Prussian blue
Specific antidotes
Specific antidotes
Oral capsules that trap radioactive caesium and thallium in the gut so they leave in the stool. Stools may turn blue.
Also called: ferric hexacyanoferrate, potassium ferric hexacyanoferrate
Quick facts
- Group
- Specific antidotes
- Target
- Caesium and thallium ions in the intestine
- Used for
- Poisoning with radioactive
- Key effects
- Constipation · Upset stomach · Blue stools
- Monitor
- Radioactivity · Bowel habit
- ATC
- V03AB31
No doses: the clinician sets them by the current guideline.
Mechanism of action
Caesium and thallium that have been absorbed are secreted by the liver into bile and then reabsorbed from the gut (enterohepatic circulation). Prussian blue stays in the intestine and works as an ion exchanger: it traps these ions so they leave in the stool instead of being reabsorbed. This shortens their stay in the body, so the radiation dose or toxic exposure falls.
- Absorbed caesium or thallium cycles from bile back to the gut
- Prussian blue traps the ions in the intestine
- They leave in the stool instead of being reabsorbed
- Their time in the body is shortened
Indications
- Known or suspected internal contamination with radioactive caesium
- Poisoning with radioactive or non-radioactive thallium
Adverse effects
- Constipation
- Upset stomach
- Blue stools; blue mouth or teeth if the capsule is opened and mixed with food
Contraindications
- Caution in bowel obstruction or severe constipation, which slow its action
- Infants under two years: safety not established
- Artist's Prussian blue pigment is never a substitute and can be harmful
Key interactions
- Potassium iodide and calcium or zinc DTPA
- May be given together when the radioactive contaminant is unknown; each binds different elements
What is monitored
- Radioactivity or thallium levels to decide how long treatment continues
- Bowel habit, to detect constipation early
Administration and safety
- Prescription only, given under medical or public-health direction
- Capsules can be opened and mixed with food or drink for people who cannot swallow them
- Started as soon as possible after exposure, but still useful when started later
Pregnancy and breastfeeding
CDC considers it safe for most adults, including pregnant women; it is not absorbed from the gut.
Nursing care
- Warn that stools will turn blue
- Ask about constipation and treat it, since slow transit reduces the drug's effect
- Collect urine or stool samples as instructed for dose monitoring
- Warn against artist's pigment, which is not a medicine
Pharmacokinetics
- Absorption
- Not meaningfully absorbed; acts inside the gut
- Elimination
- Excreted in the faeces together with the trapped ions
Test yourself
Think of the answer, then tap the question to see it.
Which two elements does Prussian blue remove?
Caesium (radioactive) and thallium (radioactive or not).
How does Prussian blue speed up their removal?
It traps them in the gut and breaks their enterohepatic circulation, so they leave in the stool.
What are the most common side effects of Prussian blue?
Constipation and upset stomach; stools also turn blue.
Connections
← Back to the class: Specific antidotes
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: Treating Radiation Exposure with Prussian Blue | Radiation Emergencies | CDC (U.S. Centers for Disease Control and Prevention, 2026); Questions and Answers on Prussian Blue (U.S. Food and Drug Administration (archived), 2011); eEML - Electronic Essential Medicines List (World Health Organization, 2025); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).
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Representative model, for educational purposes only.