DESCRIPTION
Prussian blue insoluble capsules contain insoluble ferric hexacyanoferrate(II), with an empirical formula of Fe4 [Fe(CN)6 ]3 and a molecular weight of 859.3 Daltons. It is provided as 0.5 gram of Prussian blue powder in gelatin capsules with 0-38 mg of microcrystalline cellulose. The dark blue capsules are imprinted with the light blue inscription: PB. The powder may vary from uniformly fine, dark granules to coarse light and dark-colored granules. The structural formula for Prussian blue insoluble is shown below.
(click image for full-size original) The crystal structure of Prussian blue is a cubic lattice with the Fe(II) and Fe(III) atom occupying the corners of the cube and the cyanide groups positioned on the sides.
CLINICAL PHARMACOLOGYGeneral
Prussian blue insoluble, ferric(III) hexacyanoferrate(II), after oral ingestion is not absorbed through the intact gastrointestinal wall. Its clearance from the body depends on the gastrointestinal tract transit time. Prussian blue insoluble acts by ion-exchange, adsorption, and mechanical trapping within the crystal structure and has a very high affinity for radioactive and non-radioactive cesium and thallium.
Prussian blue insoluble binds cesium and thallium isotopes in the gastrointestinal tract after these isotopes are ingested or excreted in the bile by the liver thereby reducing gastrointestinal reabsorption (enterohepatic circulation). In studies of rats, pigs, and dogs that were internally contaminated with cesium and thallium, the presence of the insoluble complexes in the gastrointestinal lumen, changed the primary elimination route from the kidney to the feces and increased the rate of elimination of these two contaminants.
The rate of cesium and thallium elimination was proportional to the duration and dose of Prussian blue insoluble. (See CLINICAL PHARMACOLOGY, Pharmacokinetics.) A radioactive element has a constant rate of disintegration that is reflected by its physical half-life. The rate of element elimination from the body is reflected by its biologic half-life. The combined rate of radiation disintegration and rate of element elimination is reflected by the effective half-life.
Cesium-137 (137 Cs) has a physical half-life of 30 years with a beta energy peak at 174.0 keV. Following entry into the blood, it is distributed uniformly through all body tissues. Approximately 10% of cesium is eliminated rapidly with a biological half-life of 2 days, and 90% is eliminated more slowly, with a biological half-life of 110 days. Less than 1% of the cesium was retained with a longer biological half-life of about 500 days. Cesium follows the movement of potassium and is excreted into the intestine, reabsorbed from the gut into the blood, then to the bile, where it is excreted again into the gut (enterohepatic circulation). Without Prussian blue insoluble treatment, ~80% of cesium is excreted through the kidneys and ~20% in the feces. Because of cesium’s long physical half-life, the rate of radiation elimination is similar to the rate of element elimination from the body.
Thallium-201 (201 Tl) has a physical half-life of 3 days with electron and photon emissions with a gamma energy peak at 167.4 keV. Following entry into the blood, thallium is distributed in the kidneys (3%) and all other organs (97%). Non-radioactive thallium, depending upon the tissue, has a biological half-life of 8 – 10 days. Thallium also follows the movement of potassium and is excreted by the bile