Iohexol Injection
Iohexol Injection is a sterile solution of Iohexol in Water for Injection. It contains NLT 95.0% and NMT 105.0% of the labeled amount of Iohexol (C19H26I3N3O9) as organically bound iodine. It may contain small amounts of suitable buffers and Edetate Calcium Disodium as a stabilizer. Iohexol Injection intended for intravascular or intrathecal use contains no antimicrobial agents.
•  The retention times of the major peaks in the Sample solution match those of the major peaks in the System suitability solution in the test for Organic Impurities.
•  Procedure
Analysis:  Transfer a volume of Injection, equivalent to 300 mg of iodine, to a glass-stoppered, 250-mL conical flask. Add 25 mL of 1.25 N sodium hydroxide and 500 mg of powdered zinc, connect the flask to a reflux condenser, and reflux the solution for 1 h. Cool the flask to room temperature, rinse the condenser with 20 mL of water, disconnect the flask from the condenser, and filter the mixture. Rinse the flask and the filter thoroughly with small portions of water, adding the rinsings to the filtrate. Add 5 mL of glacial acetic acid, and titrate with 0.1 N silver nitrate VS. Each mL of 0.1 N silver nitrate is equivalent to 27.37 mg of C19H26I3N3O9.
Acceptance criteria:  95.0%–105.0%
Organic Impurities 
•  Procedure
Solution A:  Acetonitrile
Solution B:  Water
Mobile phase:  The percentage of Solution A increases from 1% to 13% at a rate of 0.2%/min.
System suitability solution:  1.5 mg/mL, 0.0075 mg/mL, and 0.0069 mg/mL each of USP Iohexol RS, USP Iohexol Related Compound A RS, and USP Iohexol Related Compound C RS in water
Sample solution:  1.5 mg/mL of Iohexol
Chromatographic system 
Mode:  LC
Detector:  UV 254 nm
Column:  4.6-mm × 25-cm stainless steel column; packing L1
Flow rate:  1.0 mL/min
Injection size:  10 µL
System suitability 
Sample:  System suitability solution
[Note—The relative retention times for the exo-isomer of iohexol and the O-alkylated compounds are 1.0 and between 1.1 and 1.4, respectively. ]
[Note—The peak area of iohexol related compound C is 0.5% ± 0.1% compared to the total area of all the peaks in the chromatogram. ]
Suitability requirements 
Resolution:  NLT 20.0 between iohexol related compound A and iohexol related compound C
Sample:  Sample solution
Excluding peaks with retention times between 0.84 (relative to the endo-isomer of iohexol which is the first main peak) and 1.0, calculate the percentage of O-alkylated compounds, and any other individual impurity peak, in the portion of Iohexol taken:
Result = (rU/rT) × 100
rU== peak response of each impurity
rT== sum of all the peak responses
Acceptance criteria 
Individual impurity:  NMT 0.6% of O-alkylated compounds; NMT 0.1% of any other individual impurity
Total impurities:  NMT 0.3 %, excluding O-alkylated compounds
•  Bacterial Endotoxins Test 85: NMT 0.2 USP Endotoxin Unit per 50 mg of iodine
•  pH 791: 6.8–7.7
•  Particulate Matter in Injections 788: The Injection labeled for intrathecal use meets the requirements for small-volume injections.
•  Free Iodide: Transfer 5.0 mL of Injection to a suitable container, add 20 mL of water, and titrate with 0.001 N silver nitrate VS using a silver electrode in combination with an appropriate reference electrode. Each mL of 0.001 N silver nitrate is equivalent to 0.1269 mg of iodine.
Acceptance criteria:  NMT 0.02%, based on the content of iohexol
•  Injections 1: Meets the requirements
•  Packaging and Storage: Preserve Injection intended for intravascular or intrathecal use in single-dose containers of Type I glass or plastic bottles, protected from light. Store at controlled room temperature.
•  Labeling: Label containers of Injection to direct the user to discard any unused portion. The labeling states also that it is not to be used if it is discolored or contains a precipitate. Label it also to state its routes of administration.
•  USP Reference Standards 11
USP Endotoxin RS
USP Iohexol RS Click to View Structure
USP Iohexol Related Compound A RS
USP Iohexol Related Compound C RS
Auxiliary Information— Please check for your question in the FAQs before contacting USP.
Topic/Question Contact Expert Committee
Monograph Ravi Ravichandran, Ph.D.
Principal Scientific Liaison
(SM42010) Monographs - Small Molecules 4
85 Radhakrishna S Tirumalai, Ph.D.
Principal Scientific Liaison
(GCM2010) General Chapters - Microbiology
Reference Standards RS Technical Services
USP35–NF30 Page 3536
Pharmacopeial Forum: Volume No. 36(1) Page 106