Thallium is a soft metal that quickly oxidizes upon exposure to air. It is a minor constituent in a variety of ores. Thallium salts are used in the manufacture of jewelry, semiconductors, and optic devices. It is no longer used in the United States as a depilatory or rodenticide because of its serious human toxicity. Thallium exposure has been reported after ingestion of contaminated herbal preparations and adulteration of illicit drugs.

The exact mechanism of thallium toxicity is not known. It appears to affect a variety of enzyme systems, resulting in generalized cellular poisoning. Thallium metabolism is similar to that of potassium, and it may inhibit potassium flux across biologic membranes by binding to Na⁺/K⁺-ATP transport enzymes. It may also impair glutathione metabolism and increase cellular oxidative stress.

The minimum lethal dose of thallium salts varies depending on the compound. The more water-soluble salts (eg, thallous acetate and thallic chloride) are slightly more toxic than the less soluble forms (thallic oxide and thallous iodide). Some thallium salts are well absorbed across intact skin.

Symptoms do not occur immediately but are typically delayed for hours to days following exposure.

1. Acute effects include abdominal pain, nausea, vomiting, and diarrhea (sometimes with hemorrhage). Shock may result from massive fluid or blood loss. Within 2-3 days, delirium, seizures, respiratory failure and death may occur.
2. Chronic effects include painful peripheral neuropathy, myopathy, chorea, stomatitis, ophthalmoplegia, hair loss and nail dystrophy (Mees' lines).

Thallotoxicosis should be considered when gastroenteritis and painful lower extremity paresthesias are followed by alopecia.

1. Specific levels. A 24-hour urinary thallium concentration is the standard diagnostic test for thallium exposure (normal typically <5 mcg/L). Spot urine thallium concentrations are unreliable. Normal whole blood thallium concentrations are <2 mcg/L. Hair levels are of limited value, used mainly in documenting past exposure and in forensic cases.
2. Other useful diagnostics studies include CBC, electrolytes, glucose, BUN, creatinine, CK, hepatic aminotransferases, cardiac troponin, and ECG. Because thallium is radiopaque, abdominal radiographs may be useful after an acute ingestion.

1. Emergency and supportive measures
   1. Maintain an open airway and assist ventilation if necessary.
   2. Cardiac monitoring for any patient with abnormal ECG or unstable vital signs.
   3. Treat seizures and coma if they occur.
   4. Treat gastroenteritis with IV replacement of fluids (and blood if needed). Use vasopressors if shock does not respond to fluid therapy.
2. Specific drugs and antidotes. There is currently no recommended specific treatment in the United States.
   1. Prussian blue (ferric ferrocyanide) is the mainstay of therapy. This compound has a crystal lattice structure that binds thallium ions and interferes with enterohepatic recirculation. Insoluble Prussian blue (Radiogardase) is available as 500-mg tablets, and the recommended adult dose is 3 g orally 3 times per day (1 g orally 3 times per day for children ages 2-12). In the United States, Prussian blue should be available through pharmaceutical suppliers. It is also available through CDC emergency supply hotline at 770-488-7100 as a part of the US National Strategic Stockpile. Emergency supply may also be available through Oak Ridge Associated Universities at 1-865-576-1005 and the Radiation Emergency Assistance Center/Training Site (REAC/TS) 24-hour phone line.
   2. Chelation therapy has been tried without demonstrated benefit. Penicillamine and diethyldithiocarbamate should be avoided because studies have suggested that they contribute to redistribution of thallium to the brain.
3. Decontamination . Administer activated charcoal orally if conditions are appropriate (see Table I-37,). Consider gastric lavage for large recent ingestions. Whole bowel irrigation may be helpful for patients with presence of radiopaque material in gastrointestinal tract.
4. Enhanced elimination.
   1. Multidose activated charcoal enhances fecal elimination by binding thallium secreted into the gut lumen or via the biliary system, interrupting enterohepatic or enteroenteric recirculation. For patients with constipation, consider addition of cathartic if otherwise safe (preferably mannitol) until Prussian blue is available.
   2. Extracorporeal drug removal with hemodialysis may be beneficial in patients with large overdose, renal dysfunction, life-threatening clinical manifestations, or thallium concentration of >400 mcg/L (if concentrations are readily available). Continuous renal replacement therapy is an alternative if hemodialysis is not available.