Oxybutynin Chloride

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

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

DOWNLOAD PDF HERE

C₂₁H₃₁NO₃ · HCl 393.95

Benzeneacetic acid, α-cyclohexyl-α-hydroxy-, 4-(diethyl amino)-2-butynyl ester hydrochloride, (±)-; 4-(Diethylamino)-2-butynyl (±)-α-phenylcyclohexaneglycolate hydrochloride CAS RN®: 1508-65-2; UNII: L9F3D9RENQ.

1 DEFINITION

Oxybutynin Chloride contains NLT 97.0% and NMT 102.0% of oxybutynin chloride (C₂₁H₃₁NO₃ · HCl), 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: A solution containing 6.67 g/L of monobasic potassium phosphate and 8.55 g/L of dibasic potassium phosphate Mobile phase: Acetonitrile and Buffer (49:51)

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

Sample solution: 0.1 mg/mL of Oxybutynin Chloride in Mobile phase

3.1 Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: UV 210 nm

Column: 4.6-mm × 7.5-cm; 3-µm or 3.5-µm packing L7

Column temperature: 45°

Flow rate: 1 mL/min

Injection volume: 10 µL

3.2 System suitability

Sample: Standard solution

Suitability requirements

Relative standard deviation: NMT 1.0%

3.3 Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of oxybutynin chloride (C₂₁H₃₁NO₃ · HCl) in the portion of Oxybutynin Chloride taken: 

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

r_U = peak response from the Sample solution

r_S = peak response from the Standard solution

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

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

Acceptance criteria: 97.0%–102.0% on the dried basis

4 OTHER COMPONENTS

Chloride Content

Sample: 600 mg of Oxybutynin Chloride, previously dried

Analysis: Dissolve the Sample in 100 mL of water, and add 5 mL of nitric acid. Titrate (see Titrimetry 〈541〉) with 0.1 N silver nitrate VS, using a platinum–silver chloride electrode system. Each mL of 0.1 N silver nitrate is equivalent to 3.545 mg of chloride (Cl). Acceptance criteria: 8%–10%

5 IMPURITIES

Residue on Ignition 〈281〉: NMT 0.1%

Organic Impurities

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

System suitability stock solution: 100 µg/mL each of USP Oxybutynin Related Compound B RS and USP Oxybutynin Related Compound C RS in Mobile phase

Standard stock solution: 1.0 mg/mL of USP Oxybutynin Chloride RS in Mobile phase

System suitability solution: Transfer 10.0 mL of the System suitability stock solution to a 100-mL volumetric flask, add 10.0 mL of Standard stock solution, and dilute with Mobile phase to volume.

Standard solution: 7.5 µg/mL of USP Oxybutynin Chloride RS from Standard stock solution in Mobile phase.

Sample solution: 5.0 mg/mL of Oxybutynin Chloride in Mobile phase

5.1 System suitability

Sample: System suitability solution

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

Suitability requirements

Resolution: NLT 1.1 between oxybutynin related compound B and oxybutynin related compound C

Relative standard deviation: NMT 2.0% for the oxybutynin peak

5.2 Analysis

Samples: Standard solution and Sample solution

Record the chromatograms for a total time of NLT twice the retention time of the oxybutynin peak.

Calculate the percentage of each impurity in the portion of Oxybutynin Chloride 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 oxybutynin from the Standard solution

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

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

F = relative response factor for each impurity (see Table 1)

Acceptance criteria: See Table 1.

Table 1

a Phenylcyclohexylglycolic acid (cyclohexylmandelic acid, or CHMA).

b 4-(Diethylamino)but-2-ynyl 2-hydroxy-2,2-diphenylacetate.

c Methyl ester of phenylcyclohexylglycolic acid (methyl ester of cyclohexylmandelic acid, or CHMME).

d Methylethyl analog of oxybutynin chloride (4-(ethylmethylamino) but-2-ynyl (±)-2-cyclohexyl-2-hydroxy-2-phenylacetate).

e 4-(Diethylamino)but-2-ynyl (±)-2-(cyclohex-3-enyl)-2-cyclohexyl-2-hydroxyacetate.

f 4-(Ethylpropylamino)but-2-ynyl (±)-2-cyclohexyl-2-hydroxy-2-phenylacetate.

6 SPECIFIC TESTS

Loss on Drying 〈731〉

Analysis: Dry a sample at 105° for 2 h.

Acceptance criteria: NMT 3%

7 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in well-closed containers.

USP Reference Standards 〈11〉

USP Oxybutynin Chloride RS

USP Oxybutynin Related Compound B RS

Methyl ester of phenylcyclohexylglycolic acid, or CHMME (cyclohexyl mandelic acid methyl ester).

USP Oxybutynin Related Compound C RS

Methylethyl analog of oxybutynin chloride, or 4-(ethylmethylamino) but-2-ynyl (±) 2-cyclohexyl-2-hydroxy-2-phenylacetate hydrochloride.