Methocarbamol

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

Methocarbamol contains NLT 98.5% and NMT 101.5% of methocarbamol (C₁₁H₁₅NO₅), calculated on the dried basis.

2 IDENTIFICATION

Change to read:

A. Spectroscopic Identification Tests 〈197〉, Infrared Spectroscopy: 197K (CN 1-May-2020)

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

Procedure

Buffer: 6.8 g/L of monobasic potassium phosphate in water. Adjust with phosphoric acid or sodium hydroxide to a pH of 4.5.

Mobile phase: Methanol and Buffer (30:70)

System suitability solution: 1.0 mg/mL of USP Methocarbamol RS and 0.005 mg/mL of USP Guaifenesin RS in Mobile phase

Standard solution: 0.1 mg/mL of USP Methocarbamol RS in Mobile phase

Sample solution: 0.1 mg/mL of Methocarbamol in Mobile phase

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: UV 274 nm

Column: 4.6-mm × 15-cm; 3-μm packing L1

Column temperature: 30°

Flow rate: 0.8 mL/min

Injection volume: 20 μL

Run time: 1.5 times the retention time of methocarbamol

System suitability

Samples: System suitability solution and Standard solution

[Note—See Table 1 for relative retention times.]

Suitability requirements

Resolution: NLT 3.5 between methocarbamol and guaifenesin, System suitability solution

Tailing factor: NMT 2.0, Standard solution

Relative standard deviation: NMT 0.73%, Standard solution

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of methocarbamol (C₁₁H₁₅NO₅) in the portion of Methocarbamol taken:

Result = (r_U/r_S) × (C_S/C_U) × 100

r_U = peak response of methocarbamol from the Sample solution

r_S = peak response of methocarbamol from the Standard solution

C_S = concentration of USP Methocarbamol RS in the Standard solution (mg/mL)

C_U = concentration of Methocarbamol in the Sample solution (mg/mL)

Acceptance criteria: 98.5%–101.5% on the dried basis

4 IMPURITIES

Residue on Ignition 〈281〉: NMT 0.1%

Organic Impurities

Mobile phase, System suitability solution, and Chromatographic system: Proceed as directed in the Assay.

Standard solution: 0.005 mg/mL of USP Methocarbamol RS in Mobile phase

Sample solution: 1 mg/mL of Methocarbamol in Mobile phase

System suitability

Samples: System suitability solution and Standard solution

[Note—See Table 1 for the relative retention times.]

Suitability requirements

Resolution: NLT 3.5 between methocarbamol and guaifenesin, System suitability solution

Tailing factor: NMT 2.0, Standard solution

Relative standard deviation: NMT 5.0%, Standard solution

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of each impurity in the portion of Methocarbamol taken:

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

r_U = peak response of each impurity from the Sample solution

r_S = peak response of methocarbamol from the Standard solution

C_S = concentration of USP Methocarbamol RS in the Standard solution (mg/mL)

C_U = concentration of Methocarbamol in the Sample solution (mg/mL)

F = relative response factor (see Table 1)

Acceptance criteria: See Table 1.

Table 1

^a 1-Hydroxy-3-(2-methoxyphenoxy)propan-2-yl carbamate.

^b 4-[(2-Methoxyphenoxy)methyl]-1,3-dioxolan-2-one.

5 SPECIFIC TESTS

Loss on Drying 〈731〉

Analysis: Dry at 60° for 2 h.

Acceptance criteria: NMT 0.5%

6 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in tight containers. Store at controlled room temperature.

USP Reference Standards 〈11〉

USP Guaifenesin RS

USP Methocarbamol RS