)
Cu = nominal concentration of chlorzoxazone in the Sample solution (mg/mL)
Acceptance criteria: 90.0%–110.0%
4 PERFORMANCE TESTS
Change to read:
4.1 DISSOLUTION 〈711〉
4.1.1 Test 1
[NOTE—Use 2-L vessels for this test.]
Medium: pH 6.8 phosphate buffer; 1800 mL Apparatus 2: 75 rpm
Time: 60 min
Standard solution: USP Chlorzoxazone RS in Medium
Sample solution: Pass a portion of the solution under test through a suitable filter. Dilute with Medium, if necessary.
4.1.1.1 Instrumental conditions
Mode: UV
Analytical wavelength: 284 nm
4.1.1.2 Analysis
Samples: Standard solution and Sample solution
Determine the percentage of the labeled amount of chlorzoxazone (C7H4ClNO2) dissolved.
Tolerances: NLT 75% (Q ) of the labeled amount of chlorzoxazone (C7H4ClNO2) is dissolved.
4.1.2 Test 2
If the product complies with this test, the labeling indicates that it meets USP Dissolution Test 2. Medium: pH 6.8 phosphate buffer; 1800 mL
Apparatus 2: 75 rpm
Time: 90 min
Standard stock solution: 0.84 mg/mL of USP Chlorzoxazone RS in methanol. Sonicate as necessary to dissolve. Standard solution: 0.021 mg/mL of USP Chlorzoxazone RS from the Standard stock solution in Medium
Sample solution: Pass a portion of the solution under test through a suitable filter. Dilute with Medium.
4.1.2.1 Instrumental conditions
(See Ultraviolet-Visible Spectroscopy 〈857〉.) Mode: UV
Analytical wavelength: 284 nm
4.1.2.2 Analysis
Samples: Standard solution and Sample solution
Calculate the percentage of the labeled amount of chlorzoxazone (C7H4ClNO2) dissolved:
Result = (Au/As) × Cs × V × D × (1/L) × 100
Au = absorbance of chlorzoxazone from the Sample solution
As = absorbance of chlorzoxazone from the Standard solution
Cs = concentration of USP Chlorzoxazone RS in the Standard solution (mg/mL)
V = volume of Medium, 1800 mL
D = dilution factor for the Sample solution
L = label claim (mg/Tablet)
Tolerances: NLT 75% (Q ) of the labeled amount of chlorzoxazone (C7H4ClNO2) is dissolved.
4.1.3 Test 4
If the product complies with this test, the labeling indicates that it meets USP Dissolution Test 4. Medium: 0.2% sodium dodecyl sulfate in water; 1800 mL
Apparatus 2: 100 rpm
Time: 20 min
Mobile phase: Acetonitrile and water (30:70). Add 10 mL of glacial acetic acid to each liter of the mixture.
Standard solution: 0.14 mg/mL of USP Chlorzoxazone RS prepared as follows. Transfer a suitable amount of USP Chlorzoxazone RS to an appropriate volumetric flask. Add 5% of the flask volume of acetonitrile and sonicate to dissolve. Dilute with Medium to volume.
Sample solution: Pass a portion of the solution under test through a suitable filter.
4.1.3.1 Chromatographic system
(See Chromatography 〈621〉, System Suitability.) Mode: LC
Detector: UV 280 nm
Column: 4.6-mm × 15-cm; 3-µm packing L1 Flow rate: 1 mL/min
Injection volume: 15 μL
Run time: NLT 2 times the retention time of chlorzoxazone
4.1.3.2 System suitability
Sample: Standard solution
Suitability requirements
Relative standard deviation: NMT 3.0% Analysis
Samples: Standard solution and Sample solution
Calculate the percentage of the labeled amount of chlorzoxazone (C7H4ClNO2) dissolved:
Result = (ru/rs) × Cs × V × (1/L) × 100
ru = peak response of chlorzoxazone from the Sample solution
rs = peak response of chlorzoxazone from the Standard solution
Cs = concentration of USP Chlorzoxazone RS in the Standard solution (mg/mL)
V = volume of Medium, 1800 mL
L = label claim (mg/Tablet)
Tolerances: NLT 80% (Q ) of the labeled amount of chlorzoxazone (C7H4ClNO2) is dissolved.
4.1.4 Test 5
If the product complies with this test, the labeling indicates that it meets USP Dissolution Test 5.
Medium: Phosphate buffer, pH 8.0 (Dissolve 6.8 g of potassium phosphate, monobasic in 1 L water, add 1.85 g of sodium hy droxide and dissolve. Adjust with 1 N sodium hy droxide or 1 N hy drochloric acid to a pH of 8.0, if necessary.); 1800 mL
Apparatus 2: 75 rpm
Time: 60 min
Standard stock solution: 0.3 mg/mL of USP Chlorzoxazone RS prepared as follows. Transfer an appropriate quantity of USP Chlorzoxazone RS to a suitable volumetric flask, add 15% of the flask volume of methanol, and sonicate to dissolve. Dilute with Medium to volume.
Standard solution: 0.03 mg/mL of USP Chlorzoxazone RS from the Standard stock solution in Medium
Sample solution: Pass a portion of the solution under test through a suitable filter of 0.45-μm pore size, discarding NLT 4 mL of filtrate. Dilute with Medium to a concentration similar to that of the Standard solution, if necessary.
4.1.4.1 Instrumental conditions
(See Ultraviolet-Visible Spectroscopy 〈857〉.) Mode: UV
Analytical wavelength: 282 nm
4.1.4.2 Analysis
Samples: Standard solution and Sample solution
Calculate the percentage of the labeled amount of chlorzoxazone (C7H4ClNO2) dissolved:
Result = (Au/As) × Cs × V × D × (1/L) × 100
Au = absorbance of the Sample solution
As = absorbance of the Standard solution
Cs = concentration of USP Chlorzoxazone RS in the Standard solution (mg/mL)
V = volume of Medium, 1800 mL
D = dilution factor for the Sample solution, if necessary
L = label claim (mg/Tablet)
Tolerances: NLT 75% (Q ) of the labeled amount of chlorzoxazone (C7H4ClNO2) is dissolved. (RB 1-Jul-2023)
4.2 UNIFORMITY OF DOSAGE UNITS 〈905〉
Meet the requirements
5 ADDITIONAL REQUIREMENTS
PACKAGING AND STORAGE: Preserve in tight containers.
LABELING: The labeling states the Dissolution test used only if Test 1 is not used.
USP REFERENCE STANDARDS 〈11〉
USP Chlorzoxazone RS
