Iohexol
Iohexol is a nonionic, water-soluble, iodinated contrast agent used in radiographic imaging to enhance the visibility of internal body structures, such as blood vessels, organs, and the gastrointestinal tract, during procedures like computed tomography (CT) scans, angiography, myelography, and arthrography.[1] Marketed under the brand name Omnipaque and generic versions following FDA approval in November 2025, it is available in sterile solutions at iodine concentrations ranging from 140 to 350 mgI/mL, allowing for administration via intravascular, intrathecal, oral, rectal, or intra-articular routes depending on the diagnostic need.[2] As a low-osmolar agent with an osmolality approximately 1.1 to 3.0 times that of plasma, iohexol minimizes the risk of osmotic-related adverse effects compared to high-osmolar ionic contrasts, making it suitable for use in adults, children, and patients with cardiovascular or renal conditions when appropriately dosed.[1] Its primary indications include contrast enhancement for CT imaging of the head, abdomen, and pelvis; excretory urography; intra-arterial and intravenous angiography; and evaluation of joint spaces or the spinal canal.[3] Contraindications include known hypersensitivity to iohexol, with warnings emphasizing risks of allergic reactions, seizures (particularly with intrathecal use), and renal impairment in susceptible individuals; severe dehydration is a risk factor requiring hydration precautions.[1] Chemically, iohexol is the compound 5-[acetyl(2,3-dihydroxypropyl)amino]-N,N'-bis(2,3-dihydroxypropyl)-2,4,6-triiodobenzene-1,3-dicarboxamide, with the molecular formula C19H26I3N3O9 and a molecular weight of 821.14 Da, containing 46.36% organically bound iodine by weight.[4] Pharmacologically, it attenuates X-rays through iodine's high atomic number, providing radiopacity without dissociation into ions, and is rapidly cleared from the body via glomerular filtration in the kidneys, with a plasma half-life of about 2 hours following intravascular administration.[2] This renal elimination underscores the need for hydration and monitoring in patients with impaired kidney function to prevent contrast-induced nephropathy.[3]Medical uses
Indications
Iohexol is a non-ionic iodinated contrast medium primarily used to enhance visibility of internal structures in X-ray-based diagnostic imaging procedures.[2] It works by providing radiopacity through its iodine content, allowing for clearer delineation of anatomical features during various radiological examinations.[5] For intravascular administration, iohexol is indicated in angiography of arteries and veins, including cerebral arteriography, peripheral arteriography, aortography, selective coronary arteriography, pulmonary angiography in pediatric patients, and intra-arterial digital subtraction angiography, as well as for intravenous contrast enhancement in computed tomography (CT) scans of the head, body, and extremities, excretory urography, peripheral venography, and intravenous digital subtraction angiography.[5] Intrathecal use is approved for myelography and CT myelography (lumbar, thoracic, cervical, total columnar) and CT cisternography to visualize the brain ventricles and spinal subarachnoid spaces.[5] Oral or rectal administration supports gastrointestinal tract opacification for radiographic examination and CT of the abdomen and pelvis.[5] Intra-articular injection is indicated for arthrography to assess joint structures.[5] In body cavity procedures, iohexol is used for hysterosalpingography (in non-pregnant adults), endoscopic retrograde cholangiopancreatography, herniography, and voiding cystourethrography to evaluate the urinary tract and other cavities.[5] These applications enable detailed visualization of blood vessels, the urinary tract, brain ventricles, and joints, facilitating accurate diagnosis in diverse clinical scenarios.[5] Due to its essential role in these diagnostic imaging techniques, iohexol is included on the World Health Organization's Model List of Essential Medicines under radiocontrast media.[6]Administration and dosage
Iohexol is administered via multiple routes depending on the imaging procedure, including intravenous (IV) for computed tomography (CT) and angiography, intrathecal for myelography, oral for gastrointestinal (GI) tract visualization, rectal for lower GI studies, intra-articular for joint imaging, and direct injection into body cavities such as during endoscopic retrograde pancreatography (ERP) or hysterosalpingography.[7] The choice of route is guided by the specific diagnostic indication, with IV being the most common for systemic contrast enhancement in CT scans.[8] Dosage is determined by the iodine concentration of the formulation, ranging from 140 to 350 mgI/mL for injectable forms, and tailored to patient weight, age, and procedure type. For IV administration in adult CT head imaging, typical doses are 70-150 mL of 300 mgI/mL or 80 mL of 350 mgI/mL, administered as a bolus or infusion; for body CT, 50-200 mL of 300 mgI/mL is used.[9] In intrathecal myelography, adults receive 6-17 mL of 180-300 mgI/mL (total iodine 1.2-3.06 gI), injected slowly over 1-2 minutes, while pediatric doses are lower at 2-15 mL of 180 mgI/mL (total up to 2.7 gI), adjusted by age and weight.[8] For CT of the abdomen and pelvis, oral administration involves 500-1000 mL diluted to 6-12 mgI/mL, often combined with IV dosing; for radiographic examination of the GI tract, 50-100 mL of undiluted 350 mgI/mL may be used. Rectal doses for lower GI studies are similar in volume but delivered via enema.[7] Intra-articular injections for arthrography use 5-20 mL of 240-350 mgI/mL, and body cavity injections vary from 10-100 mL based on the site.[9] Maximum total iodine doses are limited, such as 250-290 mL (up to 87.5-101.5 gI) for IV/IA procedures and under 3.06 gI for intrathecal use to minimize risks.[8] Preparation involves using sterile technique for all injections, inspecting solutions for particulates or discoloration, and administering at body temperature (37°C) or room temperature (20-25°C); oral solutions may be diluted with water, juice, or milk just prior to use.[7] Single-use vials should be discarded after partial withdrawal to prevent contamination. Hydration protocols are essential, with patients encouraged to drink fluids before and after parenteral administration to reduce the risk of contrast-induced nephropathy.[9] Special considerations include dose reductions for pediatric patients (e.g., 1-3 mL/kg IV for CT) and those with renal impairment, where the minimum effective dose is used; for allergy-prone individuals, premedication may be employed, though routine test doses are not recommended—instead, emergency resuscitation equipment must be available.[8] Dosing intervals, such as 48 hours between intrathecal exams, help prevent cumulative toxicity.[7]| Route | Example Adult Dosage | Concentration (mgI/mL) | Notes |
|---|---|---|---|
| Intravenous (CT) | 70-150 mL bolus | 300 | Adjust for weight; max 150 mL |
| Intrathecal (Myelography) | 6-17 mL | 180-300 | Slow injection; max 3.06 gI |
| Oral (GI CT) | 500-1000 mL diluted | 6-12 | 20-60 min pre-IV; pediatric max 5 gI (<3 years) to 10 gI (3-18 years) |
| Intra-articular | 5-20 mL | 240-350 | For joint imaging only |