Prussian Blue for Treatment of Radiocesium Poisoning

Dennis F. Thompson, Pharm.D., FASHP, FCCP, and Chelsea O. Church, Pharm.D.

Disclosures

Pharmacotherapy. 2001;21(11) 

In This Article

Prussian Blue Therapeutics

Prussian blue, a crystal lattice of potassium ferrihexacyanoferrate (II), usually is given orally and is not significantly absorbed. Prussian blue adsorbs that fraction of cesium secreted into the gut, binds it in the lumen, and exchanges potassium for cesium on the surface of the crystal lattice. However, as with other drugs that dialyze the intestine,[11,12,13] Prussian blue probably traps the cesium that is secreted into the intestinal lumen and would otherwise be reabsorbed into the systemic circulation. In one study,[14] patients poisoned with radiocesium had a physiologic urine-to-feces excretion ratio of 4:1 that was reversed to 1:4 under the influence of Prussian blue. The effect of Prussian blue is independent of cesium half-life. Prussian blue can reduce cesium half-life by approximately the same percentage, whether the individual has a long or short cesium half-life.[15]

Prussian blue can be administered in two different physicochemical forms. Both soluble (colloidal) and insoluble (noncolloidal) Prussian blue can be administered to treat radiocesium poisoning. Binding characteristics of these forms were studied both in vitro and in vivo. Insoluble Prussian blue appears to be slightly more effective in vitro,[16] whereas soluble and insoluble Prussian blue are about equally effective in vivo.[17] Differences in quality of preparation, particle size, and local pH level can each affect cesium adsorption to the Prussian blue crystal lattice.[18,19] These physicochemical factors may explain some of the variability in its efficacy seen among patients.

Prussian blue is relatively nontoxic when given orally.[20,21] Because potassium is exchanged for cesium at the surface of the crystal lattice, potassium levels should be monitored. Mild cases of hypokalemia have been described, with potassium levels returning to normal after potassium replacement was begun.[14] However, constipation in patients given Prussian blue for thallium poisoning can be disastrous. In a series of 11 cases of thallium poisoning,[22] persistently high blood levels of thallium were found despite Prussian blue therapy in patients who were becoming constipated. The authors speculated that thallium may have been liberated from the Prussian blue complex and reabsorbed over time. Consequences of this occurring with radiocesium could be equally tragic, with additional, prolonged exposure of radioactive cesium to the intestinal lumen.[22,23] Administering 15% mannitol with Prussian blue has been recommended to maintain adequate fecal movement.[23] The study mentioned above[14] found a 20% frequency of constipation in 46 patients who received Prussian blue for radiocesium poisoning related to the Goiania tragedy. The authors recommended prophylactic administration of light laxatives to decrease the amount of time the contaminated feces were in contact with the intestinal lumen.

Prussian blue is not commercially available in the United States. It is often available in pathology and clinical laboratories since it is used in certain staining procedures. Prussian blue is available internationally under the trade names Radiogardase-Cs and Antidotum Thallii-Heyl (Heyl; Berlin, Germany).

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