Etomidate Injection
DEFINITION
Etomidate Injection is a sterile, nonpyrogenic solution. It contains NLT 90.0% and NMT 110.0% of the labeled amount of etomidate (C14H16N2O2). It may contain suitable buffers and preservatives.
IDENTIFICATION
•  A. Ultraviolet Absorption 197U
Sample solution:  10 µg/mL of etomidate in isopropyl alcohol
Medium:  Isopropyl alcohol
•  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
Buffer:  0.7 g/L of monobasic sodium phosphate in water
Mobile phase:  Acetonitrile and Buffer (2:3)
Standard solution:  0.16 mg/mL of USP Etomidate RS in acetonitrile
Sample solution:  0.16 mg/mL of etomidate, from the Injection, in acetonitrile
Chromatographic system 
Mode:  LC
Detector:  UV 254 nm
Column:  3.9-mm × 30-cm; packing L1
Flow rate:  2.3 mL/min
Injection size:  20 µL
System suitability 
Sample:  Standard solution
Suitability requirements 
Tailing factor:  NMT 2.0
Relative standard deviation:  NMT 2.0%
Analysis 
Samples:  Standard solution and Sample solution
Calculate the percentage of C14H16N2O2 in the portion of Injection 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 Etomidate RS in the Standard solution (mg/mL)
CU== nominal concentration of etomidate in the Sample solution (mg/mL)
Acceptance criteria:  90.0%–110.0%
IMPURITIES
Organic Impurities 
•  Procedure 1: Related Compounds
Solution A:  Dissolve 6 g of sodium citrate dihydrate and 4 g of anhydrous citric acid in 1 L of water.
Solution B:  Acetonitrile
Mobile phase:  See the gradient table below.
Time
(min)
Solution A
(%)
Solution B
(%)
0 95 5
20 30 70
21 95 5
30 95 5
Diluent:  Weigh 6 g of sodium citrate dihydrate and 4 g of anhydrous citric acid into a 1000-mL volumetric flask. Add 500 mL of water, and shake to dissolve. Add 110 mL of acetonitrile and 50 mL of methanol, and dilute with water to volume.
Standard stock solution:  0.1 mg/mL of USP Metomidate Hydrochloride RS in methanol
Standard solution:  4 µg/mL of USP Metomidate Hydrochloride RS in Diluent, from the Standard stock solution
Sensitivity solution:  0.8 µg/mL of USP Metomidate Hydrochloride RS in Diluent, from the Standard solution
System suitability solution:  0.02 mg/mL of USP Etomidate RS and 0.02 mg/mL of USP Metomidate Hydrochloride RS in Diluent
Sample solution:  0.8 mg/mL of etomidate, from the Injection, in Diluent
Chromatographic system 
Mode:  LC
Detector:  UV 254 nm
Column:  3.9-mm × 30-cm; packing L1
Flow rate:  2.0 mL/min
Injection size:  50 µL
System suitability 
Samples:  Standard solution, Sensitivity solution, and System suitability solution
Suitability requirements 
Resolution:  NLT 2.0 between etomidate and metomidate, System suitability solution
Signal-to-noise ratio:  NLT 10, Sensitivity solution
Relative standard deviation:  NMT 3.0%, Standard solution
Analysis 
Samples:  Standard solution and Sample solution
Calculate the percentage of each impurity in the portion of Injection taken:
Result = (rU/rS) × (CS/CU) × (Mr1/Mr2) × 100
rU== peak response of each individual impurity from the Sample solution
rS== peak response of metomidate from the Standard solution
CS== concentration of USP Metomidate Hydrochloride RS in the Standard solution (mg/mL)
CU== nominal concentration of etomidate in the Sample solution (mg/mL)
Mr1== molecular weight of metomidate free base, 230.26
Mr2== molecular weight of metomidate hydrochloride, 266.72
Acceptance criteria 
Individual impurities:  See Impurity Table 1. [Note—Disregard any impurity peaks less than 0.05%. ]
Total impurities:  NMT 1.6%
Impurity Table 1
Name Relative
Retention
Time
Acceptance
Criteria,
NMT (%)
Etomidate acida 0.34 1.4
Propylene glycol esterb 0.77
Metomidatec 0.90 0.1
Etomidate 1.0
Any unspecified impurity 0.1
a  1-(1-Phenylethyl)-1H-imidazole-5-carboxylic acid.
b  This is quantitated in Procedure 2: Total Propylene Glycol Ester.
c  Methyl 1-(1-phenylethyl)-1H-imidazole-5-carboxylate.
•  Procedure 2: Total Propylene Glycol Ester: [Note—Perform this test if propylene glycol is used in the formulation. ]
Mobile phase and Chromatographic system:  Proceed as directed in the Assay.
Standard solution:  25 µg/mL of USP Etomidate RS in acetonitrile
Sensitivity solution:  1.6 µg/mL of USP Etomidate RS in acetonitrile
Sample solution:  1.6 mg/mL of etomidate, from the Injection, in acetonitrile
System suitability 
Samples:  Standard solution and Sensitivity solution
Suitability requirements 
Tailing factor:  NMT 2.0, Standard solution
Signal-to-noise ratio:  NLT 10, Sensitivity solution
Relative standard deviation:  NMT 3.0%, Standard solution
Analysis 
Samples:  Standard solution and Sample solution
Calculate the percentage of each impurity in the portion of Injection taken:
Result = (rU/rS) × (CS/CU) × (1/F) × 100
rU== peak response of each individual impurity from the Sample solution
rS== peak response of etomidate from the Standard solution
CS== concentration of USP Etomidate RS in the Standard solution (mg/mL)
CU== nominal concentration of etomidate in the Sample solution (mg/mL)
F== relative response factor for each individual impurity (see Impurity Table 2)
Acceptance criteria 
Individual impurities:  See Impurity Table 2. [Note—Disregard any impurity peaks less than 0.05%. ]
Total impurities:  NMT 4.0%. [Note—Total impurities include all impurities from Impurity Table 1 and Impurity Table 2. ]
Impurity Table 2
Name Relative
Retention
Time
Relative
Response
Factor
Acceptance
Criteria,
NMT (%)
Total propylene glycol estera 0.40 0.9 2.8
Etomidate 1.0 1.0
Any unspecified impurity 1.0 0.1
a  2-Hydroxypropyl ester and 2-hydroxy-1-methylethyl ester.
SPECIFIC TESTS
•  Bacterial Endotoxins Test 85: It contains NMT 8.35 USP Endotoxin Units/mg of etomidate.
•  Sterility Tests 71: It meets the requirements when tested as directed for Test for Sterility of the Product to Be Examined, Membrane Filtration.
•  pH 791: Between 4.0 and 7.0
•  Particulate Matter in Injections 788: It meets the requirements for small-volume injections.
•  Other Requirements: It meets the requirements under Injections 1.
ADDITIONAL REQUIREMENTS
•  Packaging and Storage: Preserve in single-dose containers. Store at controlled room temperature.
•  USP Reference Standards 11
USP Endotoxin RS
USP Etomidate RS Click to View Structure
USP Metomidate Hydrochloride RS
Methyl 1-(1-phenylethyl)-1H-imidazole-5-carboxylate hydrochloride.
    C13H14N2O2· HCl        266.72
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USP35–NF30 Page 3144
Pharmacopeial Forum: Volume No. 36(4) Page 919