Spironolactone

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

Spironolactone contains NLT 97.0% and NMT 103.0% of spironolactone (C₂₄H₃₂O₄S), calculated on the dried basis.

2 IDENTIFICATION

Change to read:

A. SPECTROSCOPIC IDENTIFICATION TESTS 〈197〉 , Infrared Spectroscopy: 197A or 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

Mobile phase: Methanol and water (60:40)

Standard solution: 0.5 mg/mL of USP Spironolactone RS in a mixture of acetonitrile and water (1:1) Sample solution: 0.5 mg/mL of Spironolactone in a mixture of acetonitrile and water (1:1)

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: UV 230 nm

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

Flow rate: 1 mL/min

Injection volume: 20 µL

Run time: NLT 2 times the retention time of spironolactone

System suitability

Sample: Standard solution

Suitability requirements

Tailing factor: NMT 2.0

Relative standard deviation: NMT 1.10%

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of spironolactone (C₂₄H₃₂O₄S) in the portion of Spironolactone taken:

Result = (r_U/r_S) × (C_S/C_U) × 100

r_U = peak response of spironolactone from the Sample solution

r_S = peak response of spironolactone from the Standard solution

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

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

Acceptance criteria: 97.0%–103.0% on the dried basis

4 IMPURITIES

4.1 LIMIT OF MERCAPTO COMPOUNDS

Sample solution: Shake 2.0 g with 30 mL of water, and filter.

Analysis: To 15 mL of the Sample solution add 3 mL of starch TS, and titrate with 0.010 N iodine. Perform a blank determination, and make any necessary correction.

Acceptance criteria: NMT 0.10 mL of 0.010 N iodine is consumed.

4.2 ORGANIC IMPURITIES

Diluent: Acetonitrile and water (50:50)

Mobile phase: Acetonitrile, tetrahy drofuran, methanol, and water (15:20:425:540)

Standard stock solutions: 2 mg/mL of USP Spironolactone RS and 0.2 mg/mL each of USP Spironolactone Related Compound A RS, USP Spironolactone Related Compound B RS, USP Spironolactone Related Compound C RS, USP Spironolactone Related Compound D RS, USP Spironolactone Epimer Mixture RS, and USP Spironolactone Related Compound I RS prepared separately as follows. Dissolve each suitable amount of the corresponding USP Reference Standard in a suitable volumetric flask in about 10% of the total volume of tetrahydrofuran.

Dilute with Diluent to volume.

Standard solution: 0.002 mg/mL of USP Spironolactone RS and 0.006 mg/mL of USP Spironolactone Related Compound A RS in Diluent from the corresponding Standard stock solutions

System suitability solution: 0.02 mg/mL of USP Spironolactone RS and 0.006 mg/mL each of USP Spironolactone Related Compound A RS, USP Spironolactone Related Compound B RS, USP Spironolactone Related Compound C RS, USP Spironolactone Related Compound D RS, USP Spironolactone Epimer Mixture RS, and USP Spironolactone Related Compound I RS in Diluent from the corresponding Standard stock solutions

Sensitivity solution: 0.001 mg/mL of USP Spironolactone RS in Diluent from the corresponding Standard stock solution

Sample solution: 2 mg/mL of Spironolactone prepared as follows. Dissolve a suitable amount of Spironolactone in about 10% of the total volume of tetrahydrofuran and dilute with Diluent to volume.

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: UV 254 nm

Column: 4.6-mm × 15-cm; 3.5-µm packing L1

Column temperature: 40°

Flow rate: 1 mL/min Injection volume: 20 µL

Run time: NLT 2.8 times the retention time of the spironolactone peak

System suitability

Samples: Standard solution, System suitability solution, and Sensitivity solution

Suitability requirements

Resolution: NLT 1.2 between spironolactone and spironolactone related compound B, System suitability solution Relative standard deviation: NMT 5.0% for the spironolactone peak, Standard solution

Signal-to-noise ratio: NLT 20, Sensitivity solution

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of spironolactone related compound A in the portion of Spironolactone taken:

Result = (r_U/r_S) × (C_S/C_U) × 100

r_U = peak response of spironolactone related compound A from the Sample solution

r_S = peak response of spironolactone related compound A from the Standard solution

C_S = concentration of USP Spironolactone Related Compound A RS in the Standard solution (mg/mL)

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

Calculate the percentage of each impurity, other than spironolactone related compound A, in the portion of Spironolactone taken:

Result = (r_U/r_S) × (C_S/C_U) × 100

r_U = peak response of each impurity, other than spironolactone related compound A, from the Sample solution

r_S = peak response of spironolactone from the Standard solution

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

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

Acceptance criteria: See Table 1. The reporting threshold is 0.05%.

Table 1

5 SPECIFIC TESTS

OPTICAL ROTATION 〈781S〉 , Procedures, Specific Rotation Sample solution: 10 mg/mL in alcohol

Acceptance criteria: −41° to −45°

LOSS ON DRYING 〈731〉

Analysis: Dry at 105° for 2 h.

Acceptance criteria: NMT 0.5%

6 ADDITIONAL REQUIREMENTS

PACKAGING AND STORAGE: Preserve in well-closed containers.

USP REFERENCE STANDARDS 〈11〉

USP Spironolactone RS

USP Spironolactone Related Compound A RS

(2′R)-3′,4′-Dihydro-5′H-spiro[androst-4,6-diene-17,2′-furan]-3,5′-dione.    C₂₂H₂₈O₃         340.46

USP Spironolactone Related Compound B RS

(2′R)-7α-(Acetylthio)-5′H-spiro[androst-4-ene-17,2′-furan]-3,5′-dione.  C₂₄H₃₀O₄S    414.56

USP Spironolactone Related Compound C RS

(2′R)-3′,4′-Dihydro-5′H-spiro[androst-4-ene-17,2′-furan]-3,5′-dione.  C₂₂H₃₀O₃     342.47

USP Spironolactone Related Compound D RS

(2′R)-7α-(Acetyldisulfanyl)-3′,4′-dihydro-5′H-spiro[androst-4-ene-17,2′-furan]-3,5′-dione.   C₂₄H₃₂O₄S₂      448.64

USP Spironolactone Epimer Mixture RS

It contains a mixture of approximately 39% of spironolactone and 56% of 7-epispironolactone: (2′R)-7β-(Acetylthio)-3′,4′-dihydro-5′H-spiro[androst-4-ene-17,2′-furan]-3,5′-dione.   C₂₄H₃₂O₄S    416.57

USP Spironolactone Related Compound I RS

S-[17α-(Ethoxymethyl)-17-hydroxy-3-oxoandrost-4-en-7α-yl]ethanethioate. C₂₄H₃₆O₄S    420.61