Thallium intoxication treated with combined hemoperfusion-hemodialysis

Thallium toxicosis in a dog consequent to ingestion of Mycoplasma agar plates

A 1-year-old dog ingested a mixture of blood agar and Mycoplasma agar plates. The Mycoplasma agar plates contained thallium acetate, which resulted in an estimated minimum dose of 5 mg thallium acetate/kg bodyweight. Clinical signs over the course of 2-3 weeks included vomiting, diarrhea, weight loss, alopecia, dysphonia, ataxia, paresthesia, intension tremors, megaesophagus with subsequent aspiration pneumonia, and several seizure episodes. The dog was treated with intravenous fluids and placement of a gastric feeding tube. Thallium concentrations in hair were 8.2 µg/g in samples taken on day 19, 16.4 µg/g in samples taken 3 months after exposure, 13.4 µg/g in samples taken 5 months after exposure, and nondetectable in samples taken 7 months after exposure. The blood thallium concentration was 190 µg/l on day 19 and nondetec table 3 months after exposure. Megaesophagus and dysphonia continued for 10 months after exposure. This case of thallium poisoning following ingestion of mycoplasma agar plates demonstrates that unusual sources of thallium still exist and suggests that thallium toxicosis should be included in the list of differential diagnoses in dogs presented with megaesophagus, especially if alopecia and other unexplained peripheral neuropathies are present. Hair and blood samples are useful specimens to reach an accurate diagnosis even if taken several weeks post exposure. The postexposure blood and hair thallium concentrations reported in this case are useful data for diagnosticians investigating dogs with potential thallium poisoning.

Heavy metal poisoning: management of intoxication and antidotes

Of the known elements, nearly 80% are either metals or metalloids. The highly reactive nature of most metals result in their forming complexes with other compounds such oxygen, sulfide and chloride. Although this reactivity is the primary means by which they are toxic, many metals, in trace amounts, are vital to normal physiological processes; examples include iron in oxygen transport, manganese and selenium in antioxidant defense and zinc in metabolism. With these essential metals toxicity occurs when concentrations are either too low or too high. For some metals there are no physiological concentrations that are beneficial; as such these metals only have the potential to cause toxicity. This chapter focuses on four of these: arsenic, mercury, lead and thallium.

Soluble or Insoluble Prussian Blue for Radiocesium and Thallium Poisoning?

OBJECTIVE:

To review the available English-language literature concerning the efficacy of soluble and insoluble Prussian blue used as a therapeutic agent in radiocesium and thallium poisoning.

DATA SOURCES:

A thorough search of MEDLINE, Toxline, and EMBASE databases (1960s-August 2003) was performed. Search terms included Prussian blue, thallium, and radiocesium poisoning. Bibliographies of relevant papers were reviewed for additional citations.

STUDY SELECTION AND DATA EXTRACTION:

Reports and studies of human trials and cases, along with animal and relevant in vitro data, were sought. Data were categorized as insoluble and soluble Prussian blue and by thallium and radiocesium poisoning.

DATA SYNTHESIS:

The majority of evidence describing the efficacy of Prussian blue for radiocesium poisoning is based on the use of the insoluble form. In contrast, the majority of data supporting the efficacy of Prussian blue in thallium poisoning involves the use of the soluble form.

CONCLUSIONS:

Insoluble Prussian blue has recently been approved in the US for treatment of both thallium and radiocesium poisoning. While there is sufficient evidence that the insoluble form of Prussian blue is effective in radiocesium poisoning, there is a paucity of analogous data supporting its use in thallium poisoning. Whether the physicochemical differences between soluble and insoluble Prussian blue have any effect on outcomes in human poisoning is not known.

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.

Treatment of severe thallium intoxication

CASE REPORT

We report a successfully treated case of severe thallium intoxication. In spite of very high serum thallium (5,240 micrograms/L), symptomatology was minor and recovery complete. Prussian Blue was administered, diuresis was enhanced by intravenous fluids and a prolonged hemodialysis was started early. High blood flows (300 mL/min) and intravenous potassium chloride supplements, to mobilize thallium from the tissues, resulted in good clearances (96 to 150 mL/min). In order to prevent the well known complications, we recommend aggressive treatment of severe thallium intoxication.

Near fatal subacute thallium poisoning necessitating prolonged mechanical ventilation

The authors describe a case of severe sensory-motor polyneuropathy caused by subacute thallium-intoxication rapidly progressing to respiratory failure due to complete muscle paralysis. After more than 2 months of mechanical ventilation, weaning from the ventilator was possible. Further intensive physical rehabilitation required an additional 6 months hospital stay, and 18 months later, neurological recovery was complete except for the distal lower limbs muscles. The authors discuss the different forms of thallotoxicosis and the present treatment is reviewed. Maximal prolonged therapeutic support should be offered in severe thallotoxicosis because of possible near complete recovery.

Combined hemoperfusion-hemodialysis in severe poisoning: kinetics of drug extraction

We studied the kinetics of drug extraction during a combined hemoperfusion-hemodialysis procedure for treatment of severely poisoned patients. In most drugs studied an overall clearance of 120-180 ml/min (at a blood flow of 200 ml/min) was obtained, the relative contribution of hemoperfusion and hemodialysis being variable. A one-compartment pharmacokinetic model is presented that allows calculation of the optimal treatment time as a function of the extracorporeal clearance and the distribution volume of the toxic agent. For some drugs two-compartment kinetics were observed during treatment. The behaviour during treatment of these drugs is illustrated with computer simulation.

Thallium poisoning--toxin elimination and therapy in three cases

Three cases of thallium poisoning occurred within the same family after eating a meal of poisoned sour milk. The 58 year old mother died after four days cardiovascular insufficiency. Massive thallium concentrations were found in blood, urine, liver and kidney. The 59 year old father presented after four days with a neurology typical for classic thallotoxicosis with potentially lethal blood thallium levels. This patient recovered after therapy including Prussian Blue, forced diuresis and two six hour hemoperfusions with a charcoal column. Urinary elimination of thallium over two weeks was almost 300 mg, whereas a maximum total of 63 mg were removed with hemoperfusion. A retrospective estimate of the total dose ingested and the large distribution volume of thallium suggest that hemoperfusion did not affect the course of the intoxication. The 28 year old son, later convicted for homicide, was admitted on the tenth day after the meal with very discrete neurological symptoms. This patient had low blood and urine thallium levels. He recovered uneventfully after treatment with Prussian Blue and forced diuresis. However, both surviving patients developed alopecia after two weeks. All three patients had raised liver transaminases. Intensive therapy with gut decontamination, Prussian Blue and forced diuresis should be the mainstay of therapy.