(spir on'' oh lak' tone).
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C24H32O4S 416.57
Pregn-4-ene-21-carboxylic acid, 7-(acetylthio)-17-hydroxy-3-oxo-, -lactone, (7,17)-;    
17-Hydroxy-7-mercapto-3-oxo-17-pregn-4-ene-21-carboxylic acid -lactone acetate     [52-01-7].
Spironolactone contains NLT 97.0% and NMT 103.0% of C24H32O4S, calculated on the dried basis.
Change to read:
•  A. Infrared Absorption 197KUSP35
•  B. Ultraviolet Absorption 197U
Sample solution:  10 µg/mL in methanol
Analytical wavelength:  238 nm
Acceptance criteria:  Absorptivities, calculated on the dried basis, do not differ by more than 3.0%.
•  C.
Sample solution:  Add 100 mg to a mixture of 10 mL of water and 2 mL of 1 N sodium hydroxide.
Analysis:  Boil the mixture for 3 min, cool, and add 1 mL of glacial acetic acid and 1 mL of lead acetate TS.
Acceptance criteria:  A brown-to-black precipitate of lead sulfide is formed.
•  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 
Mode:  LC
Detector:  UV 230 nm
Column:  4.6-mm × 15-cm; packing L1
Flow rate:  1 mL/min
Injection size:  20 µL
System suitability 
Sample:  Standard solution
Suitability requirements 
Tailing factor:  NMT 2.0
Relative standard deviation:  NMT 1.5%
Samples:  Standard solution and Sample solution
Calculate the percentage of spironolactone (C24H32O4S) in the portion of sample taken:
Result = (rU/rS) × (CS/CU) × 100
rU== peak response from the Sample solution
rS== peak response from the Standard solution
CS== concentration of USP Spironolactone RS in the Standard solution (mg/mL)
CU== concentration of Spironolactone in the Sample solution (mg/mL)
Acceptance criteria:  97.0%–103.0% on the dried basis
•  Limit of Mercapto Compounds
Sample solution:  Shake 2.0 g with 30 mL of water, and filter.
Analysis:  To 15 mL of the filtrate 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.
•  Ordinary Impurities 466
Standard solution:  Chloroform
Test solution:  Chloroform
Eluant:  Butyl acetate
Visualization:  5
Change to read:
•  Optical Rotation, Specific Rotation 781S: 41 to 45USP35
Sample solution:  10 mg/mL in alcoholUSP35
•  Loss on Drying 731: Dry a sample at 105 for 2 h: it loses NMT 0.5% of its weight.
•  Packaging and Storage: Preserve in well-closed containers.
•  USP Reference Standards 11
USP Spironolactone RS Click to View Structure
Auxiliary Information— Please check for your question in the FAQs before contacting USP.
Topic/Question Contact Expert Committee
Monograph Sujatha Ramakrishna, Ph.D.
Senior Scientific Liaison
(SM22010) Monographs - Small Molecules 2
Reference Standards RS Technical Services
USP35–NF30 Page 4680
Pharmacopeial Forum: Volume No. 37(1)