Potassium chloride treatment in thallotoxicosis

Central nervous system effects in acute thallium poisoning

We report the central nervous system manifestations, neuropsychological studies and brain magnetic resonance image (MRI) findings of two patients with acute thallium intoxication. Neurologically the patients suffered from confusion, disorientation, and hallucination in the acute stage, followed by anxiety, depression, lack of attention, and memory impairment, in addition to peripheral neuropathy. Neuropsychological tests revealed an impairment of memory function, including reversed digital span, memory registration, memory recall, memory recognition, similarity, proverb reasoning, and verbal fluency. High concentrations of thallium were found in the urine, blood, and drinking water of these two patients. Brain MRI showed lesions in the corpus striatum in one patient. During the follow-up periods, the clinical manifestations and neuropsychological studies showed a slowly progressive improvement, and a follow-up brain MRI 1.5 months later demonstrated a resolution of the lesions. We conclude that thallium intoxication might induce encephalopathy, and brain MRI studies demonstrated the acute-stage brain lesions in a severe intoxicated patient. In addition, neuropsychological tests also confirmed memory deficits, although the brain lesions in the corpus striatum might resolve.

Thallium toxicity and the role of Prussian blue in therapy

Thallium salts have been used as medicinal agents, as key ingredients in a variety of manufacturing processes, and as a potent rodenticide. Additionally, environmental concerns are growing, as thallium is a waste product of coal combustion and the manufacturing of cement. Thallium salts are rapidly and nearly completely absorbed by virtually all routes, with gastrointestinal exposure being the most common route to produce toxicity. Thallium enters cells by a unique process governed by its similarity in charge and ionic radius to potassium. Although the exact mechanism of toxicity has not been established, thallium interferes with energy production at essential steps in glycolysis, the Krebs cycle, and oxidative phosphorylation. Additional effects include inhibition of sodium-potassium-adenosine triphosphatase and binding to sulfhydryl groups. The major manifestations of toxicity consist of a rapidly progressive, ascending, extremely painful sensory neuropathy and alopecia. Unlike exposure to most metal salts, gastrointestinal symptoms of thallium toxicity are relatively minor, and constipation is more characteristic than diarrhoea. Many other findings such as an autonomic neuropathy, cranial nerve abnormalities, altered mental status, motor weakness, cardiac, hepatic, and renal effects are described, but are less specific. Thallium also crosses the placenta freely and produces abnormalities in animals as well as fetal demise, overt toxicity and congenital abnormalities in humans. There are no controlled trials of treatments in thallium-poisoned patients. Thus, the literature is predominated by very small animal studies and case reports with very limited data. Strong evidence speaks against the use of traditional metal chelators such as dimercaprol (British Anti-Lewisite) and penicillamine, and the latter may cause redistribution of thallium into the central nervous system. Likewise, forced potassium diuresis appears harmful. The use of single- or multiple-dose activated charcoal is supported by in vitro binding experiments and some animal data, and charcoal haemoperfusion may be a useful adjunct. Multiple animal studies give evidence for enhanced elimination and improved survival with Prussian blue. Unfortunately, despite the fact that many humans have been treated with Prussian blue, the data presented are insufficient to comment definitively on its efficacy. However, Prussian blue's safety profile is superior to that of other proposed therapies and it should be considered the drug of choice in acute thallium poisoning. Public health efforts should focus on greater restrictions on access to, and use of, thallium salts.

Comparative efficacy of thallium adsorption by activated charcoal, prussian blue, and sodium polystyrene sulfonate

BACKGROUND

Although Prussian blue is considered the antidote of choice for thallium poisoning, the lack of a Food and Drug Administration-approved pharmaceutical formulation has led to the search for other adsorbents. Activated charcoal has been demonstrated to adsorb thallium in vitro, and the similarity between thallium and potassium has led some authors to consider the use of sodium polystyrene sulfonate as a potential adsorbent. This experiment was designed to compare the relative thallium binding efficacy of these agents in a standard isotherm model.

METHODS

A standard aqueous solution of thallium acetate buffered to pH 7.0 was agitated at 25 degrees C with activated charcoal, Prussian blue, or sodium polystyrene sulfonate at adsorbent:thallium ratios ranging from 1.5:1 to 100:1. In order to further simulate physiologic conditions, all trials were repeated in a solution containing 4 mmol/L potassium phosphate. After thorough agitation, the mixtures were allowed to settle and were centrifuged and filtered through a 0.22-micron filter. Supernatant thallium concentrations were measured by atomic absorption spectrophotometry. Langmuir isotherms were used to calculate the maximal adsorptive capacity of each adsorbent, using linear regression with Pearson's correlation coefficients (r). Maximal adsorptive capacities were compared statistically with a p < 0.05 considered significant.

RESULTS

The maximal adsorptive capacities defined as milligrams of thallium per gram of adsorbent (shown with linear regression p and r values) were as follows: activated charcoal, 59.7 mg/g (p = 0.005, r = 0.995); Prussian blue, 72.7 mg/g (p = 0.004, r = 0.996); and sodium polystyrene sulfonate, 713 mg/g (p = 0.049, r = 0.951). All three values were statistically different from each other. At a physiologic potassium concentration, the maximal adsorptive capacities for activated charcoal and Prussian blue were essentially unchanged (58.3 mg/g and 69.8 mg/g, respectively, p > 0.05 for each vs trials without potassium), while the maximal adsorptive capacity for sodium polystyrene sulfonate fell to 39.1 mg/g (p = 0.003, r = 0.997, p = 0.005 vs sodium polystyrene sulfonate without potassium).

CONCLUSIONS

This in vitro study confirms the utility of Prussian blue and activated charcoal as thallium adsorbents. Although sodium polystyrene sulfonate demonstrates exceptional in vitro adsorption of thallium, its greater affinity for potassium probably renders it clinically ineffective.

Thallium poisoning. Diagnosis may be elusive but alopecia is the clue

Thallium is a heavy metal whose salts are used in some rodent poisons and in the manufacture of optical lenses, semiconductors, scintillation counters, low temperature thermometers, and switching devices, green coloured fireworks, and imitation jewelery, and as chemical catalysts. In clinical practice thallium isotopes are used in cardiac scanning, but the use of thallium salts to treat scalp ringworm was abandoned earlier this century because of their toxicity. The sale of thallium in Britain is strictly licensed because of its toxicity and potential for use in murder, which is helped by the fact that thallous salts are colourless, tasteless, and odorless. The more water soluble salts (such as thallium sulphate, acetate, or carbonate) have higher toxicity, and although the toxic dose is variable most deaths occur after the ingestion of 10-15 mg/kg of soluble salt. Most cases of thallium toxicity occur after oral ingestion but severe toxicity has been reported after inhalation of contaminated dust from pyrite burners, in zinc and lead smelting, and in the manufacture of cadmium, after dermal absorption through protective rubber gloves, and after snorting what was thought to be cocaine. The elimination half time of thallium is between 1.7 and 30 days depending on the time since, and chronicity of, ingestion. The elimination time phases are apparent and because of the long terminal elimination half time thallium may act as a cumulative poison. We present two cases of thallium poisoning with intent to kill.

Current status of antidotal therapies in acute human intoxications

The purpose of this work is a review of usefulness, indications and handling of some antidotes which are at our disposal for therapeutic use since several years, especially naloxone, flumazenil, Fab fragments of digoxin specific antibodies, hydroxocobalamine, 4-methyl-pyrazole, N-acetylcystein or the new metal chelators. Older clinically relevant substances are also reviewed.

Cardiopulmonary effects of acute thallium poisoning

Gastrointestinal distress and alopecia are the most commonly reported symptoms of acute thallium intoxication; however, cardiac and pulmonary disease may dominate the acute stages of the disease. We report four cases which illustrate the importance of cardiac and respiratory disease in this syndrome.

Acute thallium poisoning: an evaluation of different forms of treatment

Hemodialysis, forced potassium diuresis, chelating agents per os, and Dithiocarb given intravenously during short periods of time were used for the treatment of acute thallium poisoning (ingestion of 750 mg of thallium sulfate), and the effectiveness of these different therapeutic procedures was analyzed. Chelating agents per os (Prussian blue, Dithiocarb, and Dithiozone) were ineffective in our patient, since fecal excretion of thallium was very low and unmodified by them. Forced potassium diuresis and hemodialysis were very useful therapeutic measures, especially in the first 12 days following ingestion. Dithiocarb perfusion seems to be the most effective method for enhancing urinary thallium excretion. This method might be most useful in the treatment of thallium poisoning if its deleterious effects could be eliminated.