ACMT Toxicology Visual Pearl: Blue to the Rescue

3. Cesium

Background

The photo shows Prussian blue (ferric hexacyanoferrate II), which was originally developed as a pigment for painting and dyeing fabric in the early 18^th century [1]. It was later recognized for its ability to bind heavy metals, including cesium and thallium, as well as their radioactive isotopes [2].

What are Cesium and Thallium, and how are people exposed?

• Cesium is a naturally occurring element; in its pure form, it is a silvery white soft metal.
  • Found in low concentrations in rocks, soil, and dust [3].
  • Enters the water, soil, and air, and is taken up by plants [4].
  • Used in medical devices and for radiation brachytherapy [5].
  • Contamination from nuclear weapon testing, reactor accidents, and fuel reprocessing [3].
• Thallium is a naturally occurring element; in its pure form, it is a blueish-white soft metal.
  • Naturally occurs in earth’s crust and enters the air, water, and soil [6].
  • Industrial activities such as mineral smelting, coal-burning power plants, electronics manufacturing, optical lens production, and chemical catalyst production [6].
  • Historically found in rodenticides and in medical imaging techniques (cardiac scans) [6, 7].
  • Has a fascinating history and toxicology, which is beyond the scope of this discussion [8,9].

What is Prussian Blue’s Mechanism of Action for Cesium and Thallium Toxicity? [2,9,10]

• Prussian blue acts by binding cesium and thallium in the gastrointestinal tract through ion-exchange of the cesium and thallium cations with the potassium ions in its structure [8].
• This prevents reabsorption, decreases the half-life of cesium or thallium, and results in fecal excretion of the complex.
• Prussian blue is not systemically absorbed and remains in the gut lumen, where it can bind cesium and thallium during enterohepatic circulation.
• Prussian Blue is administered as oral capsules, under the brand name Radiogardase©.
  • Adult dosing: 1-3 grams PO every 8 hours
  • Children (2-12 years old): 1 gram PO every 8 hours
• Length of therapy is guided by monitoring cesium or thallium levels.
• Side effects include constipation and blue discoloration of stool.

Bedside Pearls

• Prussian blue is the primary treatment option for cesium and thallium toxicity.
• Prussian blue acts as an ion exchanger between cesium and/or thallium and potassium.