Misoprostol
(mye'' soe prost' ol).
Click to View Image

C22H38O5 382.53
Prost-13-en-1-oic acid, 11,16-dihydroxy-16-methyl-9-oxo-, methyl ester, (1R*,2R*,3R*,E)-;    
(±)-Methyl (1R,2R,3R)-3-hydroxy-2-[(E)-(4RS)-4-hydroxy-4-methyl-1-octenyl]-5-oxocyclopentaneheptanoate     [59122-46-2].
DEFINITION
Misoprostol contains NLT 97.0% and NMT 102.0% of C22H38O5, calculated on the anhydrous basis.
IDENTIFICATION
•  A. Infrared Absorption 197S
Sample solution:  30 mg/mL
Medium:  Chloroform
•  B. The retention time of the major peak of the Sample solution corresponds to that of the Standard solution, as obtained in the Assay.
ASSAY
•  Procedure
Mobile phase:  2,2,4-Trimethylpentane, dioxane, and acetonitrile (78:21.5:0.5)
Standard solution:  5.0 mg/mL of USP Misoprostol RS in Mobile phase
Sample solution:  5.0 mg/mL of Misoprostol in Mobile phase
Chromatographic system 
Mode:  LC
Detector:  UV 210 nm
Column:  4.6-mm × 25-cm; 5-µm packing L3
Flow rate:  2 mL/min
Injection size:  20 µL
System suitability 
Sample:  Standard solution
[Note—Identify the impurities based on the retention times shown in Impurity Table 1. ]
Suitability requirements 
Resolution:  NLT 1.2, between the second diastereomer peak for 12-epimisoprostol and the Misoprostol peak
Relative standard deviation:  NMT 1.0%, for three replicate injections
Analysis 
Samples:  Standard solution and Sample solution
Calculate the percentage of C22H38O5 in the portion of Misoprostol taken:
Result = (rU/rS) × (CS/CU) × 100
rU== peak response of the Sample solution
rS== peak response of the Standard solution
CS== concentration of the Standard solution (mg/mL)
CU== concentration of the Sample solution (mg/mL)
Acceptance criteria:  97.0%–102.0% on the anhydrous basis
IMPURITIES
Organic Impurities 
•  Procedure 1
Mobile phase, Standard solution, Sample solution, Chromatographic system, and System suitability:  Proceed as directed in the Assay.
Analysis 
Samples:  Standard solution and Sample solution
Record the chromatogram for at least 3 times the retention time of the Misoprostol peak, and measure the peak responses. Identify the impurities based on the retention times shown in Impurity Table 1.
Calculate the percentage of each impurity in the portion of Misoprostol taken:
Result = (rU/rS) × (CS/CU) × (1/F) × 100
rU== peak response of each impurity from the Sample solution
rS== peak response of the Standard solution
CS== concentration of USP Misoprostol RS in the Standard solution (mg/mL)
CU== concentration of Misoprostol in the Sample solution (mg/mL)
F== relative response factor (see Impurity Table 1)
Acceptance criteria 
Individual impurities:  See Impurity Table 1.
Total impurities:  NMT 1.5%
Impurity Table 1
Name Relative
Retention
Time
Relative
Response
Factor
Acceptance
Criteria,
NMT (%)
A-Type misoprostola 0.22 7.8 0.1
B-Type misoprostolb 0.33 0.80 0.1
Norprostolc 0.51 8.4 0.1
8-Epimisoprostold 0.71 1.05 0.3
12-Epimisoprostole 0.86 and 0.92f 1.08 1.0f
Misoprostol 1.0
Any other individual impurity 1.0 0.1
a  Methyl 7-{(1R*,2S*)-2-[(E)-4-hydroxy-4-methyloct-1-enyl]-5-oxocyclopent-3-enyl}heptanoate.
b  (E)-Methyl 7-[2-(4-hydroxy-4-methyloct-1-enyl)-5-oxocyclopent-1-enyl]heptanoate.
c  Methyl 7-(3-hydroxy-5-oxocyclopent-1-enyl)heptanoate.
d  Methyl (1S*,2R*,3R*)-3-hydroxy-2-[(E)-4-hydroxy-4-methyl-1-octenyl]-5-oxocyclopentaneheptanoate.
e  Methyl (1S*,2R*,3S*)-3-hydroxy-2-[(E)-4-hydroxy-4-methyl-1-octenyl]-5-oxocyclopentaneheptanoate.
f  12-Epimisoprostol consists of two diastereomers that are separated under these conditions; integrate both peaks together for the impurity calculations.
•  Procedure 2: Content of Diastereomers
Mobile phase:  Hexane, ethanol, and isopropyl alcohol (94:4:2)
Sample solution:  1.0 mg/mL of Misoprostol in Mobile phase
Chromatographic system 
Mode:  LC
Detector:  UV 205 nm
Column:  4.6-mm × 25-cm; 5-µm packing L3
Column temperature:  40
Flow rate:  1 mL/min
Injection size:  20 µL
System suitability 
Sample:  Sample solution
[Note—Identify the components based on their relative retention times which are about 0.92 for the first diastereomer peak and 1.0 for the second diastereomer peak. ]
Suitability requirements 
Resolution:  NLT 2.0, between the two diastereomer peaks
Relative standard deviation:  NMT 2.0% from the area of the first diastereomer peak
Analysis 
Sample:  Sample solution
Calculate the fraction of the first diastereomer in the portion of Misoprostol taken:
Result = r1/(r1+ r2)
r1== peak response for the first diastereomer
r2== peak response for the second diastereomer
Acceptance criteria 
Fraction of the first diastereomer:  0.51–0.56
SPECIFIC TESTS
ADDITIONAL REQUIREMENTS
•  Packaging and Storage: Preserve in tight containers, and store in a freezer.
•  USP Reference Standards 11
USP Misoprostol RS Click to View Structure
Auxiliary Information— Please check for your question in the FAQs before contacting USP.
Topic/Question Contact Expert Committee
Monograph Elena Gonikberg, Ph.D.
Principal Scientific Liaison
1-301-816-8251
(SM32010) Monographs - Small Molecules 3
Reference Standards RS Technical Services
1-301-816-8129
rstech@usp.org
USP35–NF30 Page 3935
Pharmacopeial Forum: Volume No. 35(3) Page 564