An antidote that binds radioactive caesium or thallium in the gut
Prussian blue
An oral antidote that binds radioactive caesium or thallium in the gut so the body can remove them more quickly.
What is Prussian blue?
Prussian blue is a specialist antidote taken by mouth to treat poisoning with radioactive caesium or with thallium. It works in the gut, where it traps these substances so they are passed out in the stools instead of being reabsorbed, speeding their removal from the body. A harmless but striking effect is that it turns the stools blue. It can lower blood potassium and commonly causes constipation, so these are watched for. It is a specialist treatment used under expert and, for radioactive exposure, public-health guidance.
Education and reference only. This is a plain-language guide to Prussian blue — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Prussian blue is a medicine used as an antidote in poisoning with radioactive caesium (for example after a radiation incident) or with thallium (a heavy metal used in some poisons). Taken by mouth as capsules, it works inside the gut rather than being absorbed into the body. By binding these harmful substances so they leave in the stools, it shortens the time they stay in the body and the amount of radiation or poison the person is exposed to. It is a specialist antidote, used under expert guidance and, in the case of radioactive caesium, as part of a coordinated public-health response.
How it works
Caesium and thallium that get into the body are partly recycled: they pass into the gut and are then reabsorbed back into the bloodstream, which keeps them circulating. Prussian blue acts like a sponge in the gut, binding these substances so they can no longer be reabsorbed and are instead carried out in the stools. This interrupts the recycling loop, so each pass through the gut removes more of the poison, speeding the fall in body levels. Because it stays in the gut and is not absorbed itself, it works locally; it is taken regularly over a period so it keeps trapping the substance as it cycles through.
Company & origin
Originated / developed by: Specialist manufacturer.
A specialist antidote used in the UK to speed the removal of radioactive caesium or thallium from the body after poisoning, taken by mouth.
Practical use
How to take Prussian blue
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Take the capsules by mouth as directed, regularly and for the full course you are given.
- Do not be alarmed that your stools turn blue; this is a harmless effect of the medicine.
- Drink plenty of fluids and tell your team if you become constipated, as this is common.
- Attend the blood tests you are asked to have, as it can lower potassium.
- Follow the specialist and public-health advice given, particularly after radioactive exposure.
Weighing it up
Advantages & disadvantages of Prussian blue
Advantages
- Speeds the removal of radioactive caesium or thallium, reducing how long they stay in the body.
- Taken simply by mouth and works in the gut without being absorbed.
- A specific antidote for poisonings that are otherwise very difficult to treat.
Disadvantages
- Commonly causes constipation, which can slow how well it works.
- Can lower blood potassium, so monitoring is needed.
- Turns the stools blue, and is a specialist treatment needing expert guidance.
Practical use
Good to know
The main thing to understand about prussian blue is that it works inside the gut, trapping radioactive caesium or thallium so they leave the body in the stools rather than being reabsorbed; it is not absorbed into the body itself. A harmless but noticeable effect is that it turns the stools blue. Two practical points are that it commonly causes constipation, which can slow its own effect by keeping things in the gut longer, so a healthy fluid intake and sometimes treatment for constipation are encouraged; and that it can lower blood potassium, so this is checked, especially with longer courses. It is a specialist antidote, usually given under expert toxicology advice and, for radioactive exposure, alongside a wider public-health response, and it is taken regularly for as long as advised.
Who should not take it / use with caution
- People who have had a serious allergic reaction to it should not take it.
- It is used with care in people with constipation or bowel problems, which it can worsen.
- It is used with care in people prone to low potassium, with monitoring.
Monitoring
- Blood tests to check potassium, especially during longer courses.
- Watching for and managing constipation.
- Reviewing how body levels of caesium or thallium are falling, where this can be measured.
Side effects
- Constipation, which is common and may need treating.
- Blue colouring of the stools, which is harmless.
- A fall in blood potassium, especially with longer courses, which is why it is monitored.
Key interactions
- Because it binds substances in the gut, it may reduce the absorption of some other medicines taken at the same time.
- Spacing other oral medicines apart from it may be advised, on specialist guidance.
- Tell your team about all your medicines so timing can be managed.
Available as: Capsules taken by mouth.
Answers
Prussian blue: frequently asked questions
What is prussian blue used for?
It is a specialist antidote taken by mouth to treat poisoning with radioactive caesium or with thallium, speeding their removal from the body.
How does it work?
It acts like a sponge in the gut, binding caesium or thallium so they leave in the stools instead of being reabsorbed, which interrupts their recycling and lowers body levels faster.
Why are my stools blue?
Turning the stools blue is a harmless and expected effect of prussian blue and is nothing to worry about.
What side effects should I watch for?
Constipation is common, and the medicine can lower blood potassium, so drinking plenty of fluids, treating constipation and having blood tests are all part of treatment.
Is it given on its own?
It is a specialist antidote used under expert toxicology advice and, after radioactive exposure, alongside a wider public-health response, and it is taken regularly for as long as advised.
Authoritative sources
- BNF
- NICE CKS
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