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Iohexol

  • Diagnostic agentsDiagnostic agents

A non-ionic iodinated contrast medium for CT, angiography and other X-ray studies. Leaves unchanged through the kidneys.

Updated

Quick facts

Group
Diagnostic agents
Target
No pharmacological target: its iodine atoms block X-rays
Used for
Contrast CT of the head and body
Key effects
Warmth or pain during injection · Nausea and vomiting
Monitor
Kidney function before the study · Thyroid function
ATC
V08AB02

No doses: the clinician sets them by the current guideline.

Mechanism of action

Iohexol carries iodine atoms that absorb X-rays more than soft tissue does. Wherever it goes (blood vessels, kidney, spinal canal, joints, bowel), that space shows up white on the image. It is non-ionic, so it is better tolerated than older ionic agents, but it is still hypertonic to blood and cerebrospinal fluid.

  1. Iohexol fills the vessel, organ or space being studied
  2. Its iodine atoms absorb X-rays
  3. That space appears white on CT or radiography
  4. The kidneys excrete it unchanged

Indications

  • Contrast CT of the head and body, angiography, venography and urography
  • Myelography and CT cisternography (only the presentations approved for intrathecal use)
  • Oral or rectal studies of the gut, arthrography and body cavity studies

Adverse effects

Common

  • Warmth or pain during injection
  • Nausea and vomiting
  • After intrathecal use: headache, back and neck pain, dizziness
  • After oral use: diarrhoea and abdominal pain

Contraindications

  • Intrathecal use of any presentation not approved for that route
  • Hysterosalpingography in pregnancy, during menstruation, with genital infection or soon after a uterine procedure

Key interactions

Metformin
Contrast-induced kidney injury can lead to lactic acidosis; metformin is usually paused around the study in people at risk
Radioactive iodine tests and treatment
Thyroid iodine uptake is reduced for weeks, so these are postponed

What is monitored

  • Kidney function before the study in people at risk
  • Signs of an allergic reaction during and after injection
  • Thyroid function in children under 3 years after exposure

Administration and safety

  • The label, route and presentation are checked before every intrathecal use: only presentations approved for that route are used.
  • Good hydration before and after the study lowers the risk of kidney injury.
  • The IV site is watched for extravasation, which can injure tissue.
  • Emergency treatment for anaphylaxis is ready in the room.

Pregnancy and breastfeeding

Animal studies showed no birth defects and human data are limited; breastfeeding does not need to stop after an injection.

Nursing care

  • Ask about earlier contrast reactions, asthma, kidney disease, diabetes, hyperthyroidism and metformin use.
  • Check that kidney function results are available when required.
  • Observe the patient after the injection and teach them to report a late rash or breathing trouble.
  • Encourage fluids after the study unless restricted.

Pharmacokinetics

Absorption
Very little is absorbed when given by mouth
Distribution
After IV injection it spreads through the extracellular fluid
Metabolism
Not metabolised
Elimination
Excreted unchanged by the kidneys, mostly within a day; removed by dialysis

Test yourself

Think of the answer, then tap the question to see it.

Why does iohexol show up white on CT?

Its iodine atoms absorb X-rays more than soft tissue.

Why is metformin often paused around an iodinated contrast study?

If contrast injures the kidneys, metformin can accumulate and cause lactic acidosis.

What is the most dangerous route error with iohexol?

Giving a presentation not approved for intrathecal use into the spinal canal: seizures, brain oedema, paralysis or death.

Which thyroid problems can iodinated contrast cause?

Thyroid storm in hyperthyroidism and thyroid dysfunction in children under 3 years.

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Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: DailyMed - IOHEXOL injection, solution (DailyMed (U.S. National Library of Medicine), 2026); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).

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