[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [Diagnostic agents](https://durgical.com/en/pharmacology/classes/diagnostic-agents/) › Iohexol

# Iohexol

## Diagnostic agents?

Diagnostic agents

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

Updated Nov 1, 2026

## Quick facts

**Group**
[Diagnostic agents](https://durgical.com/en/pharmacology/classes/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.

On this page

- The basics Mechanism of action
- Indications
- Adverse effects
- Pharmacokinetics
- Memory aid

- Safety Contraindications
- Key interactions
- What is monitored
- Administration and safety
- Pregnancy and breastfeeding
- Nursing care

- Study Test yourself

- Connections Connections

## 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.

- Iohexol fills the vessel, organ or space being studied
- Its iodine atoms absorb X-rays
- That space appears white on CT or radiography
- 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

### Serious (rare, important)

- Hypersensitivity reactions, including anaphylaxis
- Contrast-associated acute kidney injury, mainly with kidney disease, dehydration or diabetes
- Shock, cardiac arrest and thromboembolic events
- Thyroid storm in hyperthyroidism; thyroid dysfunction in children under 3 years
- Hypertensive crisis in phaeochromocytoma; sickle cell crisis; severe skin reactions; seizures and death if the wrong product is given intrathecally

## 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

## Memory aid

IOhexol = IOdine for X-rays: not metabolised, out by the kidney; so think «kidneys, metformin and thyroid».

## 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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## Connections

## Related drugs 2

- [Metformin](https://durgical.com/en/pharmacology/metformin/)
- [Fluorescein](https://durgical.com/en/pharmacology/fluorescein/)

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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](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=ff9456ef-c45a-450d-9004-a684af2bcc59) (DailyMed (U.S. National Library of Medicine), 2026); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=V08AB02) (WHO Collaborating Centre for Drug Statistics Methodology, 2026).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/pharmacology/iohexol/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/iohexol/