Iohexol is a non-ionic, water-soluble iodinated radiocontrast agent used in medical imaging. It is sold under the trade names Omnipaque, Iodaque, Hexopaque, Oraltag, and others, and is listed on the World Health Organization's Model List of Essential Medicines.
Chemical Properties
- Chemical formula: C₁₉H₂₆I₃N₃O₉
- Molar mass: 821.142 g/mol
- IUPAC name: 1-N,3-N-Bis(2,3-dihydroxypropyl)-5-[N-(2,3-dihydroxypropyl)acetamido]-2,4,6-triiodobenzene-1,3-dicarboxamide
- CAS number: 66108-95-0
- Melting point: 174–180 °C (345–356 °F)
- Osmolality: Ranges from 322 mOsm/kg to 844 mOsm/kg, making it a low-osmolality contrast agent relative to older agents such as diatrizoate.
Medical Uses
Iohexol is used to enhance the visibility of internal structures during X-ray imaging and computed tomography (CT). Specific applications include:
- Angiography (visualization of arteries and veins)
- Myelography (imaging of the spinal canal and nerve roots)
- Arthrography (imaging of joints)
- CT scans of the abdomen, pelvis, brain, and other regions
- Ventriculography (imaging of brain ventricles)
- Urography (imaging of the urinary system)
It can be administered by several routes: intravenous injection, intrathecal injection (into the spinal canal), oral ingestion, rectal administration, intraarticular injection (into joints), or intracavitary instillation.
Mechanism of Action
The three iodine atoms in each iohexol molecule attenuate X-rays in direct proportion to the concentration of the agent. As the concentration changes over time following administration, iohexol provides time-dependent image contrast that helps distinguish anatomical structures.
Pharmacokinetics
- Protein binding: Low
- Metabolism: Nil (excreted unchanged)
- Elimination half-life: Variable
- Excretion: Renal (via the kidneys, unchanged)
Adverse Effects
Common side effects following intravenous injection include:
- Pain at the injection site (≈3%)
- Blurring of vision (≈2%)
- Nausea (≈2%)
- Arrhythmia (≈2%)
- Taste perversion (≈1%)
- Hypotension (≈0.7%)
- Vomiting (≈0.7%)
Less common but more serious effects include allergic reactions, seizures, and kidney problems. Use in late pregnancy may cause hypothyroidism in the newborn. Contrary to common belief, allergies to povidone-iodine or shellfish do not increase the risk of adverse reactions more than other allergies.
Available Forms
Iohexol is available in various concentrations ranging from 140 to 350 milligrams of iodine per milliliter. It is also used as a density gradient medium in laboratory settings under the names Accudenz, Histodenz, and Nycodenz.
History and Regulatory Status
Iohexol was approved for medical use in 1985. It is a prescription-only medication in Canada, the United States, and most other jurisdictions. It belongs to the ATC code V08AB02 (WHO classification for water-soluble, nephrotropic, low-osmolar X-ray contrast media).
